For those who are skeptical about propellers - Team 2526
 

The props both spin at about 7000 rpm, but they haven't been properly calibrated yet, so we may get quite a bit more power out of them.


Videos:
http://www.youtube.com/watch?v=mlUPGUfgrHo#

http://www.youtube.com/watch?v=crKvPEwvf-U

And for those safety nazis -- why yes we do have a safety cage for it :)

Re: For those who are skeptical about propellers - Team 2526
 

What type of props are those? They look like 9"x something. Are they balanced? If not, I can tell you how to balance a prop.

Also, I'm not quite sure that that cage is going to be enough. I'd put another layer on on top or underneath so that the area of each open area is divided into four areas--if the props do explode, I'm pretty sure they could get through the pictured version. Reducing the open area will also reduce the risks.

Re: For those who are skeptical about propellers - Team 2526
 

Wow that totally is a unique and different propulsion system! I cant wait to see that in actual competition!

I would tend to agree with Eric though, I'd add some more protection to that cage. The cage will protect from reaching hands, but if those props were to ever break, (and going 7000 rpm, they very well might) you dont want blades going flying... I'm not a safety Nazi, I just like being safe.
Overall though, Awesome!

Re: For those who are skeptical about propellers - Team 2526
 

safety cage we are going to use is designed to keep balls outs rather than keeping blade shrapnel in. :ahh:

Re: For those who are skeptical about propellers - Team 2526
 

Cool.

What are the pegs on your rollers? What's the diameter of them? If they are too small, you might have inspection problems.

Re: For those who are skeptical about propellers - Team 2526
 

The inspectors will be looking for both. One piece of prop shrapnel gets through, and <S01> is probably going to be called. Then you have to remove both.

Let's say those are 9" blades going at 7000 RPM. That's C=pi*d=pi*9=28.26" per revolution. That's about a 2' circumference (rounded down to emphasize the need for protection here). So, the tips of that prop are traveling at 7000RPM=116.7RPS over a 2' circle. That's a tangential speed of 233.3 feet per second--or about 4 FRC fields in one second. If a tip breaks off at that speed, you WILL get a safety violation if it leaves the robot! And, if I were the head ref, I'd make you either remove the props or add protection to the cage. Play it safe and add material now.

Edit: I just saw this: http://www.chiefdelphi.com/forums/sh...049#post812049
I would consider this, or something similar, much safer than your current setup.

Re: For those who are skeptical about propellers - Team 2526
 

Nice work, looks like you put some thought into the design. Good use of model airplane props.

Are you worried that having the props mounted in a biased configuration (not dead-center on the robot) will tend to make the robot turn or move awkwardly? I assume you offset them to make room for a ball-handling system. Will the airflow pass through the ball system or will you reverse the rotation to reverse the direction of the robot?

On a separate note, have you checked the metal hardware on your collector to make sure it's not going to rip up the balls? Looks iffy to me.

Re: For those who are skeptical about propellers - Team 2526
 

What you should do is put them up high, so they will both propel your bot and blow-away balls.

If it can move a 120 lb. bot it should be able to deflect a few rocks :yikes:

Re: For those who are skeptical about propellers - Team 2526
 

Sadly that hasn't worked with the tests our team has doen, the porous nature of the ball's geometry tends to not move it at all. Our tests were all done with a 22" blade with a 3D-10A pitch blade that was moving a lot of air at a 1:1 ratio from a CIM. YMMV.

Looking good guys, keep it up.

-Greg

Re: For those who are skeptical about propellers - Team 2526
 

The propellers are perfectly safe as long as they don't exceed their maximum rpm, the rate at which we are spinning them is no where near their maximum rpm (the maximum is about 13k rpm). Having them spontaneously exploding is not a huge concern to us, having balls getting in the way of the props is a much bigger concern. (oh and its 12.25 in in diameter btw ;D)

Re: For those who are skeptical about propellers - Team 2526
 

I'm taking Eric's word on this one.

I highly doubt that the inspectors will give a crap ( or too much) about the safety of the precious orbit balls.

I say that if a finger or even a hand can pass through the cage, then it is not safe.

+$0.02

Re: For those who are skeptical about propellers - Team 2526
 

Yeah, that's why we have a 3.5 multiplier on our props. So the 2.5 k rpms you get on a CIM motor at peak power output you don't have nearly enough pushing power. Our props are actually push them at about a walking pace.

See, ideally you reach 88% - 94% the speed of sound on the tips of your props in order to get maximum power.

Re: For those who are skeptical about propellers - Team 2526
 

Who is dumb enough to stick their fingers in there?? Plus the props are far enough inside the cage that even if you can get your fingers in, they wouldn't touch the props.

PLUS who's running around the field trying to catch a robot by sticking their fingers into the cage with spinning blades???

Re: For those who are skeptical about propellers - Team 2526
 

Pit area? Although safety should always be first, sometimes mistakes are made.

Re: For those who are skeptical about propellers - Team 2526
 

Well, our blade/s pull too much power to gear it up any. We start tripping a 40A breaker at a 1:2 ratio. The size of our prop combined with the really high pitch, and the fact that the blade is cut to give a lot of thrust in one direction.. gave us a pretty good acceleration to around the speed you're describing at 3/4 ratio.

Of course we're going for different things. You have them for turning and maneuvering plus a good amount of power. And we're going for sheer power, mainly for getting across in a straight line fast, pinning, and then dumping.

Tell you what, you make it to Atlanta for Championships, we'll have an Overdrive style race. ;)

-Greg

Re: For those who are skeptical about propellers - Team 2526
 

How about we put safety whistles behind the props so everyone can hear when they're on and uh.. think?

Re: For those who are skeptical about propellers - Team 2526
 

Who's dumb enough to accidentally turn on a robot when someone is working on the blades???

Who's dumb enough to move the wheels when someone is fixing a sprocket on the drive train?????


I can make lots of question marks too. You can get as defensive as you want about your robot design itself, but when it comes to the safety of others don't take suggestions lightly.

If you're not in it for the safety and well being of your members and others in the pit, that's fine by me.

Re: For those who are skeptical about propellers - Team 2526
 

You might want to reduce your pitch then. High pitches are made for high speeds, therefore you're being really ineffective and ideally you'd have about 1-2 pitch prop from max speeds of about 7-15 mph. Otherwise, even with our pitch of 3.75, we hit ideal speeds at about 30 mph.

And yes, prop race at Atlanta ;D

Re: For those who are skeptical about propellers - Team 2526
 

12.25 inches????

Let's run the numbers. That's 374.15 feet per second if something breaks! If a prop breaks, it's going 7, yes 7, FRC fields per second.

As for perfectly safe if they don't exceed maximum RPM, that's all well and good, but R/C aircraft don't hit things. That's the facts of it--if they hit anything, they crash (or just crashed) and the prop is broken anyway. These props are going to be jostled through shock loads when they get hit. This could potentially weaken them. If they're weak, and they get one hit too many, somebody is going to get hit, hard. I haven't run the numbers on KE for, say, 1/3 of a prop, but that's far more than I want to have hitting anybody!

As for who's going to poke hands in, I can think of a few things--little kids, poles from a tipped trailer, unsuspecting students... I am pretty sure I could get my hand in enough to contact at least one prop.

Bottom line, don't worry about keeping balls out, worry about keeping the props in. If you do that (better than the cage shown will), the balls will take care of themselves.

Oh, and I just remembered--if you reverse those blades while they're going full bore, that's a pretty hefty acceleration force you put them through. This will contribute to propeller weakening. They aren't designed to run in reverse.

Re: For those who are skeptical about propellers - Team 2526
 

Yes, the cage does make it more safe, but why isn't it on during testing? In the 2nd video, I think the person bending down gets a little too close; one slip and people will be watching the video for different reasons...

Creative design, but make sure it's safe

Re: For those who are skeptical about propellers - Team 2526
 

I believe the KE for 1/3 of the prop will be over 2000 joules so yeah, it's not something I want to be in front of when it comes flying off.

Re: For those who are skeptical about propellers - Team 2526
 

How about this: We'll put extra thick mesh on the sides of the safety cage because any flying props would.. exit there. But to keep proper airflow, the current cage in the front and back should suffice.

Re: For those who are skeptical about propellers - Team 2526
 

Yup. It is by my account also. (Emphasis mine)

Re: For those who are skeptical about propellers - Team 2526
 

Thick mesh, or a sheet, would probably work. Even if it doesn't fully stop the prop, it'll slow it down to the point where it isn't nearly as great a danger.

Re: For those who are skeptical about propellers - Team 2526
 

Haha. It just looks like I got close, but really, i grabbed it about a foot in front of the props. And as for the cage, we didn't have the mounting brackets completed at the time of testing... and we were anxious. :D

Re: For those who are skeptical about propellers - Team 2526
 

Don't worry. It's double nylon nutted on. :D

Re: For those who are skeptical about propellers - Team 2526
 

I have to agree with Akash and Eric. I wouldn't just assume that common sense will prevent all accidents. Why do you think they put "HOT" warning labels on coffee cups? Or warnings on electrical things, such as hair dryers, not to submerge in water? ... Sometimes things can happen, and there's no reason not to play it safe...

Other than that, very cool propulsion system! I was one of those skeptical about using fans, but it turns out I was wrong and they work great after all!

Good luck at the competition!

- Austin

Re: For those who are skeptical about propellers - Team 2526
 

Even if I wasn't safety captain for my team two years in a row, I would still like to think that safe practices are of the utmost importance in every FIRST member's mind during the season. While this isn't as deep as thousands of people dying, you still need to take some caution in the real world, and all the FRC is doing is preparing you to make safety second nature.

Afterall, we don't want this:
http://www.chiefdelphi.com/forums/sh...ad.php?t=65978

or this:
http://www.chiefdelphi.com/forums/sh...ad.php?t=59436

to sound like something that might happen as a result of your team's machine. I take safety seriously, and hope that everyone else does too. If not, you need to sit back, forget drilling another hole, and think about that.

Re: For those who are skeptical about propellers - Team 2526
 

I would still have finger-proof mesh in the front and back, and possibly even wire the props so that they cannot be turned on with the mesh removed. Never count on "people won't be stupid" as a saftey feature. Take Murphy's law one step further, "Everything that can and cannot go wrong will go wrong."

*From someone who got his finger caught in Vex chain one time too many.*

Re: For those who are skeptical about propellers - Team 2526
 

Remember we are taking into account 1/3 of a propeller. For all of the smashing that could be happening, those props will no doubt be subjected to forces they are not designed for. These abnormal forces will weaken the propeller, causing it to ultimately fail.

Re: For those who are skeptical about propellers - Team 2526
 

Alrighty.. We'll take care of it. We really posted this here for more the propulsion design rather than safety concerns.

Re: For those who are skeptical about propellers - Team 2526
 

Think of it this way: Now we saved you some time, hassles, and [possibly] stitches this season.

Re: For those who are skeptical about propellers - Team 2526
 

I think we all understand that, and it is a great design, don't get me wrong. We just want you to be safe and take these recommendations into consideration early rather than having the safety inspector telling you the same thing a few hours before a match.

Re: For those who are skeptical about propellers - Team 2526
 

I love the design. Great work. I hope you get Xerox creativity for it at the least.

Re: For those who are skeptical about propellers - Team 2526
 

There's a theory that I give to students in the machine shop. Whenever something is moving, look for the "plane of destruction". It's the plane where things go flying when (not if) things go bad. You never want to be in the plane of destruction.

A denser mesh on the sides are a great idea. also, get some of those big "remove before flight" flags and use them and some kind of peg or clip to prevent rotation whenever it's not on the field. (even better, tie them to the cart so you can't lose them).

Re: For those who are skeptical about propellers - Team 2526
 

Excellent idea, this is what combat robots (battlebots) are required to use to safeguard rotating weapons. Physical pins prevent rotation until the robot is in place on the field.

Re: For those who are skeptical about propellers - Team 2526
 

My Aero Design team has a rule: NEVER stand in the same plane as the prop while the engine is a) running or b) about to be started. In front or behind is OK (or required, depending on who you are), but never to the side. Shield the plane of the props, and a little in front of and behind that plane, and you *should* pass inspection. By doing so, you also get a "ducted fan", where there is almost a funnel for air to pass through. These are just as good as unshielded props, if not better.

Re: For those who are skeptical about propellers - Team 2526
 

This is the same rule we have when working on props and jet turbines at the aerospace museum where I volunteer. All of our APUs (jet turbine powered generators) have distinct red lines painted on the enclosures to show the plane of the turbine blades.

Re: For those who are skeptical about propellers - Team 2526
 

I'd have to agree about the ducted fans. Close ducts around the blades SERIOUSLY improve propulsion force because less air is thrown off to the sides because of centripetal force. The duct creates a high-pressure zone around the edges of the blades that focuses all the air from front to back. Not to mention, if you narrow the end of the duct a little (toward the back), you get higher pressure, which should help you to move forward faster.

Insulation foam (like the kind used in insulation board) is very good for fan ducts, as it's easily formed, strong, and light weight, not to mention will catch any flying pieces that should come off in the foam itself, so you don't get any ricochets.

I can see how under normal circumstances that cage should be safe, but think about what could happen if a nut popped off either your robot or another one in a collision (as it looks like you'll be hitting pretty hard!) and fell into the propeller, you've basically got a "low-speed" bullet, probably combined with a shattered propeller blade that is no longer bound by centripetal force. Sure, all the drivers, coaches, and human players (minus maybe the two in the middle) would be perfectly safe behind half-bullet proof glass, but the judges and refs (who give you points, by the way) could be in serious danger. I think spending a couple hours lathing some foam into ducted fans is more than worth it to improve performance and keep people saying, "Dude, that was awesome!" instead of, "Ow. Hey, can I get a -- no, seriously, ow."

SWEET robot though! Really like the numbers on those things, looks like you'll be having some very fun matches at nationals!

Re: For those who are skeptical about propellers - Team 2526
 

It's a great design but IMHO I don't think it will push a 120 pound robot with trailer around the arena. Just my $.02. I'll take our wheels on regolith to move any day.
I do take offence though that just because allot of people have concerns about the safety of the props being call "safety nazis" :mad:

Also, concerning your ball gatherer you may want to look at this rule:

Exterior or exposed surfaces on the ROBOT shall not present undue hazards to the team members, event staff or GAME PIECES. Reasonable efforts must be taken to remove, mitigate, or shield any sharp edges, pinch points, entanglement hazards, projectiles, extreme visual/audio emitters, etc. from the exterior of the ROBOT. All points and corners that would be commonly expected to contact a GAME PIECE should have a minimum radius of 0.125 inches to avoid becoming a snag/puncture hazard. All edges that would be
commonly expected to contact a GAME PIECE should have a minimum radius of 0.030 inches. All of these potential hazards will be carefully inspected.

* gets off soapbox and puts on flame suit :ahh:

Re: For those who are skeptical about propellers - Team 2526
 

Interesting

Re: For those who are skeptical about propellers - Team 2526
 

I've always known that closed ducts increases thrust (thanks mythbusters :D ) but have never known how proceed in making them. Thanks for the suggestion on how do make that possible.

Re: For those who are skeptical about propellers - Team 2526
 

Just keep in mind that the same rules of production apply here as do in MythBusters, i.e. there will be foam everywhere wherever you do this. I would recommend getting layers of foamboard and cutting out circles close to the end diameter with a knife, and then shaving off the remaining parts as close as you can. Then glue the layers together as closely lined up as possible (epoxy/gorilla glue works well), let cure, and then take some sandpaper to the inside to get it perfectly smooth. Make sure that the inside diameter is NO MORE than 1/4" off the tip of the blade, and that's REALLY pushing it. Try to get it about 1/8" if possible. This is the easiest way I know how to do it, it'll be really friggin' strong, and it'll look pretty cool. Make sure to put a grating on both the front and the back that fingers cannot penetrate at all and will resist nuts and screws. If it ends up looking dorky, you can always put some LED's inside the foam to light it up into a cool blue (as the foam is already blue).

Re: For those who are skeptical about propellers - Team 2526
 

very cool design, but i beleive steering could be an issue, but heck with that it will still be the most recognized bot at any venue. I know I would be leaving the pit area to watch you fire that thing up.

Re: For those who are skeptical about propellers - Team 2526
 

Wow, one foot! That's a safe distance. Two weeks ago in response to safety concerns you said:
After the safety advice you received over the last two weeks ago, you're now educated enough to make the following comments
It's pretty obvious that you guys are a team of know-it-all invulnerable teenagers without adult supervision, never mind engineering mentors. Many people have tried to point out the safety issues and like all Darwin candidates you smugly dismiss them with flippant comments.

I don't expect that you will change your ways and since children, drunks, and idiots are often protected by providence I expect you'll survive without incident. I also expect that if you show up with anything like your present wire cage, you'll be promptly thrown out of the pits.

But you do provide a service that draws useful advice that less arrogant individuals may use to reduce the risk that their machines pose to themselves and any onlookers. By the way, here's one example of what can go wrong:

http://www.youtube.com/watch?v=hmcTyBxSL00

The R/C hobby has a pretty good safety record over the years, although it is not been free of de-capitations and other fatalities and many serious injuries. There are no perfectly safe propellers and no perfectly safe anything for that matter. It's a matter of understanding risks and reducing them to acceptable levels. Mostly, this happens by eliminating "UNNECESSARY" risk and you guys are a shining example of those.

Every decade or so, something changes (like mass, blade dia, rpm's, etc) and accidents skyrocket until best practices change.

Do the math. The risk potential comes from the velocity and energy of the parts when they fail and fly. Yes, the propeller arc and thrust line are the most dangerous in the open, but the blades can bounce off obstructions and continue in any direction. Vibrations and flutter can cause rapid failures. A foreign object sucked into the airstream can damage the prop or cause an immediate blade failure, especially if it impacts near the tips. Given this years robot collisions, failure modes not encountered in R/C flying can be expected. Anything short of full containment just isn't going to cut it.

Few of those who loose fingers or suffer other serious injuries intended to do so.

FIRST has a safety culture for very good and valid reasons. If you are unwilling to accept that culture and consider those looking out for your safety and that of the public to be Nazi's, then you are of no benefit to the FIRST program.

Re: For those who are skeptical about propellers - Team 2526
 

writchie beat me to the rant post about how ignorant you're being.

The idea is cool, yes. You need to keep in mind though you have some of the most respectable people on Chief Delphi telling you about what you're doing wrong, and you're just shaking off like "oh yeah we'll fix that"

Inspectors will stop you if your props look remotely unsafe. They're looking out for everyone's safety not just how cool your robot is. If a 12 year old can put a finger inside your guard, they'll rule it unsafe, judging by that picture I think a 12 year old could fit his whole arm in there.

Re: For those who are skeptical about propellers - Team 2526
 

What's the over/under on the number of propeller robots on Einstein?

Any takers?

Re: For those who are skeptical about propellers - Team 2526
 

0/6

Sorry 1771...I still love you guys.

Re: For those who are skeptical about propellers - Team 2526
 

1/6 at best

Re: For those who are skeptical about propellers - Team 2526
 

Awe come on Akash. This is our year to make it. I'm feeling it in my bones...now if we can just get our bots finished we might actually have something. :D

Re: For those who are skeptical about propellers - Team 2526
 

I wouldn't be surprised if FIRST issues guidelines regarding safety measures for propellers (just remember the guidelines for last year's catapults). FIRST is (and should be) risk adverse when it comes to safety.

As an inspector, I'm going to ask a lot of questions about the safety provisions and considerations in high-energy, potentially lethal features in robots.

What margin of safety do you have in the hazard containment? (Prove to me that you've got at least a factor of five in keeping all parts from penetrating your safety shields.)

How do you verify that there are no flaws in the propeller and attachment components? Do you have proof of inspection for cracks in the propeller, shaft, etc.? Do you have safety-wired fasteners and a fail-safe design (i.e., if a fastener fails, do you still have margin against catastrophic failure)?

Sound tough? This is nothing compared to the aftermath of a failure where someone is seriously injured or worse.

Re: For those who are skeptical about propellers - Team 2526
 

I was thinking, what if there was a way for teams to have a touch sensor near their fan mounts, like really really really close, so that if the propeller moves even like .125" from its original mounting position, the motors to the fans shut off when the limit switch or touch sensor is touched? Seems simple enough to me.

Re: For those who are skeptical about propellers - Team 2526
 

I had the same thought, my afterthought though was teams that would take this precaution would probably have very good safety precautions already for any other situation.

Re: For those who are skeptical about propellers - Team 2526
 

A 12 inch prop rotating at 7500 RPM has a wing tip speed of about 120 meters per second. It stores considerable energy. Even if you could anticipate ALL of the possible fault scenarios and detect when they occur, removing the energy source is not going to change the mechanical energy much over the short term. It's too late to have any effect.

IMHO The only realistic measures are distance from the hazard (used in R/C flying) and containment and only the latter is available to us. For the containment scenario, I think that teams will have to demonstrate that their containment materials and configuration can easily contain a prop failure at max RPM.

There are tradeoffs. Using steel mesh wire, the open area drops dramatically as you increase wire size and reduce mesh spacing. Engineering a mechanism that is both effective and safe is a challenge and either one without the other is just not acceptable.

Re: For those who are skeptical about propellers - Team 2526
 

All safety considerations aside...

Have you done any performance testing as compared with a standard kitbot drivetrain? How about one with some basic traction control?

I'm not overwhelmed by your performance videos, and I'm curious why your team made the design decision to go this direction. Was there testing or prototyping involved? All about theoretical calculations? None of the above?

If the decision was all about "cool factor" then... rock on.

However, if you believe this has higher performance than using those CIMs in the traditional "rubber meets the road" way, I'm curious why you believe so, and if you have supporting data. If you DO have supporting data, I'd absolutely LOVE to get a peek. :)

Enlighten a man who sometimes has difficulty understanding why others stray outside the box, when the box appears to be an optimized and elegant solution. ;)

-John

Re: For those who are skeptical about propellers - Team 2526
 

fixed.:P

I'm curious on your reasoning also, the main reason I dismissed propellers was not only safety, but slowing and stopping. How well does it stop and change direction to reverse?

Re: For those who are skeptical about propellers - Team 2526
 

Theoretically, we're supposed to be getting 30-some newtons of thrust from the current arrangement... and with the calculations (which i long forgot) it was supposed to be able to accelerate faster than bots that use standard wheel drive. However, I emphasize that this is not the final arrangement -- we should have standard triblade props delivered this monday with a pitch of 4, and furthermore, if we get more thrust out of that, we'll try to custom order triblabe or quadblade props with a pitch between 1 - 2, idealizing our max speed (at around 7-15 mph) while boosting rpms and increasing power. THEN, with the addition of a duct (ideally, increasing power by an addition 5%) we should be operating at pear conditions.

Also, the idea of hybridizing our bot has came up: i.e. powering the back two wheels for extra acceleration. Although that's a ton of power stress on the battery, the 3rd CIM for the powered wheels would only work during acceleration, so we should be alright. =)

Re: For those who are skeptical about propellers - Team 2526
 

Ok, My thought: I know this is probably asking alot...But could the regionals have walls along the perimeter to protect the crowd? I don't mean to be overly cautious, but I think I'd feel a little uncomfortable sitting in the crowd while some of the possible bots are going to be running. I'm not asking for anything too fancy. Perhaps just a wall like there is between the drivers and the field. I know, props could easily go over this, but at least it would cut out the worst case scenario.

Otherwise, a cool design. Good luck with the competition. And I hope nobody gets hurt.

Re: For those who are skeptical about propellers - Team 2526
 

Or FIRST could just solve the problem directly and not allow unsafe robots to compete

$0.02

Re: For those who are skeptical about propellers - Team 2526
 

Should be fine. If you'll be at the Portland regional, I'll have a Kevlar helmet you can borrow, as well as glasses capable of withstanding a shotgun's deerslug at 5m. (Yay ROTC!)

I honestly don't want to see FIRST turn into battlebots, where the field is contained by walls. It blocks viability, and makes the competitions ugly and slow due to access.

Re: For those who are skeptical about propellers - Team 2526
 

Only thing. Just because FIRST says it safe, is everyone going to make the same ruling? For instance: We've all seen those "smart" cars. They are ruled to be safe. However, I will never drive one. I just wouldn't feel safe, regardless of whether or not I am. You have to remember when it comes to safety, apparent safety is close to the same importance of actual safety.

Re: For those who are skeptical about propellers - Team 2526
 

Time for my two cents...
I am a lead inspector, and yes I am concerned about the safety of anyone at any time. This includes participants, volunteers, camera people (many of whom I know), judges and refs. If that makes me a Safety Nazi then I can live with that label. I am concerned about safety when your robot is in your pit, on the practice field, on the competition field or anywhere in between. Pits are crowded places in which I spend a lot of time and I have seen things over the years that curdle my blood. First is about innovation and creativity in design and we should encourage those ideals for the betterment of the program, but not at the loss of other equally important ideals such as safety. We have low voltage power sources for your safety, electrical rules for your safety and pneumatic rules for your safety. Expect inspectors to take a close look at your designs not only for safety but I would be prepared to show accoustic output as well. Should the GDC issue guidelines for prop driven robots we will follow those guides explicitly. Until then good luck with your development.

Re: For those who are skeptical about propellers - Team 2526
 

I really think you guys believe that props are bound to spontaneous explode or something. As long as balls or anything of a significant mass does not touch them, there is no reason for them to catastophically fail. We'll most likely be replacing props after every round / two rounds, just to rule out any failure chances due to wear. Beside that, I believe any other precautions are just silly. I mean, I trust the machine... I stand a foot away from it while it's on. Idk if others trust my contruction, but i sure know i do.

Re: For those who are skeptical about propellers - Team 2526
 

Our robots have never had props on them and I'm always more than a foot away from them while they are on unless they are propped up on blocks.

I can't say I understand why your blatant disregard for the safety advice posted by members with experience with these systems means that I should trust your robot to be safe.

If this robot manages to pass inspection with the safety cage shown in those pictures, I will be instructing my team to at the very least put on safety glasses in the stands every time your robot is on the field.

Re: For those who are skeptical about propellers - Team 2526
 

Have you ever been to a competition? After each match you will see various parts from the robots on the floor. What if a bolt or nut was to be flipped into your props.Even if they didn't damage your props where does the part go after hitting the props.
Also, on a safety note. In your videos it shows your robot going along the floor PAST all the students with uncage props. When I'm around running R/C aircraft I NEVER put myself in the plane of rotation. I've seen first hand what a prop can do if it breaks and flies free. I've seen them imbed themselves into 2x4 park benches.
PLEASE BE SAFE!!!!!

Re: For those who are skeptical about propellers - Team 2526
 

I'm not blatantly disregarding, I'm taking them into consideration and adding just enough safety features so that the props can still function.
We will upgrade the cage, in particularly in the 'plane of destruction'.

And really, say a prop was coming at you, I wouldn't be that concerned about my eyes, but rather, other parts of my body. Becuase theoretically (depending the mass of the fragment ofcourse), you'd get some penetration in the skin if that hit you. And then... surgeons would have fun dislodging a 'plastic knife' from your body. Not really the best image, but.. atleast you'd be able to see your own masacre. [sorry for the sarcasm, I'm just a little angry about our progress XD]

Re: For those who are skeptical about propellers - Team 2526
 

Yes. Debris would be an interesting encounter. I'm thinking of loosing the set screws on the gears just at the point of slipping. Then if there is any added resistance [ideally] the prop would simply slip through and maximum damage could be eliminated.

Re: For those who are skeptical about propellers - Team 2526
 

It won't be spontaneous, it'll be in response to a large object passing through your porous safety cage and into the props. Maybe an orbit ball will come apart above your bot and the plastic shards will fall on your bot. Maybe another team's robot will shed bolts, or maybe a human player will accidentily toss their watch. Maybe a wire will break or come loose and will get ingested. Maybe a robot will fall on your cage and bend it inwards, hitting the prop.

Also keep in mind that every time your robot hits a wall or another robot at speed, your props will endure forces well beyond what a normal R/C plane ever encounters. An impact with the wall may decelerate a bot at 10gs, which means your fast-spinning props have to deal with that deceleration and not vibrate themselves to death. An R/C plane never sees accelerations like that.

If you don't want to change your design on safety grounds, not believing that it is a risk, change it based on pragmatic grounds: despite any "no that won't happen" arguments from your team, inspectors will mostly likely not permit your robot to compete. So even if you don't personally believe it is a safety risk, it seems that pragmatism would compel you to make a better safety cage.

Re: For those who are skeptical about propellers - Team 2526
 

Two words. ducted fan.
Bruce

Re: For those who are skeptical about propellers - Team 2526
 

I've already mentioned that we'd construct a better cage. I'll get pics of it up as soon as possible just to stop all these continual scoldings. XD

Re: For those who are skeptical about propellers - Team 2526
 

I can think of all kinds of examples of things that "should" not happen that end up happening. I know in the chemical industry and know in others, things are designed to account for failure scenarios. Why? Because it will happen at some point. That is why people spend weeks doing things like a Layers of Protection Analysis and Failure Modes Effects Analysis for big projects. Do you need to spend weeks doing that? No, this is much smaller, but spending a few hours thinking about things that could go wrong would not be amiss.
Listen to Al, a lead inspector. Listen to all the others who have years of experience both with FIRST and in industry. If it is anything to you, I will be inspecting teams at your regional on Thursday and reffing on the field on Friday and Saturday.
I like that you are thinking of changing the fans and making a better cage. Just remember, the folks on here are trying to help you so that you don't have to scramble on Thursday at the regional.

I think it is an interesting design. I will withhold judgment on it until I see it in action.
Good luck to you!

Re: For those who are skeptical about propellers - Team 2526
 

As stated before, we're all inspectors, spectators of horrible accidents, or Safety Captains, that just want to make sure you (and the event attendees) stay safe. I truly hope that you change your view on the safety procedures of your team.

Hopefully your team has a competent safety captain, good practices for your heavy (and light, for that matter) machinery, procedures to deal with an accident (should one occur), etc. It looks like a great design, very innovative, but remember: Safety FIRST!

Re: For those who are skeptical about propellers - Team 2526
 

I encourage your team to take a look at this post:

http://www.chiefdelphi.com/forums/sh...threadid=73389

That is the kind of safety precautions that are necessary. More fencing to keep fingers and smaller parts out, and extremely safe plane protection.

Also I would like to note that all of us here at FIRST truly believe in the ideals of Safety and GP. Not just as a way to get an award. If these ideals are ignored by anyone the competition breaks down at it's core. I encourage you to visit a local senior team and check out their safety procedures, our you can email me at xanderjanz@gmail.com to find out about 1458's safety procedures. This is no joke and we expect you to take safety seriously.

Re: For those who are skeptical about propellers - Team 2526
 

Good, intresting design, but i have one question. Isn't there a rule about the wheels being parallel to each other? In the one picture you can clearly see how the frontwheels turn with the propelers while the back wheels just stay stationary. Is this still legal? From how i read it and heard, it doesn't seem legal.

Re: For those who are skeptical about propellers - Team 2526
 

You're thinking of <R06>, which specifies that the axis of rotation of the wheel must be parallel to the floor. It doesn't say anything about the axis of rotation of the axis of rotation.

Re: For those who are skeptical about propellers - Team 2526
 

There's a rule about the wheels being perpendicular to the floor...I don't know about any rule saying they can't steer.

Re: For those who are skeptical about propellers - Team 2526
 

ok, thank you. I was just a little confused.

Re: For those who are skeptical about propellers - Team 2526
 

Zrop,

It's not your design we're bashing. The design is really cool. It's that you seem to blow people off with a flippant comment every time someone mentions safety. Everyone wants to have a blast at FIRST but we also want to go home to our families intact. Therefore safety is huge. It especially concerns those of us who know things can go wrong even when you are being safe. That's why "trusting a robot" is a scary thing. I've been in and around FIRST for 13 years now and I still wouldn't "trust a robot" when it comes to my own personal safety. Just think about it.

Re: For those who are skeptical about propellers - Team 2526
 

On military aircraft carriers, twice a day or more all members of the crew stop all operations to perform a FOD (Foreign Object Disposal) walk, in which they walk shoulder to shoulder across the flight deck looking for any foreign object as small as 1/8" in diameter. This is to prevent the disasterous consequences that could result if one of these objects were sucked into a jet intake or blown around by jet exhaust or prop wash. Keep this in mind as you work on your systems.

Re: For those who are skeptical about propellers - Team 2526
 

I think this is a good idea, but i have one question, won't using propellers make stopping harder?

Re: For those who are skeptical about propellers - Team 2526
 

Not if they quickly pivot 360 degrees ;D

Re: For those who are skeptical about propellers - Team 2526
 

Nice :D

Re: For those who are skeptical about propellers - Team 2526
 

But how will they rotate quickly if they move with the steering of the wheels?

Re: For those who are skeptical about propellers - Team 2526
 

Look up rotational inertia. It would seem the laws of physics do not agree with you on this stopping method. Good luck on trying to find a different way of stopping.

Re: For those who are skeptical about propellers - Team 2526
 

Rotational inertia. As said before the props aren't intended for anything more than spinning and moving an R/C plane. The vibration from the robot is already more forces than intended, let alone the sudden accelerations from crashes, and now rotational inertia. You should really start rethinking some of these issues. You're making it seem like this is all a joke and you're just shrugging off every suggestion. I think most people reading this thread have the same mindset that that's what you're doing with every single one of our posts.

Re: For those who are skeptical about propellers - Team 2526
 

If you have no experience with this force (i didn't until last year) spin a wheel on a rod then try to rotate it like you would the props. You get very interesting results

Re: For those who are skeptical about propellers - Team 2526
 

Yeah I'm really concerned about the gyroscopical effects of the props. But hey, I've seen videos of hovercrafts using rotating prop bases, so i think it's feasable. We're going to figure out controlling this stuff this week, so we'll get back on the results. XD

Re: For those who are skeptical about propellers - Team 2526
 

Alternatively, the motors could be thrown in reverse. The problem with that though is that the leading edge of the props would become on the wrong side, greatly decreasing thrust.

Re: For those who are skeptical about propellers - Team 2526
 

If you are using the Jaguar I would recommend you use the limit switch function to prevent a change in direction. If using a Victor, install a line in software to prevent counter rotation.

Re: For those who are skeptical about propellers - Team 2526
 

I hope you appreciate that the comments and concerns about the safety of your propellers is HELP from the CD community. I know several teams have given this approach serious consideration (including our team).

Team 980 chose an alternative drive concept, not because of safety concerns with fans, but for performance needs to support our game strategy. We felt we could contain a failed propeller and avoid having debris getting sucked in and becoming a dangerous projectile by using a "ducted fan" approach with steel mesh over the ends. I don't think your robot can detect a problem with your props and react fast enough to insure no shrapnel will be produced. It's better to have a design which is not going to allow anything dangerous to escape. With the ducted fan, you'll get better thrust performance as well.

I look forward to seeing videos of your robot on the move!

Re: For those who are skeptical about propellers - Team 2526
 

Why would this be necessary??

Re: For those who are skeptical about propellers - Team 2526
 

The limit switch function of the Jaguars is off limits this year (by rule, see Q&A). You may not use them. The jumpers must remain in place

Re: For those who are skeptical about propellers - Team 2526
 

Perhaps the glasses would withstand a 12-gauge deerslug, but your face behind them won't. Just saying...

Re: For those who are skeptical about propellers - Team 2526
 

What is this 'limit switch function' you refer to?

Re: For those who are skeptical about propellers - Team 2526
 

Confirmed, maybe.
Here is the quote from the Q/A:
The problem is, <R62> is about the Solenoid breakout board, not the limit switch inputs on the Jaguars.
<R61> Talks about the CAN Bus, but also does not limit the use of the limit switch inputs.
So, not trying to be contrary to the GDC's responses, just exactly where in the manual does it specifically rule out the use of the limit switch inputs??
I would ask this question myself of the GDC, but I do not have permission to post on the Q/A forum, only read.

Re: For those who are skeptical about propellers - Team 2526
 

Martin,
I was just asking myself the same thing. I think there may be confusion between the CAN bus and the limit jumpers. BTW, I did not see the Q&A response.
Second, please disregard Rev F there were errors now superceded by Rev G.

Re: For those who are skeptical about propellers - Team 2526
 

Re: For those who are skeptical about propellers - Team 2526
 

I just took my own advice and re-read <R61>. I now see why the answer is as it is. Their original post was mentioning <R62>, it has now been corrected.

I concur, Limit switch input is off limits via the Jaguar. See the BOLD section of the <R61> quote above. It shows the answer.

Re: For those who are skeptical about propellers - Team 2526
 

Make sure you are looking at the latest rev of the manual and the latest rev of the question. They were out of sync for one rev due to a numbering problem (thank you, Microsoft). But that seems to have now been addressed and corrected. The Q&A answer appears to be pointing to the correct rule, as correctly numbered (again) in the manual.

-dave



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Re: For those who are skeptical about propellers - Team 2526
 

This just in, Dave Lavery is a Apple supporter. Spread the word.