Tank tracks vs. Wheels

[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!

[Don Wright]

See...fixing it with software!!!

Good suggestion.

[Chris Hibner]

Originally Posted by Matt Reiland

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.

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.

[Matt Reiland]

Originally Posted by Jim Giacchi

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?

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.

[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

[Scott team 48]

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.

[coreyjon]

Originally Posted by 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.

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.

[Aaron Lussier]

Originally Posted by Adam Shapiro

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.

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.

-Aaron

[Adam Shapiro]

Originally Posted by Aaron Lussier

This year our team figured a way around the friction problem

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

[Cory]

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

Cory

[Aaron Lussier]

Originally Posted by Adam Shapiro

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

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!