pic: 3 CIM WCD Ball Shifter CAD

[Bryce2471]

Originally Posted by Chris is me

The CIM mounting is especially concerning as the moment applied by the mass of the motor will tend to bend the pinions away from the cluster gear, weakening both of them.

There's no reason to lighten a gearbox so aggressively when you have all that extra material in your gears that serves so much less function than the material you've removed from the gearbox.

I don't see how the top motor is mounted less securely than the top motor of the WCP 3 CIM DS gearbox. In this design the plate is thinner, but the upper standoffs are closer to the CIM.

If I was going to lighten the gears, I would lighten them as much as reasonable too, but that is a different story.

[Jared]

I agree with others who say that the top CIM isn't mounted well enough. Your gearbox might survive, but adding that extra support for 0.05 lbs gives you a lot more gearbox strength. The heavy CIM motor hanging off the end of the plate will cause the plate to deform, especially when your robot accelerates/decelerates really quickly during a collision.

If you look at many teams' gearbox plates, you'll notice that the plate outlines tend to be completely convex, rather than having little things sticking out. The outline is entirely made up of straight segments, and segments of circles that have their centers inside of the outline of the plate. This also adds a ton of strength, and requires the same size stock to machine from.

The top one is mounted in a weaker configuration because of the orientation of the mounting screws.

[Bryce2471]

Originally Posted by Jared

If you look at many teams' gearbox plates, you'll notice that the plate outlines tend to be completely convex, rather than having little things sticking out. The outline is entirely made up of straight segments, and segments of circles that have their centers inside of the outline of the plate. This also adds a ton of strength, and requires the same size stock to machine from.

I've looked at these gearbox designs before, and I wasn't able to see how it benefited the strength of the gearbox at all. If you could be more specific about how that improves the gearbox strength, that would be really helpful.

The top one is mounted in a weaker configuration because of the orientation of the mounting screws.

As far as I can tell, the top CIM on the WCP 3 CIM DS gearbox is mounted in the same configuration.

[Jared]

Originally Posted by Bryce2471

I've looked at these gearbox designs before, and I wasn't able to see how it benefited the strength of the gearbox at all. If you could be more specific about how that improves the gearbox strength, that would be really helpful.

Imagine trying to twist off the little round parts that the standoff screws go through with a pair of pliers on your gearbox design, then imagine trying to do the same thing but with a 0.15" thick outline around the entire plate, so it's a convex shape. Right now, it's like a little tab that can twist off without causing the rest of the plate to deform, but if you had the convex shape, you'd have to push a lot harder and make much more of the plate deform before you break off the mount. It also makes the gearbox more rigid and ties everything back to the standoffs.

As far as I can tell, the top CIM on the WCP 3 CIM DS gearbox is mounted in the same configuration.

On the lower two CIMs, it appears that the mounting screws are close to vertical. When gravity tries to pull down the end of the CIM motor, it tries to pull the upper mounting screw out of the CIM.

On the upper CIM, your mounting screws are horizontal. Instead of trying to pull out the screw, gravity will deform the gearbox plate and swing the motor down. Last year, I did a simple stress analysis on a couple of our gearbox plates in SolidWorks that were really revealing with motor placement/plate design. I'll see if I can post some screenshots from those to show you what I'm talking about.