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Unread 01-09-2008, 23:45
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Re: pic: FRC 1771 Drivetrain

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Originally Posted by sdcantrell56 View Post
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.
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Unread 01-09-2008, 23:56
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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
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Unread 02-09-2008, 01:21
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Re: pic: FRC 1771 Drivetrain

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Originally Posted by sdcantrell56 View Post
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'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.
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Unread 02-09-2008, 01:35
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Re: pic: FRC 1771 Drivetrain

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Originally Posted by Hachiban VIII View Post
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???
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Unread 02-09-2008, 16:43
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Re: pic: FRC 1771 Drivetrain

The frame looks great, nice and simple, and the bumper mounts are a very clever approach. I'd avoid cheese-holing it if I were you... It's already very light! Just put as much thought into your mechanisms as you did into this drivetrain and you won't have any weight problem at all.

And belts are awesome!

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Originally Posted by rc_cola1323 View Post
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???
$6-7 a piece (about $15 each if you get them with aluminum hubs):
http://banebots.com/c/WHB-HS6-498
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Unread 02-09-2008, 17:05
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Re: pic: FRC 1771 Drivetrain

Those wheels are definitely worth a look however I am going for something with a bit more traction (roughtop). I am also debating doing a finesse version of this one using custom omni wheels in the corners and a center traction wheel plus single speed. I just finished my single speed and with it I have gotten this drivetrain under 30lbs (~29.5)
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Unread 01-09-2008, 23:58
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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.
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Unread 02-09-2008, 00:01
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Talking Re: pic: FRC 1771 Drivetrain

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Originally Posted by Jon Jack View Post
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).
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Unread 02-09-2008, 00:07
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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.
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Unread 02-09-2008, 00:10
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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.
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Unread 02-09-2008, 00:19
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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.
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Unread 02-09-2008, 00:26
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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.
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Unread 02-09-2008, 00:29
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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.
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Unread 02-09-2008, 00:32
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Re: pic: FRC 1771 Drivetrain

Other than needing to loose a few pounds, i would say it looks good. Keep up the good work.
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Unread 02-09-2008, 00:35
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Re: pic: FRC 1771 Drivetrain

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Originally Posted by Brandon Holley View Post
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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