pic: Stackerbox Mecanum Prototype

[JesseK]

Originally Posted by s_forbes

Also note that the kit bot has an aluminum bracket bolted to an aluminum frame; lots of frictional force! Lexan may not act the same way and might slip, but I don't know for sure. A turnbuckle may be a very good idea! (or one of those cam shaped tensioners, like on the 968/254/60 drive)

A steel washer could be put in between the lexan face plate and the frame to create the same frictional force.

Now that I think about it, an aluminum or thick plastic cam as a locking mechanism could be useful once the chains are tensioned and the four transmission bolts are tightened. This may be the simplest and most lightweight option. Cam design is also an area of CAD I haven't explored yet.

Originally Posted by Water Bandit23

This might be a stupid question, but what type of metal is the frame made out of?

As shown & calculated it is 6061 T6 Aluminum. This reminds me, I need to make some adjustments and figure out how the cyllindrical plate spacers can be welded in such a cramped area...any ideas?

Originally Posted by gblake

Also, to avoid having the chain tension creating a moment that wants to twist the shaft the drive sprocket is on, a bracket that wraps around the sprocket and supports both ends of the shafts could be what is at each end of a tensioning system.

Blake

For the design I'm not worried about a moment on the output shaft, since such a force is usually the result of overtensioned chains or misaligned sprockets. I'd also like to note that the output shaft is already supported in 2 places by bearings and adding a third support is generally asking for too much complexity. A locking or permanent tensioning mechanism (as you suggested) combined with good build practices should circumvent this concern.

Originally Posted by AdamHeard

I usually wouldn't use a COTS turnbuckle to tension chain as it just seems big and unweildy..... But, if you got one that is about the length between the inner bolts (to the center of the robot) on one stackerbox and the inner on the other, and the eyelets were about the clearance size for a #10, you could tension both chain runs by pulling the gearboxes towards each other.

This seems like a great idea, but 1885's recent bad experience with tensioning systems that are dependent upon each other has put a bad taste in my mouth.

EDIT: on second thought, get a turnbuckle with plain threaded ends instead. Make a block with a threaded hole for that end on one face, and a clearance hole for a #10 on the perpendicular face (not vertical). Put that block on one of the inner #10s on each of the stackerboxes, and hook up the turnbuckle to them.

If implemented independently, this is probably the best way to deal with tensioning to make it zero-maintenance. I'll experiment with the cam system described above and this one for revision 2.

Thanks for the feedback guys, keep it coming!

[colin340]

i woul just move the stacker boxs cloeser to the wheel and go with a all gear drive Tran

[Not2B]

Originally Posted by squirrel

or even just a channel across each end, so the frame can flex, since mecanums like "suspension".

That is an important thing to remember. A little frame flex is a good thing for mecanums. Makes a big difference - at least it did on our '08 robot.

[AdamHeard]

Originally Posted by colin340

i woul just move the stacker boxs cloeser to the wheel and go with a all gear drive Tran

In this case having chain as the final reduction is a good idea; provides a method of changing the final gear ratio without moving the gearboxes, also the frame can flex/bend slightly and still run.