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Unread 02-01-2009, 01:30 PM
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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.

Last edited by Andy L : 02-01-2009 at 01:40 PM.
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Unread 02-01-2009, 03:59 PM
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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?
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Unread 02-01-2009, 04:46 PM
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Re: For those who are skeptical about propellers - Team 2526

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Originally Posted by SlimBoJones View Post
What's the over/under on the number of propeller robots on Einstein?

Any takers?
0/6

Sorry 1771...I still love you guys.
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Unread 02-01-2009, 04:51 PM
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Re: For those who are skeptical about propellers - Team 2526

Quote:
Originally Posted by SlimBoJones View Post
What's the over/under on the number of propeller robots on Einstein?

Any takers?
1/6 at best
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Unread 02-01-2009, 05:00 PM
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Re: For those who are skeptical about propellers - Team 2526

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Originally Posted by Akash Rastogi View Post
0/6

Sorry 1771...I still love you guys.
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.
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Unread 02-01-2009, 05:18 PM
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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.
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  #52   Spotlight this post!  
Unread 02-01-2009, 05:23 PM
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Re: For those who are skeptical about propellers - Team 2526

Quote:
Originally Posted by David Brinza View Post
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.
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.
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Unread 02-01-2009, 05:25 PM
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Re: For those who are skeptical about propellers - Team 2526

Quote:
Originally Posted by Akash Rastogi View Post
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.
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.
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Unread 02-01-2009, 06:51 PM
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Re: For those who are skeptical about propellers - Team 2526

Quote:
Originally Posted by Akash Rastogi View Post
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.
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.
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Unread 02-01-2009, 07:16 PM
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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.

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Unread 02-01-2009, 07:21 PM
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Re: For those who are skeptical about propellers - Team 2526

Quote:
Originally Posted by JVN View Post
"plastic meets the road"
fixed.

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?
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Unread 02-02-2009, 12:11 AM
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Re: For those who are skeptical about propellers - Team 2526

Quote:
Originally Posted by Andy L View Post
fixed.

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?
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. =)
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Unread 02-02-2009, 12:53 AM
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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.
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Unread 02-02-2009, 12:58 AM
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Re: For those who are skeptical about propellers - Team 2526

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Originally Posted by Molten View Post
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.
Or FIRST could just solve the problem directly and not allow unsafe robots to compete

$0.02
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Unread 02-02-2009, 01:00 AM
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Re: For those who are skeptical about propellers - Team 2526

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Originally Posted by Molten View Post
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.
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.
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