do tracks and wheels together make a better robot?

[gondorf]

is it true that having both tracks and wheels together make you more likely to be picked for the better teams. i just heard that they might be better for traction.

which brings up another rumor: do tracks increase ball accuracy?

[KenWittlief]

Tank tracks are one of those things that keep showing up on FIRST robots, in ways that I dont understand.

Friction requires a downward force. If you look at an army tank, or a bulldozer, there are idler wheels all down the side that push the track into the ground.

but I have never seen a FIRST robot with those idler wheels. If you dont have them, then what is pushing the tread into the carpet between the wheels?

ans: nothing!

I might be wrong on this, but a robot that has two wheels on each side with a tank tread, and a robot that has two wheels on each side that use the tank tread wrapped around the wheels instead (as tire material) should have exactly the same pushing force

and way less complexity

[Ken dons his fire retardant suit and hides under desk]

[sburro]

Originally Posted by KenWittlief

Tank tracks are one of those things that keep showing up on FIRST robots, in ways that I dont understand.

Friction requires a downward force. If you look at an army tank, or a bulldozer, there are idler wheels all down the side that push the track into the ground.

but I have never seen a FIRST robot with those idler wheels. If you dont have them, then what is pushing the tread into the carpet between the wheels?

ans: nothing!

I might be wrong on this, but a robot that has two wheels on each side with a tank tread, and a robot that has two wheels on each side that use the tank tread wrapped around the wheels instead (as tire material) should have exactly the same pushing force

and way less complexity

[Ken dons his fire retardant suit and hides under desk]

lokk at 663 robot last year
http://www.wcsrobotics.com/multi.htm

The idlers on the bottom could have been spring loaded but since it was a flat field there was no reason to.

[KenWittlief]

wow! hats off to you!

I think that is the 1st time Ive tank treads done 'right' on a FIRST robot

is your team sponsored by General Dynamics by any chance?

or Catapiller? :^)

regarding launcher accuracy - if a robot is able to turn slowly and precisely, then it is easier to target the goal

since tank treads have a lot of side friciton, they are usually geared down more than a robot with two wheels and castors (for example) - so a typical bot with treads will turn slower

and be easier to aim.

[henryBsick]

Originally Posted by KenWittlief

Tank tracks are one of those things that keep showing up on FIRST robots, in ways that I dont understand.

Friction requires a downward force. If you look at an army tank, or a bulldozer, there are idler wheels all down the side that push the track into the ground.

but I have never seen a FIRST robot with those idler wheels. If you dont have them, then what is pushing the tread into the carpet between the wheels?

ans: nothing!

I might be wrong on this, but a robot that has two wheels on each side with a tank tread, and a robot that has two wheels on each side that use the tank tread wrapped around the wheels instead (as tire material) should have exactly the same pushing force

and way less complexity

[Ken dons his fire retardant suit and hides under desk]

Ken,
I would like to thank you for finally bringing this into the light. I am pretty frustrated with teams that design drive-trains based on poor physics beliefs. From treads to unnecessary three motor drive trains...
Anyway, knowing vectors of force and co-efficients of friction are HUGE keys to building a competitive robot.

-Henry

[George1902]

Originally Posted by KenWittlief

but I have never seen a FIRST robot with those idler wheels.

You should swing by the Florida Regional this year, Ken. I know of one team there who does treads quite well.

http://www.spamrobotics.com/gallery2/build05/robot05
http://www.spamrobotics.com/gallery2.../2003_on_field
http://www.spamrobotics.com/gallery2/2002/pk02pits
http://www.spamrobotics.com/gallery2/2001/3_bits

[RogerR]

Originally Posted by Henry_222

Ken,
I would like to thank you for finally bringing this into the light. I am pretty frustrated with teams that design drive-trains based on poor physics beliefs. From treads to unnecessary three motor drive trains...
Anyway, knowing vectors of force and co-efficients of friction are HUGE keys to building a competitive robot.

-Henry

i'm curious about what you mean by 'poor physics beliefs'. both of those examples have valid reasoning behind them. and i'm pretty confident that their designers have at least a rudimentary grasp of Co.F. and vectors.

[KenWittlief]

we were talking about tank treads that do not have idler wheels. The photos posted in this thread are the 1st bots Ive seen that do have idler wheels (the right way to use threads)

un-necessary 3 motor designs are designs that dont need 3 motors on each side -it depends on what else the drive train can do. If a bot can spin its wheels against a wall, then putting more motors on it does nothing but spin the wheels faster

and spinning the wheels faster does not give you any additional pushing force.

[Ken hides back under his desk :^) ]

[Sean Schuff]

To accomplish a downward force on the track between the rear/front drive/idler does not require idler wheels. A rail (similar to older snowmobile designs prior to popular use of bogey wheels) will accomplish the same thing. It has to be designed right so as to not cause unnecessarily high amounts of friction. Without running numbers my hunch is that the bogey wheels are more efficient in the area of reducing friction.

With regards to the logic of using treads versus wheels - I think this year's game is a perfect example of the usefullness of tracks. Why? If your team wants to climb the ramp to score the points at the end of the match you need either ground clearance to the tune of roughly 4.5 inches on a 38" long drive with 6 inch wheels. This approach causes two problems that our team has identified - less space in the 28x38x60 box for robot "stuff" and a higher center of gravity. Tracks eliminate the need for ground clearance by providing contact all along the robot.

With that being said, our team is still using wheels this year but in a slightly different configuration than years past. Our team has not put much effort into tracks and if I keep mentioning them, Mike Johnson will kick me again!

My 2 cents - take them for what they're worth.

Sean

[Jonathan Norris]

Originally Posted by Sean Schuff

With regards to the logic of using treads versus wheels - I think this year's game is a perfect example of the usefullness of tracks. Why? If your team wants to climb the ramp to score the points at the end of the match you need either ground clearance to the tune of roughly 4.5 inches on a 38" long drive with 6 inch wheels. This approach causes two problems that our team has identified - less space in the 28x38x60 box for robot "stuff" and a higher center of gravity. Tracks eliminate the need for ground clearance by providing contact all along the robot.

Sean

My team did a test today with a extra kit frame with 6" 6 wheel drive, and only needed 2.5" of clearance. This is with 6 wheels not 4.

[Sean Schuff]

Originally Posted by Jonathan Norris

My team did a test today with a extra kit frame with 6" 6 wheel drive, and only needed 2.5" of clearance. This is with 6 wheels not 4.

We ran the same caculations and came up with the same number. We are also looking at a 6 wheel configuration with the front and rear wheels driven and the middle wheels serving simply as bogeys. It definitely gives you more options with internal configurations.

[sanddrag]

If you do it correctly, you can get away with as little as 2mm clearance for 6wd. Of course that doesn't allow for wheel wear or running over dropped bolts or anything.

[Sean Schuff]

Originally Posted by sanddrag

If you do it correctly, you can get away with as little as 2mm clearance for 6wd. Of course that doesn't allow for wheel wear or running over dropped bolts or anything.

Yes but can you climb the ramp AND get onto the platform that way? My guess is "no". You can get up onto the ramp with minimal clearance simply by placing the contact point between your front/rear wheels and the floor beyond the exterior of your frame. This will get you on the ramp but you will high side your robot trying to get to the top of the platform. There are two options to solve this dilemma: a) tracks or wheels all along the lower drive section of your robot or b) an area between the wheels that allows for the transition from the ramp to the platform.

[Tom Bottiglieri]

Originally Posted by KenWittlief

T

but I have never seen a FIRST robot with those idler wheels. If you dont have them, then what is pushing the tread into the carpet between the wheels?

You sure?

All of the benefits of tank treads. All of the benefits of 6WD. Very little hassle.

[Nuttyman54]

Team 971 took a slighty different approach in 2004. We did a halftrack (Tracks in front, wheels in back) and use the Robot Combat snowblower treads. however, we also inclined the treads quite a bit, giving the robot effectively a 6 wheel configuration. This allowed us to drive up the SIDE of the platform (We skipped the 6" steps entirely)...it also helped us get top seed and win the Silicon Valley Regional that year (thanks to 254 and 852). You could use the same concept to drive up the ramp.