Tank tracks vs. Wheels

[MBosompra]

My team (820) and I are considering using either Tank tracks or wheels. I have a few questions for those of you who know anything at all about tank tracks.

1) what are the pros and cons of tank tracks?
-we know that we'll gain torque
-we'll be able to make it up the step
-we think we won't loose much speed

2) Can we buy premade tank tracks? If so, from where and how much?

3) How do we make tank tracks?

4) How long does it take to build the tracks

5) Any words or advice or experieces would be greatly appreciated.

[Adam Shapiro]

Speaking from experience (we used treads in 2002):

Pros: One of the major pros of using treads is that you get a lot more traction on the bot. It will be much harder for other bots to push you around. Treads (with correct design) also make it easier for you to drive up the platform (from the 6" side panel).

Cons (Important!): Treads require a lot of torque as they produce a great deal of friction with the carpet. This is a major problem, especially if you aren't the greatest with a drive system and gearing (just like us in 2002), as turning becomes almost impossible and causes the breakers to blow quite frequently. Depending on where you buy them (we purchased ours from BrecoFlex) they may take quite a while to get to the school. Ours took over 4 weeks and left us with almost no practice time (under a day before shipping).

I'm not denouncing treads but I would be careful before using them.

[Paul H]

One thing you can do is mount a caster or two on pistons to deploy. This will almost emulate a 2 wheel drive and make it much easier to turn.

If you look at Truck Town Thunder's 2002 robot, it wobbled or hopped each time they turned it.

[Ryan Albright]

I am speaking from experience wiht treads to

we used treads in 2001 they do have great traction and all but they also add alot of weight. We did not like are experience wiht treads we debated using them this eyar but that was quickely turned down. I think its mostly a team preference i think if we used them again we might like them but just the experience with them and wheels we like wheels better but expermient see hwo you like them

[ggoldman]

You might want to look into one of the robots at the JPL (NASA jet propulsion laboratory) that can climb stairs and whatnot. IT uses tank treds with two extra "arms" to climb over terrain...

Happy hunting

G GOLDMAN

[Mike Norton]

Tank track are great.

We have had tracks for 10 years. So we know tracks and we know how far to push them.

1) Tracks are great to climb, push, pull, and to control.

2) Tracks are light if made right. they go a fast or as slow as you gear them.

if you look at theses pic's you can see how much power tracks can give you

http://www.valleytech.k12.ma.us/robo...ng%20Robot.jpg

http://www.valleytech.k12.ma.us/robo.../ClearRamp.JPG

Here is a close up of one of our track systems
http://www.valleytech.k12.ma.us/robo...02%20Track.jpg


Bad thing about tracks are if you go past there point of no return they rip

http://www.valleytech.k12.ma.us/robo...s/MVC-671S.JPG


these were Breco Flex timing belts. they have made better belts for us so they don't rip as easy. the cost is $270 per belt. the not so strong belts run around $140

If you want you can go back and look how our tracks have change in the past years

http://www.valleytech.k12.ma.us/robo...photos2002.htm


We left out 1999 becuase that year was a good year of climbing. you have to figure that one out on your own.

If you need anything esle just e-mail me

[Alexander McGee]

Originally Posted by Paul H

If you look at Truck Town Thunder's 2002 robot, it wobbled or hopped each time they turned it.

Only when our arms were up. If you lowered them, it wouldnt. LOL, it was funny to watch though.

[MBosompra]

Thanks to everyone for answering my questions. I have a few more for you guys.

1) How much roughly did it cost your team to build the whole tread system?

2) Did you have to have the inner wheel machined? Did you have anything machined?
3) How many of the belts did you guys rip?
4) How would my team go about making a tank tread?
5) I'm worried about turning with the treads, I think that it'll be a lot harder with treads and that we'll probably trigger the breakers.
6) Is it at all possible to buy a premade system and then just install it on our robot?

[Solace]

Originally Posted by MBosompra

Thanks to everyone for answering my questions. I have a few more for you guys.

1) How much roughly did it cost your team to build the whole tread system?

2) Did you have to have the inner wheel machined? Did you have anything machined?
3) How many of the belts did you guys rip?
4) How would my team go about making a tank tread?
5) I'm worried about turning with the treads, I think that it'll be a lot harder with treads and that we'll probably trigger the breakers.
6) Is it at all possible to buy a premade system and then just install it on our robot?

the easiest way to make turning easier on a tracked robot (or any robot for that matter) is to lower the center idler wheel down about 50 thousandths of an inch. This decreases your effective track length while turning, and still allows you to keep most of your traction.

a slightly more complicated, yet more effective solution is to have a mechanism that lifts one end of your robot off of the groung using skids or casters. when you get yourself into a situation when you need your traction again, you just plop the full length of your treads back onto the ground.

[Don Wright]

Here is something I found the other day when investigating drivetrain solutions. We still might use these, but maybe somebody else can as well.

It's pre-made, relatively cheap, can easily made lighter, and all you have to do is bolt some motors in to get it to work. Maybe it will work for you. I called them and they have a lot on stock (plus some other neat things on the site):

http://www.robotcombat.com/store_tanktreads.html

Only $140 + shipping for the set. They are only 20" long, but if you put them on the front of a bot with casters or the like on the back for stability (or even some kind of suspension), it could be a good combination.

Good luck.

[Adam Shapiro]

Originally Posted by 2000vfr800

...with casters or the like on the back.

Be very careful with casters! Even with treads you will lose a measure of control with your casters (although the surface area from the treads will most likely override this). We had that problem in 2001 (our rookie year) in which we used a combination of wheelchair wheels and casters; with that combination I believe our robot drove in a straight line only once or twice during the season...

[Don Wright]

Originally Posted by Adam Shapiro

Be very careful with casters! Even with treads you will lose a measure of control with your casters (although the surface area from the treads will most likely override this). We had that problem in 2001 (our rookie year) in which we used a combination of wheelchair wheels and casters; with that combination I believe our robot drove in a straight line only once or twice during the season...

Very good point...but hey...I'm an electircal enginer and my solution is, "We'll fix it with software!"

Honestly, it's a good point. Casters were just a quick suggestion.

[Adam Shapiro]

Originally Posted by 2000vfr800

"We'll fix it with software!"

I love it! I'm actually an EE/programmer by "trade" but I'm also co-captain of our team so one of my jobs is to know everything in a general sense as well as to know all of our past failures!

[KenWittlief]

castors work great if you close the steering control loop with a yaw rate sensor - then the SW can tell how much the driver wants to turn, and how fast the bot actually IS turning, and correct itself.

We did this last year - it works extreemly well!

[Tom Bottiglieri]

we have used treads for the past 3 years and have had nothing but luck with them.. they can climb pretty much anything if u design them right or have the proper lead in.. now about cost: my team put together a system last year that cost less than 400 dollars.. considering the amount of extra stability they give u, i would think its deffinitly worth it. i just cant imagine driving a bot that uses wheels and slides all over the place