Would it be a good idea to use the chains for the robot’s drive chain, spanning over 16-17 inches?
Kind of like this:
Of course. As long as your robot is legal in every other aspect, you should be fine. My FRC team uses 25 chain on our chassis, so I think you should be fine. 
As long as your group has some method of tensioning the chain, that should work just fine. It won’t work without tension though.
You have to also put into the picture that chain is less efficient than gears over a certain distance since chain has a 70% transfer of the original energy put out, and gears have a 90% rate of transfer of the energy produced. So gears over a certain distance would be more efficient than chain. But the 16-17 inches shouldn’t be to big of a deal.
Our team used to run the intake with chain, but then we encountered some problems with it slipping off the sprockets. We redesigned the intake to use gears and even though it was the same ratio the gear drive was faster and now our intake picks balls up ever faster!
I hope this helps
Andrew
Hmm… this is contrary to everything I’ve been taught, which is that a well-lubricated roller chain set up in proper alignment can be 98% efficient. Can you provide a citation for your 70% figure? I’m confused.
Sorry for the long response
I have heard everything from 70%-98% but it all depends on alignment as you said but a WPI college professor calculated 70% efficiency so i really don’t know. I personally had problems with chains in FTC with correct spacing and everything and would not trust it as a drive system.
I know it has nothing to do with the original question, but with that wide wheel spacing (front to back) it will make it difficult to turn your robot (not impossible, just difficult) since the wheels have to skid sideways a lot to turn.
This may be an issue since you also show a 1:3 gear ratio (speed up).
Don’t be surprized if your motors tend to stall while turning, thus consuming a LOT of battery power.
You robot will be very fast in a straight line, but turning may be a serious issue.
Phil…
You want to be REAL careful about not stalling those 12-volt motors. They overheat and die much faster than you would think, and we have a box of dead motors to demonstrate it.
Chain alignment is probably the most crucial operation you will have to perform with #25 chain, along with maintaining good chain tensioning. If the chain becomes slightly loose, and you take a side hit from another robot, it can walk the chain off the sprocket. Tensioners in the middle of a chain run can help substantially to minimize this potential. 17 inch wheel spacing is a dimension we have used with a single tensioner, and with good sprocket alignment, we have lost only one chain in 14 years of competition. That happened in the days BB (before bumpers), and the chain took a direct hit from another robot frame.
Hodge,
This is a FTC thread. The driving forces and speeds are a lot lower than with FRC motors.
In general, they should have no problem or need only a rudimentary chain tensioner.
Regards,
Mike