Tank tracks vs. Wheels
 

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.

Re: Tank tracks vs. Wheels
 

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.

Re: Tank tracks vs. Wheels
 

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.

Re: Tank tracks vs. Wheels
 

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

Re: Tank tracks vs. Wheels
 

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

Re: Tank tracks vs. Wheels
 

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

Re: Tank tracks vs. Wheels
 

Your assumption that treads will give you more torque is not true. You will have the exact same amount of torque as if you used wheels.

Cons: One glaring con nobody mentioned is that you have to tension them properly. If you dont, theyll fall off when you try to turn.

Perhaps the biggest con is their steep price tag. Belts are around $270 each as someone said, plus you need the pulleys, which will run you another couple hundred. All said, youre going to spend near 1000 dollars, just to get the robot running. Also, I believe many teams who used treads either tore them like crazy, or wore them down very fast. I seem to remember 226 saying they used 7+ belts over the course of the season. That adds up to quite a bit of money.

Re: Tank tracks vs. Wheels
 

Ahh yes the age old tread vs. wheel debate. All of us (by all i mean some) from team 862 have tried to stay away from this but every year it comes back. I say wheels because its easyer, but its your choice.

Re: Tank tracks vs. Wheels
 

You are right Cory, we spent a literal fortune on the tracks last year and it would make me think twice about doing it again (Can't remember if it was seven or eight ripped belts). As Cory stated above the self aligning pulley's were $100 each ($400 total) and the belts were close to $150 for serrated and almost $300 for the solid center. As for shipping them, Brecoflex ran pretty far behind in getting us replacements, and our use for them is way out of their design parameters as far as Brecoflex was concerned. Our gearboxes may have been too much for them last year. Also, don't think that because you have treads you can climb anything, it all depends on the type of treads and their orientation compared to the chassis (Look at most tanks and the front has a steep angle instead of a big pulley)

I haven't checked with the company that Andy Baker posted but they may be better price or delivery than Brecoflex and they sell self aligning tracks there also.

On a side note, we noticed no difference in the tearing between the regular Brecoflex belts with the serrated center rib and the solid core which cost twice as much. Our failures started on the edge of the tread and continued across the belt and appeared to have nothing to do with the center. Many teams also had de-lamination problems with the tracks.

Treads are definately cool, they suck power out of the drivetrain like no other on turning, and you can get great traction, but, don't sell pneumatic tires short. I was VERY impressed with the performance of some of the six wheeled bots out there and their pushing force

Re: Tank tracks vs. Wheels
 

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

Re: Tank tracks vs. Wheels
 

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?

Re: Tank tracks vs. Wheels
 

Our team (1177) went through this analysis and decision making process today. We eventually created a decision matrix listing our options which ranged from 2 wheeled, 2 motor drive up to multi-wheel/tread and multi-motor drive. We ended up deciding to use wheels and multiple motors in a 4 wheel drive configuration for a combination of reasons.

The main reason is as stated in the replies thus far. Treads are great for traction, however that traction comes at a price which is increased power draw. Along with that power hungry traction system, your speed/current ratio is lower. We resisted the urge this year to use treads, and will utilize the 4 wheel drive.

Re: Tank tracks vs. Wheels
 

When you guys ripped your tread, how tight were the belts?

We used an alligator clip in 2001 which in my opinion is significantly weaker then a solid belt and those did not break, Im really at a loss for why your belts would snap like that?

Re: Tank tracks vs. Wheels
 

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.

Re: Tank tracks vs. Wheels
 

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.

Re: Tank tracks vs. Wheels
 

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...

Re: Tank tracks vs. Wheels
 

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.

Re: Tank tracks vs. Wheels
 

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!

Re: Tank tracks vs. Wheels
 

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!

See...fixing it with software!!! :p

Good suggestion.

Re: Tank tracks vs. Wheels
 

I've seen a lot of team have those similar problems with Brecoflex belts.

You can get belts with the same backing from Mectrol (www.mectrol.com). The lead time is roughly the same. We've never lost a belt, and we've loaded them as much as anyone. The belts we used were kevlar reinforced, which is probably why we haven't lost one. I believe the Brecoflex belts are not reinforced, but I don't know that for sure.

Re: Tank tracks vs. Wheels
 

Our tracks were actually quite tight, as requested by Brecoflex to make them ride in the pulleys correctly. When we first switched to the solid core tracks they didn't ride in the pulleys well, this matched up to what Mike Norton on 61 also saw and Brecoflex told us to tension a bit more. We ended up machining the center groove to be slightly wider and they ran fine. As for why they broke, who knows but last year our robot was output serious power with the shifter and in low it could spin the tracks against an immovable object.

On a side note, it is hard to tell but our center idler wheels are down a fraction of an inch to help turn.

Re: Tank tracks vs. Wheels
 

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

Re: Tank tracks vs. Wheels
 

Our team has used treads and wheels in the past. Unfortunately i was not on it when we had treads, although i have driven one of ours with treads and it drives great. There is one main thing i think of when i think of treads and that is a whole lot of friction which can either work for or against you. Traction is good to have when pushing or climbing, but if you have too much then your robot wont be able to overcome it to make a turn. So when designing you need to come up with good ways to do that. Last year our robot had 6 wheels and the center 2 were lower than the other 4. Being able to do something like that in the center of the treads would be pretty neat. We took our center wheels off after the Buckeye Regional because if anyone recalls our robot's performance you would realize that it spent more time on its back than its wheels. So you will have to rember that it will make you tipsy and you may want to design something to keep you on your treads or you will do really bad. We took the middle wheels off and added a pneumatic cylinder on the back that we put out before going up the ramp and we kept on our wheels pretty good. This Year is looking like treads for us so i will get to experience the "horror" of assembling and putting them on. Lol. This year is going to be another fun year of trial and error.

Re: Tank tracks vs. Wheels
 

Ok, first off, you could make it up the stairs with wheels too, depends on the wheel diameter, and tracks do require more torque because as stated in someone’s reply, more friction, with that comes more traction, a big pro for tracks when you need that kind of bite. You need a beefy drive system to handle the forces, as someone stated the added power needed to move your robot will increase your current draw, and if it isn't designed right, you could be blowing your breaker or fuses every time you tried to turn. In the past we have used the 3/16 drill motors with variable speed gear boxes which worked just fine, and now with the 1/2 inch drill motors, power and robustness of the motors is less of a worry as they are strong and built very well, like we would expect any less from Bosch. As for the tank tracks you could use a double sided timing belt, many teams have used that in the past, with good results. If you were to make a track system like the one on a real tank, you would need to make each individual pad and then link them together, the system is complicated, and would weigh a lot. If you ever get the chance to check out a tank up close and personal you will see that the system has many pads connected together, then driven by a large drive sprocket. If you do go tracks, you will need to insure the tracks tension is maintained so that the track won’t slip, one possible way to do it is to use some type of variable pressure tensioning device so that you can calibrate and fine tune the tension applied. So, wheels or tracks, it really depends on your strategy, do you want to get up the stairs, do you want to try and climb the side? Do you want to be very fast, and nimble? As for the time it takes, a well thought out drive system will take some time, both wheel and track systems will take a few weeks to fully think out and build. The great tracks vs. wheels debate will continue every year, and it depends on what you think your robot needs to do, and besides, who said it needs to be one or the other, there are other options out there to explore and come up with, don't limit yourself.

Re: Tank tracks vs. Wheels
 

This year our team figured a way around the friction problem, while still being able to have the tracks all the way down for pushing and pulling matched whenever we want. :D

-Aaron

Re: Tank tracks vs. Wheels
 

Did you solve the problem for the upcoming competition or did you solve it for the 2003 comp? Care to share your secrets?

Re: Tank tracks vs. Wheels
 

Drop the center roller 1/4"-1/2" You'll pivot on it while turning.

Cory

Re: Tank tracks vs. Wheels
 

This upcoming season. it's a system that allows us to have Full treads on the ground for pulling, then quickly i.e. 2-3 seconds switch to only having four points of contact with the ground measuring roughly 1 inch by 2 inches so we will be able to turn quickly, without blowing breakers. If you want more info PM me or hit me up on AIM.

-Aaron

Good Luck to All!