Mecanum on kop chassis

[Underdog_19]

One of our mentors calculated the speed of the 6.7:1 gearbox to be around 19 ft/s. Seems really fast. I wonder why AndyMark went with this setup.

[zbross]

Originally Posted by TerryS

Andy Mark just released this 6" Mecanum upgrade kit for the AM14U2. IMHO, the 6.7:1 gearbox ratio is too low for this years game.

http://www.andymark.com/product-p/am-14u2-Mk6.htm

For anyone planning on using this upgrade kit (as we are) and find that it is already out of stock, I just heard back from AM that it was listed as Out of Stock when it was first posted by mistake on 1/13. It will be listed as In Stock when the 6" HD Mecanum wheels come in, expected on 1/16. The other parts are in stock and can be ordered now and separately as listed.

[Ether]

Originally Posted by Underdog_19

One of our mentors calculated the speed of the 6.7:1 gearbox to be around 19 ft/s.

I'd like to see that calculation. Could you ask him(her) to post it please?

[s_forbes]

Originally Posted by Ether

I'd like to see that calculation. Could you ask him(her) to post it please?

I get roughly the same:

(5300 rot. motor / 1 minute) x (12 rot. idle shaft / 28 rot. motor) x (14 rot. wheel / 40 rot. idle shaft) x (6*pi inches / rot. wheel) x (1 ft / 12 inches) x (1 minute / 60 sec) = 20.8 ft/sec

That's under the assumption that you're moving straight forward/backward and the mecanum rollers aren't contributing to sideways motion. Also ignoring frictional losses in the transmission. In reality I'd expect it to go a bit slower than that, but it still seems to be off by about a factor of 2 for this years game.

[Ether]

Originally Posted by s_forbes

I get roughly the same...20.8 ft/sec

I get 20.749 fps vehicle speed at 5310 rpm CIM speed for 6.7:1 gearbox with 6" dia wheels.

What I was asking about is the 19 fps.

[hhoover]

Does anyone really expect to get 5300 RPM from CIMs on a loaded robot? I would expect (from the current limits) that 3000 is pretty close to the upper limit.

None the less, I concur with s_forbes that it's still way fast for this years tasks where precise positioning will be a boon.

[s_forbes]

Originally Posted by hhoover

Does anyone really expect to get 5300 RPM from CIMs on a loaded robot? I would expect (from the current limits) that 3000 is pretty close to the upper limit.

I would think 80-90% of the CIM freespeed rpm to be a reasonable expectation for an FRC drivetrain. Regardless of that, this transmission looks like it's geared way too high. We'll likely be taking our chances with the toughbox nanos instead, though we'll have to add a bunch of ugly holes to the chassis.

[asid61]

Originally Posted by hhoover

Does anyone really expect to get 5300 RPM from CIMs on a loaded robot? I would expect (from the current limits) that 3000 is pretty close to the upper limit.

None the less, I concur with s_forbes that it's still way fast for this years tasks where precise positioning will be a boon.

The max speed is the speed when the cims are at 5300rpm in an ideal world. In reality, some speed is lost to external influences (generally, I use 80% ideal for my calcs, but it varies). The mentor who calculated 19fps may have used a smaller loss constant.
3000rpm seems pretty low even for a relatively low-tolerance robot, but I could be wrong.

[Mike Marandola]

Originally Posted by Sperkowsky

Nope

This is wrong. Why wouldn't you be able to? Special mounting will be required though.