#25 Chain Drive Experience ???

[akoscielski3]

With everyone saying its not the stretching but its the sprockets. Is there anyway to stop that? Would making steel sprickets be beneficial and still save weight?
We are thinking of switching but I gotta make sure before I use them. We will most likely use them on our prototype drive train this year.

[Nick Lawrence]

During my time on 1503, we ran #35 chain in the drivetrain. While #25 is plenty strong enough, the biggest concern was sprocket allignment. Rather than spend hours machining spacers to 0.0005" tolerances, we felt our "quality" maching time could be better used for the parts that really needed it.

Personally, I'd rather spend the extra time and run #25 chain all around. The weight savings is huge.

-Nick

[JamesCH95]

We generally use #25 for mechanisms and #35 for the drive-train.

According to AM #35 chain is .25lb/ft and #25 is .10lb/ft. In a drive train that used 16ft of chain (average for us I think) #25 series would save 2.4lbs vs #35.

This weight difference could be reduced by using smaller sprockets and no tensioner with #35 chain. We've used half-links to tension our #35 chain drives during initial assembly, never touched them after that, and never thrown a chain in the 3 years I've been coaching.

[Brandon Holley]

Originally Posted by Nick Lawrence

Rather than spend hours machining spacers to 0.0005" tolerances, we felt our "quality" maching time could be better used for the parts that really needed it.

Personally, I'd rather spend the extra time and run #25 chain all around. The weight savings is huge.

In my 12 years, I've run #25 chain on 9 robots (1 other was #35, 2 others were belts) and never threw a chain. You definitely don't need 0.0005" tolerances to get the alignment right. What you do need is careful design, and a little love at final assembly to ensure everything fits as designed.

I understand the "bullet-proof persona" that comes along with #35 chain, but I think any team is capable of using #25 if they want to. It just comes down to taking the time and effort in areas where you usually may move fast. Theres no need to machine spacers of +/- 0.001" of each other when you can buy shim stock and punch out spacers in whatever size you may need.

I know our final assembly of our drives with chains was carefully done over a couple days to ensure everything fit as intended. This is at the point where all of the pieces of the drive are DONE: machined, polished, cleaned, anodized. It's often tempting to rush and throw every piece together in an hour. I think our track record shows taking your time at this step is time well spent.


One reason we actually switched to belts was to make assembly a bit faster, which absolutely did decrease the time required at that step.

-Brando

[Chris is me]

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.

[IndySam]

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.

[Aren_Hill]

Originally Posted by IndySam

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.

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