CIM Motor Direct Drive or Supporting Axle

[loganc10]

Originally Posted by akoscielski3

As a rule: never ever side load a motor. So you should not directly drive the wheel from the CIM Motor. You should add a set of gears/belts and pulleys/sprocket and chain to each wheel.

Does side loading a motor mean driving the wheel directly, supported or not? I was looking to stay away from a bunch of pulleys, gears, etc. The more of those the more mechanically inclined I need to be. While I believe I could pull it off, I'm not sure I want to deal with the headache and price increase of those extra components.

What tools do you have access to? That can change a lot of things.

I have access to basic power tools. No machine shop or anything extravagant like that. I'll be utilizing my dads work for some steel stock and welding equip. for the frame. But other than that I'm not looking to do any fancy fabricating.


What are your thoughts on THESE wheels? The downside of the rubber threaded wheels on AM is that they are only an inch or so wide, potentially requiring two (side by side) to attain the required width for a tennis ball. These Vex wheels come up to 2.5", however with a lower diameter.

Can anyone comment on the bearing and housing needed on the other side of the wheel that will attach to the frame? I'm not super familiar with them, and what exactly I need. Will something like in the photo above work?

Thanks,
Logan

[philso]

Originally Posted by akoscielski3

As a rule: never ever side load a motor. So you should not directly drive the wheel from the CIM Motor. You should add a set of gears/belts and pulleys/sprocket and chain to each wheel

Why to not side load the motor? You will likely destroy it. The bearings will not last as long, break and then your motor will burn out. You could also bend the shaft of it or something else can happen

In 2013, some of our team members made prototype frisbee shooter with the wheel driven directly off the motor shaft. After several shots where the compression (= side load) was set too high, the motor bearing at the back end failed.

[asid61]

You could use that, or just drill a hole in the side and stick a ball bearing in with some locktite. That might be cheaper, although using what you show above might work too.
I would also recommend making everything out of wood instead of metal, as it is cheaper and easier to work with.

[jman4747]

You will sacrifice speed with smaller diameter wheels and they don't have to be as wide as the ball. The ball just needs to hit the center of the wheel. Two side by side would give better accuracy but this application doesn't require it so a physical constant that keeps the ball mostly centered as it hits the wheel would be enough.

My suggestion would be to mount the 8mm hub to this wheel and on the other side use a 3/8" hub with this bearing at the end of the shaft.

If I were designing an FRC robot this assembly would be totally different but this application should't require it.

[GeeTwo]

From a mechanical standpoint, two CIMs is overkill unless you're planning to project a stream of balls. Unless your parents have 101 Dalmatians fetching those balls, you won't need this much power. If you make your wheel systems heavy enough (that is, with a sufficiently high moment of inertia), you can spin your wheel tips just a bit higher than the desired launch speed.

As ballistic range is simply v² sin²2θ / g where θ is the launch angle, to throw a ball 32 feet through the air, you only need a launch speed of 32 fps at a 45° elevation. For a CIM free spinning at 5310 rpm, that would be about a 1.4" diameter wheel. A 1000 rpm gearmotor on a 7" or 8" wheel would provide this same speed. Motors of this type have an 11Ω resistance when not turning (I have several handy, including one that actually lives here at my computer desk.) This implies a stall current of a bit over 1A. If you use one for each wheel, you're going to have about 6W of mechanical power assuming a nominal 50% efficiency at high speeds (50-80% of free). A tennis ball weighs 2.1 oz, so throwing it at 32fps requires mv²/2 = 2.1 ft-lb, or 2.84 J. At 12W mechanical power and even assuming another 50% loss due to friction, you could throw at least 1 ball per second.
For tread, I would definitely recommend something much softer than a lawn mower tire. AM solid rubber wheels would not be too bad, but blue textured nitrile would be even grippier, though it might need to be changed out every few months of dog play.
Pololu and other vendors sell decent 4mm D-shaft hubs, though getting this up to an 8" wheel might be a stretch.

I don't seriously recommend the 25m gear motor, but I wanted to point out that a pair of them was (at least theoretically) adequate to the task. A BAG motor or two with VP gearbox(es) and colsons is probably the easiest way to go with plenty of room for adjustment.

[Ari423]

Also, these look like custom side plates and base plates. Do you plan on making them yourself or do you have a plan to buy them somewhere?