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  #121   Spotlight this post!  
Unread 26-11-2012, 12:25
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Re: Be afraid... Be VERY Afraid

1. There are two advantages that we have seen so far. The first is a serious weight reduction as we don't need AM shifters. Also the ball will be made of carbon fiber wrapped in some undecided traction material. We also get a bit more friction if we were lets say trying to be pushed by another robot. This is due to the fact that we can put the driving wheels perpendicular to the incoming force, thus allowing the friction between the ground and the ball as well as the driving wheel and the ball. The second advantage is that we can easily disengauge the ball completely and use it as a "castor wheel".

2. LabVIEW. We have written some preliminary algorithms for the basic driving. We are now working on automating some maneuvers.

3.We still haven't decided on the exact cylinder, but will most likely use the tiny cylinder in the KOP (I can't remember the bore size). It will be mounted on a pivot point at an angle from the floor to the right of the big drive wheel.

4. We are aiming at less than 3 lbs (without including the CIM). This will depend on what materials we use (carbon fiber, aluminum, titanium). It will be a modular plugin to the chassis.

5. I have taken this into consideration, so in response, we will only be using this system if it is successfully running in a fair amount of time.
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Unread 26-11-2012, 12:41
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Thumbs up Re: Be afraid... Be VERY Afraid

It looks like this ball is only powered on one axis. In that case, why a ball and not a wheel?
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  #123   Spotlight this post!  
Unread 26-11-2012, 12:49
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Re: Be afraid... Be VERY Afraid

Cool! Thanks. Followups:

1A. I'm missing how you get "more friction". Isn't the first place you slip the only one that matters? I guess I'm not understanding what you intend to do (in part because of Chris's question).

1B. What's the benefit of turning it into an caster wheel in this setup?

4. Wow, 3 pounds? Keeping that in-cost is definitely impressive. What's the ball diameter?
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Unread 26-11-2012, 12:49
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Re: Be afraid... Be VERY Afraid

Again due to the weight reduction advantage. The module its self is able to rotate 360 degrees to give the swerve effect. Also this whole project is a way for us to satisfy our engineering curiosity and out of the box thinking.
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  #125   Spotlight this post!  
Unread 26-11-2012, 12:56
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Re: Be afraid... Be VERY Afraid

Siri,

1. You are correct in that the first place that you lose friction is the only one that matters, but since there are multiple contact points, each one adds to the total friction available. Lets suppose you see an incoming robot front the right of our robot, we would turn the wheels so that they face front to back (perpendicular to the incoming force).

2. It would simply be used as a built-in neutral position which may or not help with this years game.

3. I believe the diameter is about 4 inches.
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  #126   Spotlight this post!  
Unread 26-11-2012, 13:05
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Re: Be afraid... Be VERY Afraid

Maybe I'm a cynic, but until this design gets the Aren Hill Seal of Approval (or at least his thoughts), I dunno that I'd put it on the field during the season. Aren has more experience with different/non-standard swerve designs than any single person on these forums. OP, I'd message him specifically if I were you.

Also, post the overarching design as a Photo to get more/better feedback -- the veterans on these forums tend to write these types of threads off as more chatter when sifting through the noise. "Be VERY Afraid" will not get you a whole lot of constructive feedback on a technical design.

Presentation aside, it definitely looks interesting.
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  #127   Spotlight this post!  
Unread 26-11-2012, 13:07
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Re: Be afraid... Be VERY Afraid

Beautiful CAD! But the concept I'm a bit skeptical about. What happens if your robot is hit really hard? Can the ball become dislodged? It looks like you are relying on gravity and the wieght of the robot to actually hold it onto the ball. What if your Robot CG is higher and your drive ball becomes a part of the field accidentally?

Thats what I see.

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  #128   Spotlight this post!  
Unread 26-11-2012, 13:09
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Re: Be afraid... Be VERY Afraid

1) I can see a couple of problems here. First of all I'm not sure you can get as much traction on that ball as you would wish. The common matertial that I would think of using to cover the ball is roughtop. However roughtop's performance on carbet is directly related to how much tread is touching the carpet. Second the locking system that you described can be done with a regular swerve. However with a regular swerve it is mechanically impossible for the wheel to roll, so you will have a greater resistance to being pushed. Also this whole setup is less efficient. Lastly you usually don't want castor wheels. In this setup specifically you will lose motor power. However I could see them being useful maybe on the bridge this past year.

4) A pound or two more it seems like you could do mini modules like 1625 did. This setup would be much more efficient than your current one, and for the performance gain it would probably be worth the weight. Try getting modules as small as possible. I have done it and it is a very interesting design challenge.
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  #129   Spotlight this post!  
Unread 26-11-2012, 13:16
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Re: Be afraid... Be VERY Afraid

Quote:
Originally Posted by bhumudar View Post
1. You are correct in that the first place that you lose friction is the only one that matters, but since there are multiple contact points, each one adds to the total friction available. Lets suppose you see an incoming robot front the right of our robot, we would turn the wheels so that they face front to back (perpendicular to the incoming force).
I think the way you are wording this statement is misleading. Siri's statement that you reiterated is very important- whatever slips first is the limiting factor.

I believe I understand what you are saying, that by moving the wheels perpendicular to the incoming force, you are using the traction of the ball and floor as your traction limit as opposed to the traction limit on the wheels against the ball. What is hanging me up is the part where you say "each one adds to the total friction available". This is not a summation, your maximum theoretical resistance to pushing (or traction) will be limited by the ball's traction with the floor.

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  #130   Spotlight this post!  
Unread 26-11-2012, 13:20
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Re: Be afraid... Be VERY Afraid

Quote:
Originally Posted by Brandon Holley View Post
I think the way you are wording this statement is misleading. Siri's statement that you reiterated is very important- whatever slips first is the limiting factor.

I believe I understand what you are saying, that by moving the wheels perpendicular to the incoming force, you are using the traction of the ball and floor as your traction limit as opposed to the traction limit on the wheels against the ball. What is hanging me up is the part where you say "each one adds to the total friction available". This is not a summation, your maximum theoretical resistance to pushing (or traction) will be limited by the ball's traction with the floor.

-Brando
Wouldn't it then be the: ball traction - wheel traction = Max. Theoretical Traction.
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  #131   Spotlight this post!  
Unread 26-11-2012, 13:22
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Re: Be afraid... Be VERY Afraid

Doesn't a sphere give you a disadvantage as far as friction is concerned?

In a perfect spere only one point would be tangent to the ground.

In a wheel, the entire width of the tread is touching the ground.

Am I missing something?
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Unread 26-11-2012, 13:25
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Re: Be afraid... Be VERY Afraid

Quote:
Originally Posted by Saberbot View Post
Doesn't a sphere give you a disadvantage as far as friction is concerned?

In a perfect spere only one point would be tangent to the ground.

In a wheel, the entire width of the tread is touching the ground.

Am I missing something?
Regularly your traction is based on weight and COF. However with roughtop the tread locks into the carpet so this is ture.
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  #133   Spotlight this post!  
Unread 26-11-2012, 13:26
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Re: Be afraid... Be VERY Afraid

I would not have guessed this... thought it was a re-imagining of the Nonadrive corner module... though, I'm a pretend engineer and THAT'S my excuse...

QUESTION: I don't see anything that leads to structure that holds the chassis up? Where's the shaft that this spins around on that will support the weight of the robot?

I'm assuming the shaft will be on the top-side of what's shown so far... or, are you going with a "Lazy Susan" on top with this fastened underneath and attached with standoffs (like the large gear below)?
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  #134   Spotlight this post!  
Unread 26-11-2012, 13:59
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Re: Be afraid... Be VERY Afraid

Hrmp. My delete button is broken.

Last edited by Tom Line : 26-11-2012 at 14:17.
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Unread 26-11-2012, 14:03
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Re: Be afraid... Be VERY Afraid

Quote:
Originally Posted by bhumudar View Post
The module its self is able to rotate 360 degrees to give the swerve effect.
What's the full weight of the unit (with swerve)? And what leads you to believe the ball system will be lighter than using wheel?

Quote:
Originally Posted by bhumudar View Post
You are correct in that the first place that you lose friction is the only one that matters, but since there are multiple contact points, each one adds to the total friction available. Lets suppose you see an incoming robot front the right of our robot, we would turn the wheels so that they face front to back (perpendicular to the incoming force).
Do you propose that the system will begin slipping between the ball and the rollers or between the ball and the floor? (Why?) I think Brandon and I are both stuck on how aligning the rollers increases this threshold vis a vis a system that doesn't use a frictional drive for steering (i.e. a belt, chain or gear swerve).

And listen to Jesse; you really want to talk to Aren.


Tom: secret's out. OP should probably edit the original post.
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Last edited by Siri : 26-11-2012 at 14:09. Reason: read Jesse's post
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