My team is making a basic 6 wheel drive base with the IFI KITBOT, and we are interested in using timing belts instead of chain. We’re planning to have the SuperShifter transmissions between the front and middle (lowered 1/8") wheel, with 2 belts on each side, one connecting transmission/front-wheel/mid-wheel and another connecting mid-wheel/back-wheel.
We’re using 6 grey Andymark wheels from the KoP and 3/8" d steel axles. This robot is meant to be a durable and fast (~11 fps) base for drivers to practice with.
What belts and pulleys we should use (manufacturer, width, part #, etc.)?
Do we need to buy the exact length, or is there a way to cut and re-attach (could we use the 10’ Gates belting from the kit)?
Do we need a way to tension, or will there really be no stretching?
Any suggestions?
We have used 6 wheel drive for many years, but #25 chain for the drive. We have considered using belts, but have felt that belts take a little more width away from the robot footprint, where space has been at a premium. Belt tension is extremely important with belts, so put a tensioning adjustment into your design for every belt. I would also suggest using a COTS belt rather than try to put a custom length onto your machine.
We have also used the drive configuration you are considering, but would suggest runnng the wheel to wheel belt from the mid wheel to the front, rather than the rear. When you get into a pushing match, the front wheels will not provide any traction as they will lift. I would also suggest you consider a drive belt to each wheel, so you can still drive, even if several belts break. Design so belts can be changed easily, and keep spares on hand. I haven’t looked at the load capabilities of belts, but #25 chain can take 750 lbs of load. The only time we have broken a chain is whe another robot part got in betwen our sprocket and chain, deleoping tremendous load, and we were still able to compete. PM me if you need any other info.
Might i advise that you/your team not make any major purchases/decisions before the game is announced…Bill and Dave have strongly advised that teams don’t make major plans…:D.
We used belts on one of our robots a couple of year ago. We found that if you dont tension the belts then they will skip. It doesnt seem to hurt performance, but it can scare people with how loud the skipping is.
If your belts are slipping, it has to hurt your performance-it means you’re losing tons of efficiency.
I believe 125 used belts either last season or in 2007, and they did not like them at all. If I remember correctly they ended up swapping them for chains. Do a search and you can find the thread about them.
Just stick with chain… it works. I’ve seen a couple teams try timing belts, and I haven’t heard anything positive yet. Timing belts are very tough to do in high load situations, chains are designed for higher loads. Why change what’s proven to work?
V-belts require very high tension to work which equals high friction and inefficiency. Timing belt is a much better option in every factor except perhaps cost although it is definitely worth it to not use v belt
There was one team that tried v belts I believe in 2007 and the belts failed miserably. A couple teams have used timing belts successfully such as team 125 and team 118 uses them to some extent. You just have to design for them instead of using them the exact same as chain. For instance, you need to have a lot of wrap around the pulleys and the belt must be tensioned properly, although once tensioned the belt stretches much less than chain.
Cory,
We did use belts this season (2008), but ended up having a lot of success with them. We used 25 chain in 2007.
As for the original topic,
I have posted on a few threads already (a quick search should churn them up). Belts are definitely something teams can do, but as stated above, tension is key with them. We used kevlar reinforced belts which basically eliminated “stretching” so we did not need an active way of adjusting the tension. I would suggest doing a lot of research to make sure they are something you want to consider.
Right now I could not tell you what our plan is for the upcoming season. We are proud we used belts effectively and we will see what the game is before we commit to using them again.
The statement that belts cannot handle high torque is false. Lots of machines like large mills and motorcycles use belts without any trouble.
The problem with belts is that they are not good at changing directions quickly. Often, when they go from forwards to reverse very quickly, (as in a FIRST robot) they skip teeth or go flying off.
Notice how 118 only needs to drive their wheels 1 direction?
We ordered our belts from http://www.sdp-si.com/. They are a reliable source, equivalent to any kind of supplier. They offer a large variety of sizes, lengths, and materials in both the pulley and the actual belt.
Properly installed chain is definitely more efficient then timing belt (or any other drive system). That’s why bicycles have gone back to chain time and again. Should be less expensive also. You don’t have to order the right length. You don’t have to compromise your design to fit an available belt length. Splicing a continuous loop belt is not easy to do well and lowers the strength, torque rating, and durability. You can break chain to remove/install with other drive elements still in place. Timing belts have advantages for noise, accuracy, longevity, low maintenance, set and forget, as well as a back surface that can transport objects.
V belt is less efficient than timing belts.
Steve des Jardins
Mentor Team #2102
