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-   -   pic: FRC 1771 Drivetrain (http://www.chiefdelphi.com/forums/showthread.php?t=69012)

sdcantrell56 01-09-2008 14:50
pic: FRC 1771 Drivetrain
 

R.C. 01-09-2008 14:51
Re: pic: FRC 1771 Drivetrain
 
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.

=Martin=Taylor= 01-09-2008 15:08
Re: pic: FRC 1771 Drivetrain
 
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.

sdcantrell56 01-09-2008 22:58
Re: pic: FRC 1771 Drivetrain
 
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.

R.C. 01-09-2008 23:45
Re: pic: FRC 1771 Drivetrain
 
Quote:
Originally Posted by sdcantrell56 (Post 763674)
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.

sdcantrell56 01-09-2008 23:56
Re: pic: FRC 1771 Drivetrain
 
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

Jon Jack 01-09-2008 23:58
Re: pic: FRC 1771 Drivetrain
 
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.

R.C. 02-09-2008 00:01
Re: pic: FRC 1771 Drivetrain
 
Quote:
Originally Posted by Jon Jack (Post 763687)
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).:D

sdcantrell56 02-09-2008 00:07
Re: pic: FRC 1771 Drivetrain
 
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.

Jon Jack 02-09-2008 00:10
Re: pic: FRC 1771 Drivetrain
 
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.

R.C. 02-09-2008 00:19
Re: pic: FRC 1771 Drivetrain
 
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.

sdcantrell56 02-09-2008 00:26
Re: pic: FRC 1771 Drivetrain
 
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.

sdcantrell56 02-09-2008 00:29
Re: pic: FRC 1771 Drivetrain
 
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.

Dancin103 02-09-2008 00:32
Re: pic: FRC 1771 Drivetrain
 
Other than needing to loose a few pounds, i would say it looks good. Keep up the good work. :)

R.C. 02-09-2008 00:35
Re: pic: FRC 1771 Drivetrain
 
Quote:
Originally Posted by Brandon Holley (Post 761870)
Thanks for the shout out akash.

While I am no expert, I did spend a considerable amount of time this past season working with belts. We used .200" pitch, .375" wide kevlar reinforced timing belts from www.sdp-si.com. We finally had a belt go down after the beantown blitz this year (2 regionals and 2 off-season events).

The thing about a belt is even though ours were kevlar reinforced, they are just plastic teeth. Keeping them tight will help a considerable amount, and I am pretty sure you guys did to have the belt(s) last as long as they have.

http://en.wikipedia.org/wiki/Fatigue_(material) <---- FATIGUE.

Fatigue is basically repeated stress over a relatively long period of time. Even though your belts may not have seen any greatly large shock loads, seeing small loads over an entire FIRST season probably fatigued the material in the belt enough that it finally broke.

Congrats on making it this far into a season before having to change them!

Hope it helps.

Brando

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.


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