Timing Belt Drive System
 

We are looking to build a timing belt drive system and I was wondering if anyone has built one out there.

What type and size of belts did you use?
How many wheels were in the drive system?
How did you tension the system?
What problems did you have?

Just curious what peoples experiences have been with a drive system like this.

We are planning on making a six wheeled drive system with spring loaded tensioner and serpenting the belt around the drive sprocket and the wheels. I haven't looked at had size or profile of belt we are going to use yet. We plan on using about 8" drive wheels with about 7" wheel pulleys. Yes we plan on either having spokes on the wheel pulleys or making them hub-less. We are planning on using live wheel with fixed axle and attaching the wheel pulleys to the face of the wheels. We have not decided on what wheels we are going to use ideally we will use a fully custom wheel made at our machine shop and then rapped with rubber from a local rubber mill we work with.

Thanks for the feed back.

Re: Timing Belt Drive System
 

Maclaren,
This is purely my opinion and in no way am I forcing my answer towards you, I also appreciate this community and the fact that we are able to hold discussions and have ones opinions posted with utmost respect.

I don't believe a belt drive is effiecient enough for a few reasons

• It would require a custom made belt, while #25 or #35 chain is cheap and is customizable
• Belts tend to slip, and with a drive system in FIRST, you want your wheels to slip, and not your drive system.

My former team in 2002 made a two speed transmission out of belts, and it was a complete failure. If I was in your shoes, I'd use chain for my drive system (it's a proven system) and not design the most crucial part of any FIRST robot with questionable variables.

Again, this is my professional opinion, and I thank you for the chance to respond to you.

Sincerely,
Greg Perkins

Re: Timing Belt Drive System
 

Thank you for the response.

I welcome design critique and plan on always welcoming it.

The reason that we don't want to use chains is that we have stretched several chains before which is a big pain in the butt.

Also chains are heavy compared to belts. Sprockets are also heavier than pulleys.

The amount of tensioning that we have built in can compensate for the difference in standard length belts. So I'm confident that we can find one that fits.

Also we are going to make sure to serpentine the belt around the drive pulleys as much as possible to eliminate any chance of the belt slipping.

I have attached a sketch of what we are planning on doing.

If you are asking yourself about the engagement of the center wheel pulley yes that is a concern but it can be compensated for with additional idler pulleys around the wheel.

As for the actual transmission that will drive the drive pulley it will be two cims that are geared together and attached to the drive pulley. We plan on making the drive pulley either out of aluminum or steel and it will have a large mating cross-section with the output shaft from the gearbox.

Re: Timing Belt Drive System
 

Maclaren, my old team 108 tried to use belts in 2003 and 2004 instead of chain simply because of the weight issue. 2004 was nothing but a huge mess. I have looked at the sketch you attached with your post. In theory it works (we had it done very similarly in 2004), but in reality it didn't. At the same time in 2003, team 108 used belts and pulleys and was very successful. It really depends on how you design the chassis.

The 2003 robot was a 4wd, and the whole front module would go back and forth horizontally in order to tension the belt (using a quarter inch 4" long bolt). On the other hand, the 2004 robot (4wd) had the tensioner tension the chain vertically which failed.

At this point, what I would suggest is design the chassis, post it up here on the forum and let Andy Baker, John V. Neun, Paul Copioli, Ian Mackenzie, Tim Baird have a look at it. There are many other engineers, mentors, and students who will help you perfect your design.

Here is a picture of the 2004 chassis. I couldn't find a 2003 one, when I do, I will post it here.

Also when you get a chance, please read this thread

Re: Timing Belt Drive System
 

There's a reason you don't see more belts in place of chain of FIRST robots. It's a brutal field out there.

Re: Timing Belt Drive System
 

Well, success or failure - you'll learn something.

The Stock Drive website has alot of good information about timing belts and pulleys. Reading through it will give you a bit more information. Belt size, tooth profile, pulley types, and more will all effect how much power you can transmit and at what speeds. Also have an effect on belt streach and such.

http://www.sdp-si.com/Sdptech_lib.htm

Don't forget, timing belts drive motorcycles.

I don't know if a belt drive system will work - I haven't done the math. But I think it's worth the thinkin' time.

Re: Timing Belt Drive System
 

I haven't touched timing belt since 2002 and had limited success at that, but I can see its appeal. The single largest issue I had to overcome in both 2001 and 2002 was preventing the belt from walking off the pulleys.

Out of curiousity, since it appears as if you're striving simply to replace roller chain with timing belt, have you considered taking things one step further and replacing the wheels with timing pulleys? It aggravates the problem mentioned above, but there are self-aligning belts and things that I've never been able to play with that may alleviate some of that concern. If there's a simple way of keeping your belts on, it'd seem a no-brainer to save even more weight by riding directly on your pulleys rather than attaching them to a wheel.

Re: Timing Belt Drive System
 

Maclaren, I do see how you want to save weight, but as I look at it, I would like to see most of the weight put into the drive system. Sure, I may be bias because I drive the base but you need a solid drive system to get around a FIRST field now-a-days. Chains do weight quite a bit more then belts, but chains don't stretch typically, unlike belts that stretch more commonly. As Greg said, belts slip, chains dont, in the game of FIRST you would most commonly like to see the wheels slip before the drive system itself. However, I think it would be a cool endeavour but you may find out that it will give you periodic problems throughout the year. It may be cool to do in the fall, as a team building activity to train new team members.

On a bit of a sidenote, a different type of drivetrain done in the past was a ball drive. It used metal pads to turn the balls, and chains to power the omnis. It was my teams "show bot" that was only used in a few matches during the 2003 season.

Re: Timing Belt Drive System
 

Nice design concept. I think it is great that you are looking at different solutions. We all need to do some of that to get progress.

I have a couple of comments/critiques based on your sketch that I hope will be helpful;

1. You mentioned using timing belts. That usually means cogged or toothed belts. Is that what you intended? One potential problem is that you have your drive pulley contacting the outside surface of the belt while your wheel pulleys contact the inside surface of the belt. With this kind of arrangement you would need to use a belt that is cogged on both surfaces.

2. Your drive pulley is pretty small. You will lose a lot of efficiency trying to drive a belt around a radius that small.

3. This one is a little complicated. A cogged belt is like a chain. It has discreet positions that it contacts at (IE. if the belt is held still you can turn the pulley 1 tooth but not 1/2 of a tooth) The way your design is now you have the center wheel pulley contacting the belt in 2 discontinuous positions. Let's say that the teeth on the bottom of the middle pulley are meshed with the belt. Now we will trace along the belt around the drive pulley and the back pulley and get back to the contact point between the belt and the top of the middle pulley. What is the chance that the belt teeth will be "exactly" lined up with the pulley teeth?

Don't give up. I believe that high strength timing belts are quite viable for FIRST robot drive-trains (I haven't convinced my team yet).

Good luck.

Matt B

ps
here is a concept I have been batting around my head. It is very far from finished, but maybe it will start some thoughts.
[IMG]belt drive system.jpg[/IMG]

Re: Timing Belt Drive System
 

If you are going to use timing belts, why use wheels?

There are many teams, Team S.P.A.M. included, who have used timing belts as treads.

Recently, we went to a dual tread design so if one tread should break during a match, you can still drive around. It works quite well.

Re: Timing Belt Drive System
 

I've always thought the belts that drive blowers like on dragsters would make good tank treads. But then again, unelss you are climbing stairs, I see no purpose for tank treads.

Re: Timing Belt Drive System
 

The Aztech's, Team 157, used timing belts and pulleys on their 2005 robot. As far as I know, they didn't seem to have any problems with them. They used some fairly beefy belts, 1-1/4" to 1-1/2" wide, with a 3/8" or 1/2" pitch. They look to be fiber reinforced, so I can't comment on their strength. However, it was not a continuous loop, as the bot had two belts per side in a 4wd setup.

I'm waiting for a couple pics to be uploaded, stay tuned for links. :)

BEN

Re: Timing Belt Drive System
 

If your going to go that far, wouldn't it be worth it to just go all the way to treads? Although I can See the advantage of just having the wheels.

Also, why not have a spring tensioner on one side and just drive the middle pulley.

Re: Timing Belt Drive System
 

I am from team 157 and the belt system worked so well in 05 that we went with it in 06 we get all the belts and the pully stock from the same company and the belts mesh perfectly so there is no chance of sliping and in 2 years we only changed 1 belt and that was because we got another bot inside and it got scratched and we didnt want to chance it. but this was a huge difference form the many chains i changed sophmore year on our bot. once you go belts you wont go back

Email me if you are intrested in detials pics company names or whatever
xtreme19881@aol.com

tag it belt help or something to that effect

Re: Timing Belt Drive System
 

Here is a resource for belts in general. Brecoflex...they sell belts to custom lengths and pulleys with Self tracking profiles...commonly used for tank treads but you might be able to find something your looking for in timing belts.

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.

Re: Timing Belt Drive System
 

Excellent point Ken

One important thing to keep in mind is that you normally see spring tensioners in friction drive systems and in situations where the belt/chain length might change. It a timing belt application you have a positive drive system, not a friction system, and a steel reinforced are even a nylon reinforce belt will have basically no stretch. There is no need for a spring loaded tensioner. All you need is to be able to move one of the pulleys to take up any slack that comes from manufacturing variation. If your drive system is simple enough you may even be able to design it with no adjustment. If you have ever torn apart the from end of an overhead cam engine you would see what I mean. They often use a timing belt with no provision for tensioning.

Matt B

Re: Timing Belt Drive System
 

Seeing as Steel re-enforced belts such as Brecoflex belts dont stretch much under the forces a robot can put out I wouldn't want to be the one to try to put on a belt(esp. one with a self tracking Profile)onto anchored pulleys and strech it with my bare hands or even a tool to get it to slide over said pulleys. It truly would be easier to implement a Screw Tensioner on one of the pulleys and have the ability to start from slack and turn a bolt and go to a nice useable tension(not to tight).