For those who are skeptical about propellers - Team 2526

[zrop]

Originally Posted by rocketperson44

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.*

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

[synth3tk]

Originally Posted by zrop

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

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

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.

[Akash Rastogi]

Originally Posted by zrop

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

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

[engunneer]

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).

[Woodworker88]

Originally Posted by engunneer

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).

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.

[EricH]

Originally Posted by engunneer

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.

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.

[Woodworker88]

Originally Posted by EricH

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.

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.

[daltore]

Originally Posted by EricH

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.

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!

[Wayne Doenges]

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"

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

[Sean Raia]

Interesting

[Koosley]

Originally Posted by daltore

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!

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

[daltore]

Originally Posted by Koosley

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

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).

[Team2883]

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.

[writchie]

Originally Posted by zrop

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.

Wow, one foot! That's a safe distance. Two weeks ago in response to safety concerns you said:

Yeah I agree with what you said. We just rushed to mount the prototype in order to disprove any skepticism our team had. So inevitably, safety was the first thing that was overlooked... Atleast everyone wore safety glasses...

After the safety advice you received over the last two weeks ago, you're now educated enough to make the following comments

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

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

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

...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)
Reply With Quote

...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.

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

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

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.