More Wheels?
 

:confused: Can you add a 5th moon wheel that would lower down and still be counted as one of the wheels to the bot and used as a break affect?

Re: More Wheels?
 

You can add as many wheels as you want as long as you follow the rules regarding how wheels are placed.

Enjoy.

Re: More Wheels?
 

And as long as it is the rover wheels, only the rover wheels can touch the floor surface this year.

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Although, if you expect physics to apply to your robot, you might as well lock up the wheels that already touch the ground, because dragging more locked wheels across the ground isn't going to do anything for you.

Re: More Wheels?
 

In 2002, 624 made a robot with a 5th high traction wheel in the middle of the robot for pushing/shoving during the game. I don't have a picture of the robot but it was a beast. If anyone has a picture I would love to see that robot again!

I'm not sure that the 5th wheel will help you since you would be dividing your normal force by 5 wheels instead of 4 wheels.

A 5th wheel helps with traction when you have carpet but not with FRP !

Re: More Wheels?
 

Actually Im not sure if thats true... Yes you would be dividing the normal force by 5 and thus the force of friction remains the same, but friction is not the only thing that needs to be considered. Traction would increase due to more surface area, and thus it would stop quicker.

Yes a 5th wheel is legal, and yes it would probably help a little. I would recomend if this would only be for breaking, mount it perpendicular to the other wheels rather than parallel. The coefficient of friction is higher for the wheels sliding laterally than in line with the rotation, so you would get more friction and stop even quicker.

Re: More Wheels?
 

You don't really get any more traction with 5 vs. 4 wheels.

Surface area is not part of the equation.

From our friends at Wiki -

Re: More Wheels?
 

To emphasize this, it's important to note the differences between this year and previous years. In the past, the wheels were slightly squishy, as was the carpet. As you powered your wheels, the carpet and wheels were able to conform a little, and provide a larger surface area and more grip do to the deformation in the parts. More wheels, therefore, would provide an increase in traction.

This year, the Regolith material is firm and slightly bumpy, while the wheels are firm as well. What this means is that each wheel is going to approximate a point contact with the surface, with no deformation of parts. the conditions the GDC has provided us as closely match the ideal friction equation posted above - where number of wheels does not change the robots traction (assuming all wheels are driven).

Re: More Wheels?
 

What about have six wheels but only have four driving wheels? Will that have better traction?

Re: More Wheels?
 

People will debate, and you won't get a straight answer most of the time. But, here is my take, more wheels doesn't matter (trust wikipedia).
This only applies if all the wheels are powered.

So, if you have two unpowered wheels, the weight on those wheels won't be providing extra traction to your drive train. So, as far as i know, power all the wheels that touch the floor.

my 2 cents

Re: More Wheels?
 

you wouldnt be able to have that wheel be a break because you would have to change something in the wheel so that you make it a break. it is against the rules to alter the wheels in any way.

Re: More Wheels?
 

The Q & A system has clarified the use of a sensor to detect motion, and it doesn't have to be a KoP wheel. See This.

I plan on dragging a (computer) mouse.

Re: More Wheels?
 

No, you could just have it be rigid, or you could have the wheel turn in the oppisite direction. I don't see why you would need to alter the originality of the wheel.

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We added a 5th idler wheel today, but modified its position to not have any of the robot weight on it (ideally) to affect traction on the other 4 driven wheels. We started testing and should be able to report on our website in a few days.

Re: More Wheels?
 

Has anyone ever added a retractable wheel and gotten it to work? I'm not sure if thats what one of you were suggesting up top but we were thinking about trying to add a retractable wheel but we didnt know exactly how we should approach it...any ideas?

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http://cryptoniterobotics.org/images/2002.jpg

^ the 2002 robot, minus side panels and bumpers. And it was the most beastly robot FRC has seen. It pulled a small car (or so I've heard). Last that I have heard, it is still in (somewhat) working order.

For Andy's reminiscing pleasure: http://cryptoniterobotics.org/team/robots/

-Kat

Re: More Wheels?
 

i meant to get a closer look at SPAM's robot (180) at Florida but I believe they have, in addition to their normal drive and a fan, a set of wheels possitioned perpendicular to the others and they would pneumatically lower the wheels. these were mainly for a semi-swerve affect, but i suppose could be used as a break. I'm sorry i dont have a better explaination i only saw it from the stands.

Re: More Wheels?
 

Is it possible (and legal) that you make pneumatics strong enough that you mount a wheel perpendicular to other wheels, then when you want to brake, you gently lift the robot using that wheel, tilting it just ever so slightly, and applying that downward pressure and braking faster?

Imagine sliding your hand over the desk, and the sliding your hand over the desk with a lot of downwards pushing..?

Re: More Wheels?
 

You can only use up to 78 rover wheels in contact with the ground. No more.

Re: More Wheels?
 

If you think about it, that will only work as long as the robot mass is accelerating upwards.

As soon as the robot stops accelerating upwards (and begins to coast), the force pushing down on the wheels will return to its pre-acceleration value. But a robot cannot possibly keep moving upward forever, or even offset a partial amount of its downward acceleration due to gravity.

Therefore, the robot must begin to slow down its upward velocity, experiencing negative acceleration. During this period, the robot will actually have less normal force pushing down on the wheels, meaning less pushing power.

So yes, you can do this; you'd just get a very limited period of increased traction followed by a limited period of decreased traction.

Think of if like a roller coaster. When you go through a dip, you feel positive gee forces, and when you go over a peak you feel negative forces.

Re: More Wheels?
 

Thatz a bit harsh craig we wanted to use like 79.

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Doing some napkin calculations (read: no optimization), 112 is the hard limit for number of wheels you can have contacting the floor.

Re: More Wheels?
 

Our Software & Controls group has done very precise calculations and found that, at least for our machine, the limit is 112.67 wheels.

Re: More Wheels?
 

That's what you get for having your software guys do hardware calculations.;)

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Thanks for the trip down memory lane !
I'm glad to see 624 won the regional at Bayou !

Go CRyptonite !

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Wow ... Drill motors, No Kitbot Chassis, and the revolving light (How I loved that light).

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Here is a picture of our robot from that year for ya! We just call it the tank bot, and it just sits there doing nothing. And btw, that 5th wheel is the butt of many, many jokes lol. The 5th wheel is in the center of the robot, kind of hidden but nevertheless there.

http://picasaweb.google.com/RazorTip...3129 88959794

Re: More Wheels?
 

adding more wheels may increase your surface area, but it spreads out your weight. The net gain in traction: exactly 0. Even extra powered wheels dont help, assuming you keep the amount of power is the same. the only reason why 4 powered wheels could be better than two powered wheels is 1: more motors to power the 4 wheels, therefore more power or 2: if some of your wheels dont have traction, it's possible to pull yourself out of a bind with the wheels that do. It's a common misconception that more wheels = more traction, thats why you see so many 4 wheel drive cars in the ditch during wisconsin winters

Re: More Wheels?
 

Thanks, Michael. I only wish we had more than one picture of Tankbot from that year.

We have used it in demonstrations at least through 2007.

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LOL i did NOT see you had already posted a picture, sorry about that :ahh:

And I will work on getting more pictures of that robot for you, it is still lying around SOMEwhere...