Hi all, this is the fourth year for our team and every year the same questions comes up. We have always used 35 chain and corresponding sprockets, but I can’t help but feel they are oversized for the job. Last year we had the drill and atwoods coupled driving 8" wheels at 5-6 FPS not the fastest, but definitely not the slowest. With the wheels we had we got about 160#s of thrust to the carpet.
So, what do you all think? Has anyone had trouble with 25 chain and small sprockets?
What would be the smallest number of teeth that we could run safely? 12, 15, 18???
Were planning to use both drill and atwoods again with a shifting gear box.
Our transmission spins quite a bit faster this year and one of the problems with the 35 chain is that we really need to use at least a 4:1 reduction with the chain which would mean a running a 10 tooth sprocket (sort of small in the past we have been using 12s ) and I am a bit concerned that there would be more chance for the chain to skip.
although we stopped using chains three years ago in favor of spur gears, when we did use chains #25 always did the trick. we never had a failure in either drivetrain or arm design, although i have seen #25 break under periods of extreme stress, i.e. when lifting a heavy arm or supporting loads greater than 50lbs. good luck.
My electric scooter uses #25. We have always used #35 for our bots. I’ve heard that #25 can break under a lot of force. As for the size of sprockets, you need not worry with #35 chain. (we have used 10 t before) I can’t really say about #25 since I’ve never used it. As long as you have steel sprockets and the chain is tensioned properly, you should be okay.
McMaster.com lists the tensile strength of #25 chain as around 1000 lb. We use 1/4 pitch chain all the time with no problems. I’d guess you could go with larger #25 sprockets (thus reducing the chain tension) and still have a notable weight savings.
*Originally posted by Jim Meyer *
**McMaster.com lists the tensile strength of 25 chain as around 1000 lb. We use 1/4 pitch chain all the time with no problems. I’d guess you could go with larger 25 sprockets (thus reducing the chain tension) and still have a notable weight savings. **
The weight gain is beyond noticable. 3/8" chain is 4-5 times as heavy as 1/4" chain. You really limit yourself if you needlessly use heavier chain.
We’ve always used #35 chain, though we’re switching to #25 this year. After our all-steel bot last year, we’ve learned some things about weight. Switching to aluminum frame and #25 chain instead of steel frame and #35 chain should help in that regard. We basically discovered that our robots of the past were total overkill.
According to the Diamond Chain web site, 35 is 2.5 times heavier than 25. 35 is about .21 pounds per foot.
25 should be quite strong enough, but the connecting link is always the weakest. In addition, #35 sprockets are quite widely available, and very cheap. If you are using the larger bore sizes like 5/8, it’s a lot easier to find standard parts. Using aluminum #35 sprockets can offset some weight gains. Search the web on go-kart, Azusa and go-ped for various parts which may be adaptable. (Aftermarket Go-Ped wheels are awesome!)
We made the move to #35 chain this year from #25 in the past.
The drill motors we are using are approximately twice as strong as the ones used last year. There were teams last year that did indeed have some chains breaks with #25 chain. Our primary concern is the possibility of a wheel getting locked up for some reason and having the smaller chain break. Better safe than sorry.
We’ll just have to wait and see what happens this year.
We have used #25 chain for years, caculate the force:
Force = torgue/(PichDiameter/2)
Using the stall torgue of the motor. The chain is rated to be operated at a force of (1,250 lbs/ChainPitch) per ANSI Specifications. This means the rating is 312 lbs. for #25. This is a coninous service rating with probably a 2.5 safety factor over what a new cahin can with stand.
If you use too small of a drive sprocket you might have not only have a very high chain force, but bearing problems also.
I personally don’t like average ratings given in catalogs. Use the real machine info and you will have reliability.
You can find this kind of useful info as well as a lot of good stuff in the Machinery’s Hand Book.
The only draw back to #25 chain is it may need to be tighned more often. Where #35 chain can usually be set and left alone.
Yep. You need to use good engineering practices and check the references, plus apply a bit of common sense. Look at the chain/sprocket sizes used on go-peds, mini-bikes and the like and the forces involved.
If you get out on the hairy edge, then you have to really engineer it. Take a look at this if you’re into the dynamics of chain: http://www.ustsubaki.com/section2.html Neat stuff!
I would suggest to stay with the #35 chain. In last years competition, we were knocked out of a semi final (were selected by another team) from snapping a chain in two. We also snapped another during testing phases, but blamed it on the drivetrain’s assembly. Although we did have suspicion of the sprockets flexing a bit, putting the chain out of alignment. But none the less, I suggest you stay with the bigger chain.
We have always gotten by with #25 chain but this year we have switched to #35 (though we have not used chain for our drive system since our rookie year).
The reason is basically, we are worried about skipping chain with vigorous interaction expected. It is overkill we know, but we have seen so many teams lose matches because they have thrown a chain that we decided it was an overdesign we were willing to live with.
Bottom line, #25 can work well if you can keep the chain tight, the sprockets in line, and competitors from poking your chain from the side. Even if you can do all these things, you will sleep better at night if you use #35 chain.
We used #40 chain because of local availability of sprockets for the 5/8" diameter shafts. In short lengths it’s not that much heavier. We don’t worry much about it breaking during competition.
well just to scare you i’ll tell you that my team snapped our #25 chain when ever we really needed it to work. We put a lot of power into our drive train. We pushed up on the goal so we had a robot that effectivly weighed 220 pounds. Then combine that with the drills in low on a gear down the chain popped consisitently. It was unfortunate because we were the strongest robot easily at our regional(despite us not knowing that because it always broke.) We’ll this year we’re getting back at small parts for never shipping those 3/8ths inch sprockets and chain by using MSC only. (they still haven’t come… WERE WAITING!)
Second this year on our arm we really need to use 3/8ths in chain for controlling it. Its 9 feet long fully exteneded and weighs quite a bit. With a moment of about 110 to 1 its pretty tough on the chain. normally it puts about 910 pounds of force on the chain but if the arm gets hit that could easily spike and break the chain.
Of course our silly drivetrain designers used the 3/8ths chain in the stupidest place(rotating our drive modules) with sprockets that are reverersed!!(so its about ummm… 8 times as fast as it should be). Hopefully tomorrow i can bug them into changing it… the 6 sprockets and 10 feet of chain easily could save us 5 pounds if they were in 1/4 inch.
so in conclusion… you probably could break your chain, but i wouldn’t worry… nobody else seems to have problems.
P.S. Anybody got a solution to a chain where the its half an offset llink off? (as in a quarter link off)
This is our 3rd year and we have always used #35 chain and sprockets for our drive-train because it basically within our capabilities to do so. This year we have some large 45 tth sprockets which are quite heavy. Does anyone have experience in cutting hole patterns in these? What size and pattern should one use to lighten them without weakening them severely? Is there some information available for performing such operations?:rolleyes:
*Originally posted by Ianworld *
**P.S. Anybody got a solution to a chain where the its half an offset llink off? (as in a quarter link off) **
The last couple of years, to tension our chain, our mechs have used pieces of Delrin strategically placed where the chain comes near a convenient mounting place.
We’ve always used 35, but we’re considering going to 25 this year. We have the necessary material, but we have 35 on the bot right now. It would save us some weight, so we’re thinking about it.
