Traction is Key!!!!
 

Posted by Elgin C at 03/20/2001 1:09 PM EST


Engineer on team #237, Sie-H20-Bots, from Watertown High School / NVCC.



As the title states I believe that traction is key if you have any chance at winning. Our first robot that we built had the stock straight out of the box 6" wheelchair wheels on them. We had very little traction going up the ramp and so we made our ramp extender feature of the robot act as a counter balance to make it up the incline. But that didn't work because we ended up tipping ourselves over a few times. Fortuanately we righted our selves in enough time to get into the endzone but lost major points for our alliance.

Our remedy: All four wheels were burned with a woodburner with a space in between all of the burns. If you do this make sure you do it in a well ventilated area though!!! The wheels give off alot of smoke when being burned.

Re: Traction is Key!!!!
 

Posted by Deej- T190 at 03/20/2001 3:01 PM EST


Engineer on team #190, Gompeii, from Mass Academy and WPI.


In Reply to: Traction is Key!!!!
Posted by Elgin C on 03/20/2001 1:09 PM EST:



: As the title states I believe that traction is key if you have any chance at winning. Our first robot that we built had the stock straight out of the box 6" wheelchair wheels on them. We had very little traction going up the ramp and so we made our ramp extender feature of the robot act as a counter balance to make it up the incline. But that didn't work because we ended up tipping ourselves over a few times. Fortuanately we righted our selves in enough time to get into the endzone but lost major points for our alliance.

: Our remedy: All four wheels were burned with a woodburner with a space in between all of the burns. If you do this make sure you do it in a well ventilated area though!!! The wheels give off alot of smoke when being burned.


another way of making the treads is to use a vertical mill and make the grooves like that (if you have the time). Thats what we did here on T190, and no problems with traction at all....

Re: Traction is Key!!!!
 

Posted by Andrew wyatt at 03/21/2001 1:02 AM EST


Other on team #524, Alpha Omega Robotics, from South High School.


In Reply to: Re: Traction is Key!!!!
Posted by Deej- T190 on 03/20/2001 3:01 PM EST:



: : As the title states I believe that traction is key if you have any chance at winning. Our first robot that we built had the stock straight out of the box 6" wheelchair wheels on them. We had very little traction going up the ramp and so we made our ramp extender feature of the robot act as a counter balance to make it up the incline. But that didn't work because we ended up tipping ourselves over a few times. Fortuanately we righted our selves in enough time to get into the endzone but lost major points for our alliance.

: : Our remedy: All four wheels were burned with a woodburner with a space in between all of the burns. If you do this make sure you do it in a well ventilated area though!!! The wheels give off alot of smoke when being burned.

:
: another way of making the treads is to use a vertical mill and make the grooves like that (if you have the time). Thats what we did here on T190, and no problems with traction at all....

Thats what we did here at team 524, also. we managed to get too much traction from our wheels, making the breakers trip every time we take a turn too tight.

Re: Traction is Key!!!!
 

Posted by Jeff Waegelin at 03/24/2001 8:36 PM EST


Student on team #201, Visteon FEDS, from Rochester High School and Visteon Automotive Systems.


In Reply to: Re: Traction is Key!!!!
Posted by Deej- T190 on 03/20/2001 3:01 PM EST:



That was a creative idea, but my team tried a very similar process on our wheels with no success. We had a traction problem throughout the West Michigan regional. Grooves in the wheels were not enough, so we ordered some treads made from timing belt to attach to our wheels. This solved our problem.

Jeff

:
: another way of making the treads is to use a vertical mill and make the grooves like that (if you have the time). Thats what we did here on T190, and no problems with traction at all....

wheelchair wheel just aren't going to cut it
 

Posted by Ken Leung at 03/20/2001 3:10 PM EST


Student on team #192, Gunn Robotics Team, from Henry M. Gunn Senior High School.


In Reply to: Traction is Key!!!!
Posted by Elgin C on 03/20/2001 1:09 PM EST:



Good call about the traction...

Usually when people are thinking about a drive train, they usually only think about how much gear ratio the motors have, or how much speed/torque do the motors transfer onto the wheels.

However, that's only part of the problem. The over all goal of a drive train is to transfer one form of energy into another, and one form of an motion to another. Although motors take care of turning electrical energy into mechanical energy, you still have to think about how to transfer that rotational mechanical energy into linear motion.

The most common way of solving that problem is using wheels or thread. But you have to understand that those things work because of a major thing: Friction.

And from that standpoint, you have to start worry about how to get maximum friction allowed on the wheels/threads in order to get most from the rotational energy. Then you have analyze how the wheels/threads react under different kind of stress: the weight of the robot pushing onto the wheels, the carpet pushing against the wheels with the same amount of force the wheels are pushing against the carpet, side friction when spinning in circle... etc.

Finally you have to look and see if the material on the wheels are capable of taking so many stress, then think about the trade off between the life-time of the wheels, the energy you are losing, the cost of manufacturing, and the need for the competition...

After all these work, you should be able to conclude that normal wheelchair wheels are just not going to cut it, that is without any improvements anyway... But of course most people just need to try them out and immediately see the lack of traction.

Ha. Who need all the analysis when you can just test the stuff out?

Re: wheelchair wheel just aren't going to cut it
 

Posted by Deej- T190 at 03/20/2001 3:47 PM EST


Engineer on team #190, Gompeii, from Mass Academy and WPI.


In Reply to: wheelchair wheel just aren't going to cut it
Posted by Ken Leung on 03/20/2001 3:10 PM EST:



thats when your team develops "wonderwheels", like ours did. not only do they reduce drag when turning which loads up motors, the also effectively move your pivot point to the opposite end of the bot, making manuevers around balls for pick up much quicker. they also improve all around traction on the carpet as they actually are grooved to close to the same pitch as the carpet used on the field. You can take a look at various pics posted on the web of these "wonderwheels" or take a look at them in the pits at nationals.....see you there

Re: wheelchair wheel just aren't going to cut it
 

Posted by Patrick Dingle at 03/21/2001 10:25 PM EST


Coach on team #639, Red B^2, from Ithaca High School and Cornell University.


In Reply to: wheelchair wheel just aren't going to cut it
Posted by Ken Leung on 03/20/2001 3:10 PM EST:



I agree with you completely... but have a couple comments to add. Torque is important, but torque doesn't mean anything if your robot can't grip the carpet! What we're dealing with here is static friction. Static friction tells you the maximum amount of sideways (perpendicular) the wheels of your robot can exert on the field before they slip. This maximum force is equal to the coefficient of friction multiplied by the "normal force" (the force of the robot on the ground). So there are two ways to increase the maximum amount of force your robot can exert without slipping:
1) a heavier robot
2) increasing coefficient of friction

There are many ways to increase the coefficient of friction... grooves, "wonder wheels", etc... However, there is a maximum grip that you can possibly get on carpet, and you can't do much better than grooved wheels. Therefore, if you've already grooved the wheels and stuff, and still have trouble, then you most likely have a light robot, and you can't do too much better with increasing coefficient of friction... unless you go to treads.

Another point: power all wheels. Unpowered wheels is just a waste of traction & torque.

Anyway, enough physics from me!

Patrick

: Good call about the traction...

: Usually when people are thinking about a drive train, they usually only think about how much gear ratio the motors have, or how much speed/torque do the motors transfer onto the wheels.

: However, that's only part of the problem. The over all goal of a drive train is to transfer one form of energy into another, and one form of an motion to another. Although motors take care of turning electrical energy into mechanical energy, you stil

Re: wheelchair wheel just aren't going to cut it
 

Posted by Patrick Dingle at 03/21/2001 10:27 PM EST


Coach on team #639, Red B^2, from Ithaca High School and Cornell University.


In Reply to: wheelchair wheel just aren't going to cut it
Posted by Ken Leung on 03/20/2001 3:10 PM EST:



I agree with you completely... but have a couple comments to add. Torque is important, but torque doesn't mean anything if your robot can't grip the carpet! What we're dealing with here is static friction. Static friction tells you the maximum amount of sideways (perpendicular) the wheels of your robot can exert on the field before they slip. This maximum force is equal to the coefficient of friction multiplied by the "normal force" (the force of the robot on the ground). So there are two ways to increase the maximum amount of force your robot can exert without slipping:
1) a heavier robot
2) increasing coefficient of friction

There are many ways to increase the coefficient of friction... grooves, "wonder wheels", etc... However, there is a maximum grip that you can possibly get on carpet, and you can't do much better than grooved wheels. Therefore, if you've already grooved the wheels and stuff, and still have trouble, then you most likely have a light robot, and you can't do too much better with increasing coefficient of friction... unless you go to treads.

Another point: power all wheels. Unpowered wheels is just a waste of traction & torque.

Anyway, enough physics from me!

Patrick

: Good call about the traction...

: Usually when people are thinking about a drive train, they usually only think about how much gear ratio the motors have, or how much speed/torque do the motors transfer onto the wheels.

: However, that's only part of the problem. The over all goal of a drive train is to transfer one form of energy into another, and one form of an motion to another. Although motors take care of turning electrical energy into mechanical energy, you still have to think about how to transfer that rotational mechanical energy into linear motion.

: The most common way of solving that problem is using wheels or thread. But you have to understand that those things work because of a major thing: Friction.

: And from that standpoint, you have to start worry about how to get maximum friction allowed on the wheels/threads in order to get most from the rotational energy. Then you have analyze how the wheels/threads react under different kind of stress: the weight of the robot pushing onto the wheels, the carpet pushing against the wheels with the same amount of force the wheels are pushing against the carpet, side friction when spinning in circle... etc.

: Finally you have to look and see if the material on the wheels are capable of taking so many stress, then think about the trade off between the life-time of the wheels, the energy you are losing, the cost of manufacturing, and the need for the competition...

: After all these work, you should be able to conclude that normal wheelchair wheels are just not going to cut it, that is without any improvements anyway... But of course most people just need to try them out and immediately see the lack of traction.

: Ha. Who need all the analysis when you can just test the stuff out?

Wheelchair Wheels Don't Cut It? That's Not Always Bad.
 

Posted by Dodd Stacy at 03/22/2001 5:23 PM EST


Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.


In Reply to: wheelchair wheel just aren't going to cut it
Posted by Ken Leung on 03/20/2001 3:10 PM EST:



We all do our best to design bots to play the game, and that always means attending to traction. We've had a lot of discussion, learning, and teaching on these boards about friction coefficients, normal forces, and surface shear.

But these robots do other things after the season, and some of those things have as much to do with FIRST's goals and its future as does playing the competition matches well. I'm specifically talking about the team students touring the bot around to local Elementary and Middle schools and putting on demos for the younger kids. Talk about a hit, and a heck of a recruiting tool.

These demos almost always happen in the school's gym, which almost always has a hardwood (basketball court) floor. Usually someone in the school is mighty particular about damaging or even marking that floor. So think about how you can design a competitive bot which makes its traction in a way that still lets it run on a court without damage, or about an alternate set of "demo wheels" for that purpose. Believe me the 6th grader taking a turn at the stick won't care if she can't shred 4x6's and get air.

Dodd

DOnt even use the rubber wheels
 

Posted by Gabe at 03/20/2001 8:23 PM EST


Student on team #384, Tucker TIgers, from JR TUCKER HIGH and Infineon/Invensys/SHowbest Fixtures/ Nasa Langley .


In Reply to: Traction is Key!!!!
Posted by Elgin C on 03/20/2001 1:09 PM EST:



My team .. 384 manufactured our own wheels on a CNC lathe. I designed them and then we took it to one of our sponsers to get it made from wood. We made about 3 sets. Each wheel got some timing belts apoxyed to em to make em get the traction they need.

Also.. we have an optional 5th wheel that can come down when needed so that we can get high torque for towing.. pushing.. or balancing.. COOL HUH?
That 5th wheel was one of the reasons why our team was awarded the leadership in control award at our regional (2nd year in a row we won it)

Later..

Gabe GOldman
Head of design team on team 384
GO SPARKY

Re: Traction is Key!!!!
 

Posted by Jason Flanagan at 03/20/2001 11:31 PM EST


Student on team #250, Dynamos, from Shenendehowa HSE and General Electric, Verizon, .


In Reply to: Traction is Key!!!!
Posted by Elgin C on 03/20/2001 1:09 PM EST:



Yeah looking at traction our team well, my dad (thanks dad!) designed a kick $@#$@#$@# track system driven by a center wheel for stability. Even with the track system you still need one more thing to make any system work Friction. To get friction you need weight on top of your robot to weigh down the tracks/wheels so they have more traction. This was actually the first year in a few years that our team was UNDER the weight limit. Our 10 year teacher, Paul Kane was actually pissed that we were about 30 lbs under the limit. But we added some weight, added aluminum instead of lexan, lbs here and there, and eventually made it up closer to the limit. So if there are robots out there who are 100 lb weaklings bulk up! add some weight to your robot, make it closer to 130 and that should gain you some traction so you can make it over the bridge easier.