We are making a robot that is about 3.5 ft. by 2 ft. wide. We are going to put some sort of tank tread on it but what we currently are using is not working. Currently our tread is two lines of chain that go around two sprockets each. They are connected with strips of Lexan that are riveted into the chain every fourth link. On the sprockets every fourth link is cut off so that the rivet pieces of Lexan line up with the cut out teeth on the sprocket. This system would work, but all of the holes on the Lexan pieces don’t line up, so the chain slips off often and then it simply doesn’t work. We are wondering if anyone has suggestions how to fix this, because if we can’t fix it we will have to come up with a new idea. We are thinking timing belts and pulleys, but we can’t find any that are wide enough. Does anyone have any suggestions on how wide the belt would have to be to be effective, and where we could find a fairly affordable belt that size?
This year our Breakaway robot used a tank tread drive system. In order to save money, we designed it to use triple-wide drive chain run on two sprockets, rather than buying belts from Brecoflex. I think the chain was available through some surplus store; I don’t know where we bought it. This worked out well for us since the chain was wide enough that we could use it as a track and it never slipped in competition. To make it legal, we attached small pieces of hose using bolts, as you can see in this picture.
Check out the local tractor supply store, you might find something that will suite your needs. In Oklahoma there was a team (i think it was 2824) that used some treads from a tractor supply equivalent and they never threw a belt and had crazy pushing ability. The treads I am thinking of were about 6 inches wide.
I am waiting for the pictures to be approved or whatever so I can give you the link on Chief Delphi. Also for the price question under a thousand is a must, and honestly under 500 would be ideal. The cheaper the better because we already have invested a decent amount of money into the system we have which is not really working, and we don’t have a large budget to work with.
I recommend buying a pulley/belt system from a company called “Polytech”, our team was EXTREMELY unsatisfied with our Brecoflex belts. Not only were they delivered way behind schedule, but also they snapped after only 3 or 4 matches, whereas the comparable polytech belts lasted an entire regional (12-14 matches) and an entire day of practice on our own field.
Thy consisted of aluminum C-stock fastened to chain that had special links that allowed things to be attached to them without modifying the sprockets. you can find them here: http://www.mcmaster.com/#roller-chain/=6s0umt Scroll down to the bottom and click on accessories. Unfortunately, they’re only available for 35 pitch chain.
I’ve never done this before, but I would suggest timing belt since it requires fewer modifications than chain, and has fewer moving parts and joints. also, I would check to make sure the chain/belt is tensioned properly and hasn’t stretched.
The simple and cheap solution may be to go with a higher pitch chain. I would think #35 at the smallest, but even higher may be necessary so the teeth of the sprockets have more chain to dig into as the whole assembly rotates.
I’d also recommend you fix the “holes don’t line up” issue. It sounds like you have many lexan pieces and they all need to be identical. A jig, automated process, or assembly line may be in order. Look for defects as they come out of cutting/drilling and discard any grossly imperfect pieces.
We actually looked at those and our considering getting them. This is what we currently have.
http://www.chiefdelphi.com/media/photos/35658
This is our drive system with shocks…we still need a dynamic tensioner so currently we are just trying to get it working with the shocks locked and static. http://www.chiefdelphi.com/media/photos/35656
This is the tread but we will be putting something over the lexan pieces so they grip the ground better. http://www.chiefdelphi.com/media/photos/35657
This is a close up of the sprocket. If you look to the right of the sprocket you can see where we cut off the teeth so we could rivet the lexan pieces to the chain.
We used tank treads exclusively in the mid-late 90s. Given, this was for carpet with FRC, but your pushing ability is absolutely unmatched, but your speed tends to be slower, and your maneuverability is arc and circle limited.
We used something similar to the brecoflex treads with very high levels of success. We never slipped a tread after our ~first year using them. You need to be very careful how you design your tensioner and idler and where you place your bogies.
Team 578 this year, my team, was considering the same thing when we found triple starnd chain. its the same Idea but you bolt the lexan to the outer stands and run a regular sprocket on the inner strand. it will work exactly as you want it to. it can be bought from any specialty chain store online. alas it is expensive.http://www.lucasindustrial.com/images/line/ch_rc_r3.gif
Might be above your cost range, but we’ve been very happy with the Outback track systems. Effectively it’s a Brecoflex self centering belt riding on pulleys between milled aluminum, but it could probably be simplified down to a brecoflex belt on pulleys with some cheaper structure. If you’re interested, Outback MFG is a Brecoflex reseller, so you can get some FIRST legal belts through them. (You’ll need to contact them for details… I’m not current on what belts they carry in stock, or costs, or even availability…)
If we had more information about your application, I’m sure we could help you out with more accurate information…
The outback systems from what I heard didn’t work out well. I only saw 2-3 Robots at Worlds with Treads, the both had belt treads. http://maikenmagic.com/?ref=showphoto&dir=2010%20FRC%20Build&num=8
We handmade our using Kevlar belting, ABS plastic, and Rivets…lots of rivets.
