22-01-2017 17:07

ollien

Re: pic: Team 2559, Normality Zero Robotics 2017 Drive Train

What made you choose the meccanums and clamping gearboxes? The durability of those gearboxes under defense gives me the heeby jeebies.

Certainly looks like nice, though. Are you going to paint the clamping gearboxes?

22-01-2017 17:26

Cothron Theiss

Re: pic: Team 2559, Normality Zero Robotics 2017 Drive Train

You've made some interesting design choices here. Do you mind explaining some of them? First off, I see no way to mount bumpers. I'm gonna assume you guys already know how you're gonna mount the bumpers, but I'll strongly urge you to go ahead and CAD them in already. Why the decision to use the plastic bearing blocks instead of the aluminum ones? also, why did you choose to put the WCP tensioning cam on the clamping gearbox and not the bearing block? From what I've seen, relying solely on the clamping force of the plastic bearing blocks to keep your wheels from moving is not advised. Also, why all the shaft collars at the ends of shafts and not use ThunderHex with a screw and washer to retain the shafts? Finally, can you shed some light on the gearing and belting ratios, and what led you to choose them?

So far, it looks good!

22-01-2017 18:10

ImMoMo

Re: pic: Team 2559, Normality Zero Robotics 2017 Drive Train

Thanks! It looks nice in CAD, but painting is always dependent on time..

We choose the mecanum wheels because we wanted to line up more efficiently during gear placement and feeder station retrieval.

The clamping gearboxes were chosen for simplicity.. we haven't done any other drive train aside from standard tank. and the clamping gearboxes looked simple enough to use.


1. We will most likely add bumper mounts on the drive rails... about every 8''-- CADing them in is probably a good idea.

2. Tensioner placement was arbitrary, I didn't think it would make too much of a difference. I figured it would be easier having the wheels set in a constant position on all sides. Most of my research involved designs with the WCP tensioner on the gearbox.

3. Familiarity w/ shaft collars, I didn't think of any other way. I'm not quite sure I understand your suggestion with the screw.

4. Our initial gear ratio is 14:70, then the pulley reduction is 1:2. With our 4'' wheels that gives us a speed of about 20ft/s.. Simply put.. speed.. To avoid defense while traversing the field we figured if we were going fast it would be easier to avoid. Although we have the option to switch out the initial gear reduction to a 13:70.

edit: the plastic gearboxes and blocks were in efforts to reduce weight for an easier climb.

22-01-2017 19:05

Cothron Theiss

Re: pic: Team 2559, Normality Zero Robotics 2017 Drive Train

The WCP cam acts both as a tensioner and a hard stop for the clamping bearing blocks. From what I've heard, if you don't have some sort of hard stop for the bearing blocks, they tend to slide a little bit under the full weight of a robot. I don't know if this is true for both the aluminum and the plastic versions, but the weight difference between the two is pretty small.
I'd suggest you check out Vex's Application Guide for West Coast Drives, specifically page 14. It shows how you can use a screw and washer tapped into the end of a hex shaft to hold the wheel and/or pulley on without a shaft collar. It's cheaper, lighter, and in my experience, a bit more secure.
I have no idea how you're getting a speed of 20ft/s with the setup in the picture you've provided. For one thing, the gears pictured look remarkably like they're 72t, not 70t. Not much of a difference, but I think you need to take another look at what ratios you're actually wanting to use.



Going purely off of what's pictured in the CAD render, your adjusted speed is somewhere around 30 ft/s. That's not a robot, that's a missile with wheels. Frankly, I'd get rid of the second reduction entirely. 14:72 gives you a really nice reduction and puts your adjusted speed right at 15ft/s. And if you chuck the second reduction, you can get rid of the clamping bearing blocks entirely and just run the wheels off the same shaft as the gear.

22-01-2017 20:10

ImMoMo

Re: pic: Team 2559, Normality Zero Robotics 2017 Drive Train

The CAD model pictures a 14T pinion and 70T driven.
I'm sorry, I seem to have recalled the second reduction incorrectly.. the pulley reduction is 4:3 as we have a 24T driving pulley and a 18T pulley on the wheel shaft.

We have been talking about the option of removing the second reduction, because frankly 20 ft/s won't always be optimal.

The method you described seems interesting, I look into it!

Thanks.