Re: #25 Chain Drive Experience ???
 

Honestly, in our experience (a short run in a gearbox and a short run for a big arm), alignment was important but not absolutely critical or anything. I mean, for teams without a lathe that use the Kitbot and extruded parts, 25 might be a challenge, but if you have any reasonable manufacturing capability it's more than doable.

Re: #25 Chain Drive Experience ???
 

Generally chain "stretching" is every little join on every link wearing.
The reason you see more stretch on #25 is not because it is weaker but is because you have more links per inch to wear down.

Re: #25 Chain Drive Experience ???
 

It is also partially attributed to the lubrication slowly working its way out of each pin joint.

Re: #25 Chain Drive Experience ???
 

Tom

Did you order extras? I have been working with small teams so we have been ordering just enough + 1 spare so when both sprockets come in with notches in them, we are stuck. I will consider different sources in the future but the steel ones from Grainger get pretty heavy when the tooth count gets high. Does anyone have any suggestions for sources of better quality #25 sprockets other than AM?


Nick and Rob

It was great to see your most eleagant robot in the flesh in St. Louis and to be able to speak to some of your students. It was one of our favorites this year. I think your school is just a few km of where we used to live in TO. See you next time.



Phil

Re: #25 Chain Drive Experience ???
 

AM is the only person in the market that sells sprockets in #25 in aluminum. Maybe some other supplier might, WCP will in the distant future :p

But for now, you could send them back? We've called AM a few times for random misc. problems, they've been so kind to ship out replacements ASAP.

Instead of buying them you could router/laser/waterjet them from .118 or .125 plate and then chamfer them yourself? Do you have access to a CNC machine or do you have sponsors that own them?

-RC

Re: #25 Chain Drive Experience ???
 

In my experience, even #25 chain can be run fairly misaligned under some circumstances. Last year, we ran our practice bot with one sprocket on backwards. Their was not much load (it was an intake being powered), and the misalignment was fairly substantial, approximately 1/4" over about a 4" run. When we realized that it had accidentally been installed incorrectly, it had been running that way for almost a week with no problems.

I'm sure that high tension, high load drive chains are much more given to throwing with misalignment, but don't get scared away from a lighter solution. To add one more story to the others in this thread, we've run #25 drive chains for at least 4 years with absolutely no problems with misalignment. We did experience a bit of stretch, but our tensioners have solved that problem very handily.

Re: #25 Chain Drive Experience ???
 

#25 chain at 5k RPM in general sounds scary. We had to massage our sprocket sizes for our intake to ensure that we would not exceed the rated surface speed of #25 chain and that was substantially slower than a shooter wheel.

Re: #25 Chain Drive Experience ???
 

We've done it on a prototype. It was a little scary bit it worked.

Re: #25 Chain Drive Experience ???
 

In our shooter, our surface speed probably topped 4000 surface feet per minute. We geared up the output of a CIM through chain, which gave us an output RPM of about 7500. It never threw a chain, but it made a noise like the starship enterprise booting up.

For an even more crazy number, our belts (which were what actually touched the ball) had a speed of about 5890 surface feet per minute. That's almost 70 miles per hour. The saddest part: we could barely even make shots from the key.

Re: #25 Chain Drive Experience ???
 

That's got me wondering: what's the failure mode of #25 chain at these speeds? How is that surface ft/min rating established?

Re: #25 Chain Drive Experience ???
 

Agreed. As soon as we started talking about speeds of 4k+ RPM, we completely eliminated chain as an option.


Tristan- I'd also be very interested in that answer.

-Brando

Re: #25 Chain Drive Experience ???
 

My concern with exchanging the sprockets is that it would just be a waste of time. Since both sprockets had the same "notch" in them, this is indicative of the design or the CNC programming of the sprocket so any replacements would also likely have the same flaw.

Unfortunately, we do not have access to a CNC nor do we currently have sponsors who can make one available to us.

What alternative power transmission method is recommended at these high speeds? Belts? Gears?

Thanks.

Phil

Re: #25 Chain Drive Experience ???
 

Could you post a picture of what you're talking about? An error on two sprockets doesn't necessarily mean the whole production line is ruined - and I'm sure if you sent AndyMark a picture they would let you know if your replacement would have the same defect.

Re: #25 Chain Drive Experience ???
 

Unfortunately not. Once we saw how the notches affected how the chain seated on the sprockets, we filed the notches out so that we could get on with testing. We neglected to take photos so the evidence is gone now. Also, I am working with another team this year since we moved across town. Driving over 40-60 minutes one way was not fun.

I did some hunting around and found some aluminum sprockets with hubs made by Berg. These use set screw hubs and "pin hubs" so it may be best to broach a keyway in them.

www.wmberg.com/catalog/catpage.aspx?url=pdf/B05A107.pdf


I also found some glass reinforced nylon sprockets made by Torque Transmission.

torquetrans.com/roller-chain-sprockets/index.htm


I will give their distributors a call and see what their stock looks like.

Re: #25 Chain Drive Experience ???
 

Hi Rob

Where do you buy the thicker AL #25 sprockets ?

Re the Dark soul tool ( http://www.team221.com/viewproduct.php?id=70 ) I had no idea that it got rid of the masterlink. Thanks

Dave