pic: FRC 1771 Drivetrain

This is my version of the west coast drivetrain.
Stats include:
5" custom uhmw wheels
Custom 2 speed transmission with direct drive to center wheel (6.5 and 16fps)
Outer wheels connected with timing belt
Tensioning accomplished by tightening a bolt at the end of each side sliding the bearing block
Sheet metal bumper mounts for easy removal and protection
Total weight is ~32lbs

Let me know any feedback

What ratios of gears are you using on the gearbox and it looks very promising. If you have access to a CNC, might want to lose some weight.

You might want to support the bumpers at the ends. Otherwise they’re likely to rub on the wheels, causing problems.

This was a problem for us this last season, and is one of the reasons why we probably won’t do cantilevered wheels again.

Thanks for the advice. This will be done on a CNC so lightening patterns may show up on this if we decide to do it. Although ~35lbs for a drivetrain may prove that reducing weight is unnecessary.

I will take into consideration the issue with bumpers flexing.

On a seperate note does anyone have any experience with UHMW wheels, specifically in a cantilevered scenario like this.

every ounce matters dude, ask us. we were 4 pounds underweight and we got to atlanta, over by .1 pounds. also what are the ratios for the gears you used to achieve your fps? stick with aluminum wheels or andy’s new plaction wheels. if you have the time, do uhmw wheels for the pre season. one of our capitans made them when he went to college and said that they need tread on them and that they last for a long time. the wheels were used on a go-cart.

Yeah I will look into cutting weight out of the frame. As for the wheels, I really want to go custom for a lot of reasons. Primarily we can get the exact size we want (5"), they are also keyed for hex shaft without a hub, and finally they are way cheaper as the material to make 12 wheels only costs ~$70. The wheels will of course be treaded with roughtop or wedgetop. I guess I am primarily asking for the durability of the actual uhmw portion of the wheel and if we go this route we will probably have a full set of spares with us at all times

I would be concerned about losing the bumpers with you’re bumper mounts. I looks like if you got into a good pushing battle that you’re bumpers could end up coming off.

Also, one of the big benefits for the west coast drive is it’s maintainability. When designing something always ask yourself what do I do if X breaks, how do I repair or replace X? What happens if you break a belt? Right now it looks like you’d have to remove and disassemble part of the transmission in order to do that. That’s probably going to be a lengthy repair. I would recommend using 25 chain instead.

Even if the numbers are in your favor, it’s best to have the ability to repair something rather than leave it to chance. You never know what could happen.

Anything that can go wrong, will go wrong and yeah: use #25 chain (weight saver).:smiley:

Yes in order to change a belt the transmission would have to be removed. I figure the entire operation would take slightly longer than putting on a chain however the weight savings for a belt versus even #25 chain is pretty significant. This would be something that we would really have to weigh the tradeoffs on before deciding. Plus the belts really have a cool factor and Ive been wanting to try them for a while.

I don’t think 25 chain is lighter than belts, I would just use 25 chain to make the drivetrain easier to maintain. Another thing to consider too is that belts will stretch more than chain. This means that the slots that the front/read bearing houses sit it will have to be longer to pick up any slack created from the stretching.

Belts will break, a team posted that and it happened at the San Diego Regional. Chain is the way to go unless you have an expert helping you. Also, belts need to be tensioned before and after each match, this may become bothersome after a few matches. FIRST gets interesting and people tend to forget minor things, I know my team did. Ahh the good times.

Actually belts stretch much less than chain. In multiple posts by team 125 they talk about there belts not stretching at all after initially tensioning them. they rely on kevlar belt which is very strong stuff. The only positive I see to the chain is that it is easier to change if it breaks. In all other aspects, belt is the superior solution.

I forgot to post the gear ratios so here goes. The first stage is 12 to 48 reduction, and then the second stage is either a 15 to 60 or 30 to 45 reduction.

Other than needing to loose a few pounds, i would say it looks good. Keep up the good work. :slight_smile:

My bad, i was talking about fatigue of the belt. They are just plastic, belts are great if you can use them and chain is just a tad bit easier to maintain and good luck with whatever you go with. BTW, nice cad job.

Im hoping I can get this drivetrain under 30 lbs. I havent made one yet that could actually function that was that light. Im working on a single speed version in case there is no need for a shifter like this past year.

I’m worried about hex-broaching plastic. Doesn’t seem like a good idea to me. Might want to go with some of those Al AM hubs… or wheels…

For the record you CAN buy 5" plastic wheels for less than $70.

Yeah, I agree with Hachiban. Hexing UHMW is harsh, our capitan put ball bearings in them and it worked fine, but hexing is a different story. Where can you get 5 inch plastic wheels???

35 pounds is a very admirable weight for a rolling drivebase. Very few teams have made theirs lighter.

I don’t know of any place to purchase 5" plastic wheels from other than colson wheels which are not hey keyed and which do not allow for tread attachment. Also the price of $70 is not per wheel that was the approximate price that itwould cost us to make 12 wheels, enough for 2 robots.

Has anyone actually tried broaching UHMW or any plastic for that matter? I would think it wouldn’t be a problem but if that is not the case then I have to change my plan.

I agree and was under the assumption that anything under 35lbs or even 40lbs is a light drivetrain. I now have 2 drivetrains designed under 35lbs, one cantilevered and the other using plates and standoffs.