Team 1671: Off-season belt drive prototype
 

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Here is the prototype that the 1671 CAD team has put together.
It is driven by two standard tough box transmissions (for now).
The dimensions are 26.1 inches wide X 36.75 inches long, and only 5.46 inches tall.

It uses timing belts instead of chain to power the wheels.(sprockets and belts from sdp-si)
The system was inspired by team 1625's internal belt drive, and the tensioning system was modified from team 114's, the cool thing about it is the ability to tension the belt system externally.

We would love to hear what you guys think about the design.

Thanks :)

Re: Team 1671: Off-season belt drive prototype
 

Looks like a great drive base! We used a timing belt drive on our Lunacy robot and it was rock solid. We're still running it as a development and demonstration base. Ours actually doesn't have a tensioning system though.

Re: Team 1671: Off-season belt drive prototype
 

Thanks, the team has worked really hard.
Really, that is great to hear. Yeah a lot of our mentors have been bringing up belts for a couple years now, and we wanted to take a different direction in 2011. They also save a lot of weight if your sprockets are good.

Re: Team 1671: Off-season belt drive prototype
 

I'm not going to comment on the use of timing belt, as our team hasn't had experience with it. I do, however, have a few general questions and comments.

What size axles are you using? They look like 3/8", but I'd highly suggest 1/2" for cantilevered wheels. Also, What is the point of the diamond shaped bearing blocks? It would be much better for manufacturing if they were simpler.

Other than that, looks pretty cool. Good luck!

Re: Team 1671: Off-season belt drive prototype
 

Yeah, all of the axles are 1/2" with cantilevered wheels 3/8" would be really bad. :eek:

As far as the diamond shape it was mainly for looks, team 114 used a simpler square sliding block, we may need to change this when we begin manufacturing, but we will definitely look into that.

Thanks

Re: Team 1671: Off-season belt drive prototype
 

If it has no function, it shouldn't be there.

I'm with eugene, make them square.

I'd also say lose the pocketing on the crossmember and switch them to 1/16" wall. I can see why with teh slots you can't run 1/16" on the siderails, but I'd recommended losing the pocketing there as well. There is a lot of work invested in such pocketing, and without much gain.

Heavily pocketed 1/8" is actually weaker than solid 1/16", and often a bit heavier.

Re: Team 1671: Off-season belt drive prototype
 

Yeah they have been modified to be square now, it was a really simple fix.
This is our first time using aluminum tubing (and welding) usually we are a 100% sheet metal design. I will definitely fix the tubing.

Do you know of any good sites to purchase square and rectangular tubing with a 1/16 inch thickness. I just got the ones on the bot from Mcmaster, but for 1/16 inch tubing they only have 1inch X 1inch.

Thanks

Re: Team 1671: Off-season belt drive prototype
 

Shaker's working on a pretty similar prototype (but even shorter!). Insert your favorite variant of "great minds think alike" here.

I too think the lightening is a bit of a stretch. Taking material out of the sides (especially the sides perpendicular to forces in a box tubing scenario) weakens it a LOT. Considering you can cut a bunch of weight with square bearing blocks I would do that.

If you can think of a way to tension the blocks without using sliding bearing blocks, you can use unpocketed 1/8" tube to support your bearings. A lot of teams ran cantilevered wheels off of Toughbox Nanos last year which are made of the same stuff. This could save you a little weight and a lot of strength considering how aggressive your pocketing is around the bearing blocks.

However, unpocketed 1/8" tube for a whole rail is pretty hefty, so you may want to use 1/16"... but 1/16" of material is not a lot to hold a bearing with!

Re: Team 1671: Off-season belt drive prototype
 

Coast aluminum, is great in California. We buy their sharp corner 6061 (NOT 6063!) square and rectangular. We also get a lot of round tubing from them.

There are other great metal suppliers in CA, but we've always been happy with Coast. Maybe ask 1323 what they use, they're much closer to you as you know.

Re: Team 1671: Off-season belt drive prototype
 

I don't understand that part. We use sliding blocks in 1/8", what would the issue be?

In fact, we use 1/8" purely because of the sliding blocks, and it's usually the only 1/8" on our robot!

Re: Team 1671: Off-season belt drive prototype
 

Thats cool that you guys are doing something similar, I hope you post it up.

Yeah I see what you are saying about the thickness, 1/8 without pocketing would weigh a considerable amount. But I need to make sure I can find a supplier for the tubing we need (2inch X 1inch, and 2inch X 1inch) that has those dimensions in 1/16inch thickness.

Re: Team 1671: Off-season belt drive prototype
 

I'm saying if one wanted to opt out of using bearing blocks, bearings would be adequately supported with 1/8" tube; otherwise you could step down to 1/16" tube without many problems.

Re: Team 1671: Off-season belt drive prototype
 

I am not familiar with welding parts. Is it okay to use 1/8inch on the outside rails, and 1/16inch in the support bars?

Re: Team 1671: Off-season belt drive prototype
 

Yup! and 2x1 is easily available in 1/16". You said 2x1 twice, what was the second size you meant?

I'm a big fan of efficiency. If you have to use 1/8" for the siderails, yes you *could* pocket it, but often that time and resources is better spent elsewhere. We compensate for this by extremely aggressive in parts that are easy to add pocketing to (all the plates that we get waterjetted, where pocketing is trivial to add). Although we get our framerails CNCd because we get a lot made, we have them designed such that they could be made on a manual.

Don't get me wrong, it's a good start, just trying to help you out.

Just curious, why have the double opening frame? You may want to close one end, if the game switches back to 06-09 bumper rules, you'll need some support there anyway. you may want to design in 6" segments on the intake side for that reason as well, and a bumper support system for the siderails. Never hurts to figure this stuff out a head of time so that it is well integrated into your design.

Re: Team 1671: Off-season belt drive prototype
 

How could you cut weight by adding more material? I don't think I'm quite understanding what you're saying.

Re: Team 1671: Off-season belt drive prototype
 

I think he means using nonsliding bearing blocks in 1/16" would allow you to not have to use 1/8".

I also think what he was getting at was using sliding blocks in 1/16" wouldn't work (which I agree with).

Re: Team 1671: Off-season belt drive prototype
 

Okay thanks.

Oops I meant 2inch X 2inch, I am just distracted by the smell of all the food here for thanksgiving I made a mistake.

Re: Team 1671: Off-season belt drive prototype
 

Aren Hill would certainly disagree, but I think you should switch to 2x1 rather than 2x2, and have the belts outside the frame (similar to a "west coast drive"). I see no advantage to hiding the belts and making repair, maintenance, etc. extremely difficult.

Re: Team 1671: Off-season belt drive prototype
 

Our setup has the belts in the tube largely from our chosen gearbox arrangement, which is arranged how it is due to manufacturing capabilities.
So there is some reasoning behind our madness (occasionally) .

If we were direct driving with a toughbox we'd probably have the belts on the inside face of the frame rail similar to most WCD's.

Also ours is still in the experimental stage and follow at your own risk

Re: Team 1671: Off-season belt drive prototype
 

If you're already using 1/8" tubing, you can omit bearing blocks if you don't have a reason to use them. This cuts a small amount of weight from a system that used 1/8" tubing with bearing blocks. Adam covered what else I was trying to say (not doing a very good job of communicating today).

Re: Team 1671: Off-season belt drive prototype
 

Here is the second revision, thanks for everyone's advice, I believe most concerns have been addressed.

Once again thank you guys for your help. :)

Re: Team 1671: Off-season belt drive prototype
 

I would ditch the slots above the bearing blocks, combined with the bearing slots they are really weakening the fraem there.

Also, rather than cutting clearance in 2x1, you can also just use 1x1 and center it on the frame.

Other than that, it's massive improvement over your initial design! Keep it up!

For the gearbox, it may b easier to bolt a small plate to the frame rail, and then use on set of bolts to go through all three plates with standoffs (the two roughbox plates, and the mounting plate).

Re: Team 1671: Off-season belt drive prototype
 

I understand what your talking about when it comes to the 1x1 frame on the front support in the center of the frame. But what happens if the belt somehow manages to break? Wouldn't that render an incredibly difficult or near impossible task to fix?

Re: Team 1671: Off-season belt drive prototype
 

My main criticism is that it looks exactly like the first iteration of my drivetrain I was working on over break :(

Now I have to skip a revision and work on a new one :P

Re: Team 1671: Off-season belt drive prototype
 

It wouldn't be impossible at all. Instead of welding that brace have it bolted on.

Drive looks great, can't wait to see it built.

-RC

Re: Team 1671: Off-season belt drive prototype
 

Sorry for my understanding I thought they were welding the frame together...

Yes possible if bolted, but they mentioned welding which is why I pointed that out...

Re: Team 1671: Off-season belt drive prototype
 

Okay here is the revision number 3. I added in L-brackets for the front bar, to run the belts over and under it. I did say that we were welding, but when I changed the dimensions of the bar I just dropped brackets in. Also I fixed the transmission mounts.

Thanks again

Re: Team 1671: Off-season belt drive prototype
 

Looking good, the gearbox mounts could probably be 1/8", or pocketed.

Curious, what are the slots over the bearing blocks for?

I did totally miss the whole belt around frame member thing, Make sure you leave the ability for quick replacement.

Whats nice about this setup is its trivially easy to change it for a super shifter rather than a toughbox.

Re: Team 1671: Off-season belt drive prototype
 

Okay thanks for the tip. Oops the slots were supposed to be gone, they were originally for getting access to the internal belts, but those are gone now so they should be deleted.

Yeah I wish we had enough time to create our own shifter but we are a little short on time.

Re: Team 1671: Off-season belt drive prototype
 

The system design is what matters. It little sense to do custom shifters before you have every aspect of the robot covered; the decision to use COTS gearboxes is a good one!

Keep it up, the progress you've made today is great.

Re: Team 1671: Off-season belt drive prototype
 

Tiny nitpick: right now the set of timing belts on the closed end is closer to the 1x2, while the set of timing belts on the open is farther from the 1x2. If you make the open side closer to the 1x2, it will increase the area you have for your intake mechanism.

Re: Team 1671: Off-season belt drive prototype
 

haha thanks for catching that. That could really give us some extra room.

Re: Team 1671: Off-season belt drive prototype
 

If you are going to put your belts around a frame member, changing them in the unlikely event of a breakage or the slightly more likely event of a broken tooth would be impossible (welded connection) or at least a pain in the butt (bolted connection).

Since timing belts weigh next to nothing anyhow, if you choose to go this route you may think about leaving a set of spare belts (fastened down out of the way) already around that cross member, just in case you need to swap it out. In this way, changing a damaged belt is as easy as sliding your bearing block, switching the belts, removing (cutting) the damaged belt, and re-tensioning the bearing blocks.

Re: Team 1671: Off-season belt drive prototype
 

Also, what pitch, belt width, and profile are your belts? 5mm pitch, 15mm width, and either HTD or GT2 profiles seem to be the most common belts for FRC drivetrains. You may be able to get away with 9mm belt width, but given the negligible difference in weight I would just go with 15mm.

One other reminder about your choice of pulleys: be careful how small you go. Belts fatigue faster when bending around tight radii in general, and all the design documents I've seen suggest at least 6 teeth in contact with the pulley at all times. An engineer on our team who designs timing belts for a living recommends using at least 2" diameter pulleys for HTD belts (it looks like that's about what you are using). And double flanges on every pulley is a must for FRC (again, looks like you already knew this!).

Great job!

Re: Team 1671: Off-season belt drive prototype
 

I'm really curious about your shaft and bearing setup, would you mind posting a cutaway of that?

If a 6" bumper segment is required, this gain is kind of negated though. In that case I'd run it how he had it to get more electronics space.

Re: Team 1671: Off-season belt drive prototype
 

This may be a terrible idea, but why not run the outer run of your belting inside the tube? With a single cantilevered run and a single internal run, you can fit the assembly entirely within a 2x1 tube, and you could change the belts by pulling the live axle at the end out.

(At least, that's what I'm doing in my theory - not - fact - at - all model)

Re: Team 1671: Off-season belt drive prototype
 

Why run the belts internal?

I've yet to hear a clear advantage to such a setup; and there is a very clear disadvantage (your belts are INSIDE the tube).