Re: Timing Belt Drive System
 

The only time we had a problem with the belts was this year was at battlecry, we actually snapped one of them. Besides that we havent had a single problem. The belts actually made our drive train stronger because they have more endurence than chain. I think it would be a safe bet to say that we will be useing belts on our drive system this year also.

Tom

Re: Timing Belt Drive System
 

Can you give us some specifics on the belts you use? Where do you get them? What are they made of?

Thanks
Matt B

Re: Timing Belt Drive System
 

We get out belts from brecoflex.
http://www.brecoflex.com/?CATID=1&SC...codeNa me=BFX

I am preaty sure this is the model that we use.
I do know we use the 4mm belts.

if there is any more questions about the belts or our drive system just send me a PM.

Tom

Re: Timing Belt Drive System
 

Timing belts are good, but in my experience they are a little touchy to use. They're great due to weight and size (aluminum pulley=yay), but for rapid direction changed and high tourque applications, aka a FIRST bot driving offensively around a field, they ahve a tendency to slip and chatter. When driving with a skid steer system, the rapid, high speed direction changes have a tendency to make the belt jump a couple teeth, which will wear them down quite quickly.

As for stretching, as long as they aren't over-tensioned, you won't notice any stretch duting the time of a FIRST season.

As for belts for non drive base use, I say go for it, they rock because of weight and size.

Re: Timing Belt Drive System
 

The only additional advice I can offer is that to be sure your design allows for fast & easy belt changes. If you need to remove three wheels to change a belt, it'll be a problem when you have to. On the other hand, if you just need to release the tensioner, slip on a new belt and go, you've done your homework.

Don

Re: Timing Belt Drive System
 

As someone else has pointed out, belts with teeth have been used on motor cycles, instead of chain, to drive the back wheels.

Not little scooter bikes, big bore street rockets - and they dont slip or jump teeth, even when you smoke the back wheel for 200 yards down the street

not to take anything away from other teams that had trouble with belt designs, but (like everything else in engineering) you have to get the design and implementation right.

One thing, you want at least 180º wrap around each pulley in the system. This is great for two pulleys - when you try to hit three wheels + a drive pulley with one belt, then things get tricky.

Also, Ive been told the new notched belts only stretch a little after they are first installed. You re-adjust the tension after several hours of use. After that it will not stretch anymore.

Besides being light and strong notched belts have one other unique quality - they are very quiet. We all know that with mechanical systems, once all the noise has leaked out, the system quits (therefore quiet running mechanical systems last much longer :^)

Re: Timing Belt Drive System
 

I have to strongly disagree with you.

Maby you are using the wrong belts because with the Breco-Flex belts we use we have had no such problem. We have never slipped a belt during a match or chipped the tooth of a belt. The only problem we have ever had was a belt snapped once in an off season event which i still don't under how 10 steel support rods that run through the whole belt can be sheered.
We buy our belts and the pulleys from the same company so that they mesh perfectly.

Tom

Re: Timing Belt Drive System
 

This is how we did it this year (We tried friction belts instead (BAD IDEA). We created a model of this too using timing belts but it was never fully implemented onto the bot. From what we played around with it, it worked wonderfully. Turning is the one spot you have to watch out for. When you use belts, you may get too much traction onto the carpet which could, in result, make turning a lot more difficult.



We used 80" belts if i remember correctly. We had 1 drive pully (center) and 4 idlers. Instead of using a series of wheels on the bottom, we decided to use slides.

The nice thing about using belts is it makes the connection to the gearboxes a lot simpler.

Re: Timing Belt Drive System
 

Timing belts are great, no doubt, but if you put them on your drive train and though your match to match use will work out well, look at it over the entire tournament. As your days go on the belts wear down and eventually run the risk of stretching. A place of high use in your robot like your drive train is not the greatest location for a timing belt. Drive trains simply go under too much stress too frequently to balance out the pluses and minuses of timing belts. A better example of a good use of a timing belt would be like tyeing your shooter wheel to your motor.

For the record, motorcycles use Timing Belts and Chains, sport bikes generally have chains whereas cruisers usually have belts.

BTW while researching to find what type of chains bikes generally use, I stumbled across a very interesting article.

Re: Timing Belt Drive System
 

Im not sure where you are going with this. Cruiser bikes have 50 to 150 HP engines, pulling on that belt drive system

the total power available to a FIRST robot, using all the motors, is about 2HP.

If you can drive a motorcycle with a 150HP engine thousands of miles, for months at a time, without needing to touch the drive belt, then I think we are safe with the same belt system on our 2HP robots, running a couple hundred 2 minute matches throughout the season.

Re: Timing Belt Drive System
 

The big difference though is that the motorcycle isn't subject to the same forces that a robot is when it's on a field in competition. You don't see too many motorcycles getting side impact crashes and still running properly. Robots get hit a lot, so they need a system that is more likely to still run properly after being nailed in the side while running.

If a robot wasn't subject to bumps and bruises that come with moving around on a playing field, I'd have no doubt that they'd be able to run for a long time. But they are subject to those forces so things are more likely to break.

Re: Timing Belt Drive System
 

I dont think the hits our robots take come close to the forces on the drive belt of an 800 lb motorcycle

when the rider revs the engine up, and dumps the clutch to spin the wheel - you are talking about 100 HP directly loaded up on that belt

or someone who is not coordinated, shifting incorrectly - transferrring the momentum of the motorcycle back to the transmission, through the drive belt

or making a panic stop - hitting the brake and locking up the back wheel - stalling the engine through the drive belt

the amount of forces on a motorcycle drive belt are far beyond anything you can get on a FIRST robot.

If your robot is hit and the drive system is knocked out of wack - you bend a frame member that is holding a pulley in alignment, or you knock the belt tension wheel out of postion - then yes, your belt drive system cannot work if the pulleys are no longer aligned

but that is true with any mechanical energy transfer system - chains, gears, drive shafts... Your drive train must be installed on a robust chassis if you expect your robot to keep working after you mix it up with other bots on the field.

Re: Timing Belt Drive System
 

I've got a bike that took a nice 40 mph dump onto asphalt I'd like you to meet. That was a fairly severe side impact.

It was fine. Me, not so much. It took a lot longer to get my self up and working then it did for me to pick up the bike and get it started. The belt driven transmission was fine, as was the chain to the wheel.

Belts are a fine way of transferring power in a robot. Like chains, gears, drive shafts, viscous couplings or any other means of transmission they require some care and attention on you're part. But no one said this robot stuff was going to be a cake walk.

-Andy A.

Re: Timing Belt Drive System
 

Something has been bothering me about the drawings that were posted by a few people for proposed belt drive systems. I just figured out what it is.

The serpentine belt on the AC and alternator on a car only spins in one direction. The drive belt (or chain) on a motorcycle wheel normally only supplies force in one direction (unless you let off the throttle to slow down)

those systems are ok with spring tensioners to take up the slack. But for a robot drive train that goes both ways, the side of the belt that is under tension would pull the slack out of the tensioner. When you reverse directions it will pull the slack to the other side.

This is not good. That would introduce slop into the system. You want your wheels to turn together, to supply force together. As the spring tensioner is pulled tight on one side, then on the other that will make the wheel on the other side of the tensioner turn unsynchronized to the rest of the drive train.

So Im thinking you dont want a spring tension system - you want something that is adjusted manually, a lead screw sort of thing, that wont flop around when the robot reverses direction.

Re: Timing Belt Drive System
 

In our tread Modules Shown Here We Just use a 3/8-16 bolt to push on a plate that is connected to the shaft of one of our pulleys for tension...Like this.