Quote:
Originally Posted by madz
Thanks, guys.
We have it set up where we can't run two separate chains off the same axle because our robot is almost too wide with no good ways to save any more room, so they have to be in a line. We are using overlapping 6-inch wheels.
We designed it with idler gears so that all the sprockets should have half or more of their teeth on the chain if we use one long chain. But one question is how often do chains break? Ours in on the inside and protected from hits, and the axles are supported on both ends so we hope nothing will bend.
Or if we drive two wheels with one motor and one wheel with the other motor, will that cause problems driving and turning? One end of the robot is heavier than the other by design so we thought putting the one wheel drive on that end. It drove fine with the 2-motor-3-wheel tank gear train and no drop center.
We can test these things later this week, ourselves, but want to make sure we aren't doing anything too silly.
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Our FTC team (3507 Robotheosis) avoids using Tetrix gears anymore if we can avoid them, or only for prototyping purposes. Tetrix axles bend too easily, the framing system is too flexible, and the motor mounts are too imprecise for keeping a pair of gears properly spaced and aligned as robots get used, abused and banged up while competing.
Chain drive designs tolerate greater assembly imprecision and abuse, but they do put more stress on the axles/bearings. Note the stiffer overlapping channel mini bearing modules in the PICS below (1st two from prior years). We also never torque the driven items via the axles - we just attach driven sprockets to driven item and let axles free spin in bearing blocks. Note also the use of long heat treated 10-32 socket head cap screws as axles. With just a bit of polishing of the unthreaded zone they make terrific and very rugged high performance axles.
Our chained drive train this year sounds similar to yours, but with eight 6-inch "wheels" having two overlapping pairs per side pattern, with a single motor for each pair.
A previous year's design:
However for your chain runs, I strongly advise you to to NOT use the Tetrix set screw motor hubs (not even with a pair of them per sprocket), because of the set screw loosing issue with the frequency of reciprocating high torque that a drive train demands.
Get the new 2-piece Tetrix clamping motor hub from from and make sure to lube the set screw with just a tiny bit of grease so you do not get any on the bore hole. They will stay tight much better than a set screw hub and they better handle the frequent reversing torque that a drive train generates.
With six wheels and four motors, any weight imbalance (front/back) from having the longer/heavier chain of the two wheels paired with the one motor on each side will serve to help climb the mountain if it is toward the front. Our front-to-back weight split point is located just behind our 2nd (from front) wheel axle, which helps enormously for climbing the churros.
-Dick Ledford