How to attach wooden flywheel to DC motor.

Thread Starter

GoatJames

Joined Aug 8, 2020
5
What's the best way of attaching a wooden (plywood) flywheel to the shaft of a DC motor? The flywheel is relatively small (4 inches in diameter). I'm still deciding on the motor, but the diameter of the motor shaft will probably be somewhere around 5/16 inch.

I was thinking of just drilling a hole in the flywheel and using some sort of glue, but I want to make sure that when the flywheel is attached to the motor, the spin is flat (no precession), stable, and durable, especially for my high RPM application. I was also considering using a propeller adaptor designed for RC drones so that I wouldn't have to attach anything to the motor shaft permanently, but then I need to figure out how to attach the wheel to the prop adaptor.

What do you guys think? Have you done anything similar in your projects? Any suggestions are welcome. Thanks!
 

MaxHeadRoom

Joined Jul 18, 2013
21,257
One ideal way is a metal or plastic boss of some kind with a flange to mount the disc to.
The bore would conform to the motor shaft dia.
Max.
 

Thread Starter

GoatJames

Joined Aug 8, 2020
5
One ideal way is a metal or plastic boss of some kind with a flange to mount the disc to.
The bore would conform to the motor shaft dia.
Max.
It seems that most bosses that I can find online are threaded, but I would prefer to work with DC motors with circular shafts (no threading, no screw holes).
 

jpanhalt

Joined Jan 18, 2008
10,103
A hole in the center of the plywood will not hold for long. Get a propeller adapter at virtually any hobby shop that sells airplanes or online:

1596931729661.png

The collet end goes on the motor shaft. The wood flywheel is clamped between the nut, a washer, and the flange. If you need more area, get a "fender washer" and use that between the nut and wood. The flange is usually serrated so you will not need anything additional on the back.

Propellers on engines of 1 HP or more are held by a single nut and front washer.
 

BobTPH

Joined Jun 5, 2013
2,505
Or a wheel hub intended for the motor shaft. Look on robotics sites. I used one of these to spin a Barbie doll for a prop I made.

Bob
 

Tonyr1084

Joined Sep 24, 2015
4,918
high RPM application
Define "High RPM" please. I've seen CD disks fly apart under extreme RPM, and they're no where near as unbalanced as a piece of plywood with a hole cut somewhere close to the middle. My first thought is that this could fly apart and injure someone. Have you ever been hit with flying wood? I have. A table saw kicked back a 3/4 inch thick 12 x 12 piece of plywood right into my gut. Left a hell of a bruise. That's why there's safety devices on them. Flying wood can be dangerous.
A hole in the center of the plywood will not hold for long. Get a propeller adapter at virtually any hobby shop that sells airplanes or online:

View attachment 214313

The collet end goes on the motor shaft. The wood flywheel is clamped between the nut, a washer, and the flange. If you need more area, get a "fender washer" and use that between the nut and wood. The flange is usually serrated so you will not need anything additional on the back.

Propellers on engines of 1 HP or more are held by a single nut and front washer.
I really have to double down on this suggestion. I think it's a great idea. But I'm still concerned about the balance and durability of plywood as a flywheel. Even a 4 inch wheel can spin dangerously fast if it comes apart. Could also ruin your motor if it's not highly balanced. I'm wondering how you're going to achieve that. Also, wanting to know (just to reiterate) what do you call "High RPM"?
 

djsfantasi

Joined Apr 11, 2010
6,719
Balancing a plywood disk could be difficult and take a lot of work. There could be voids in one of the layers which would affect balance.

You could make a balancing jig of two single edge razor blades and use a temporary axle. Rotate the disk a few times and mark it on the bottom where it stops. Then sand off some of the plywood near the marks and repeat. Continue for a mind numbing number of times, until where it stops appears to be random.

However, if your adapter is not almost perfectly aligned with the temporary axle, all this work will be for naught.
 

jpanhalt

Joined Jan 18, 2008
10,103
Yes, wood is not very homogeneous. However some grades of plywood are much better than others. "Aircraft" plywood (available in hobby shops) is usually birch or some other hardwood and does not have voids. Marine grades may also meet that criterion.
 

MaxHeadRoom

Joined Jul 18, 2013
21,257
May pay to look at some other materials, For such as this, I visit the local plastics wholesaler, off-cuts are to be had fairly cheap.
Max.
 

Thread Starter

GoatJames

Joined Aug 8, 2020
5
Define "High RPM" please. I've seen CD disks fly apart under extreme RPM, and they're no where near as unbalanced as a piece of plywood with a hole cut somewhere close to the middle. My first thought is that this could fly apart and injure someone.
My project is launching ping pong balls at medium velocities with a double flywheel system, similar to flywheel NERF guns. (very similar to the idea presented in this thread: https://forum.allaboutcircuits.com/threads/counter-rotating-wheels-for-shooting-pingpong-balls-and-motor-speed-controller.39556/). It appears someone has had success with a 5000 RPM motor, so that is around the range I will be targeting.

The material of the wheel isn't set in stone, so thanks for the tip. I will consider other materials for the wheel to increase safety. The actual composition of the wheel isn't super important to my project - I plan on adding some sort of rubber foam on the circumference of the flywheel to add crush (better grip = more force) to the ping pong ball. Plywood just happens to be cheap and easily shapeable.
 

Thread Starter

GoatJames

Joined Aug 8, 2020
5
Thanks for all the suggestions everyone! You've given me a lot to think about and a lot of leads to investigate - I'm glad that there seems to be multiple ways of approaching this problem.

I will update as soon as I make progress on the project.
 

MisterBill2

Joined Jan 23, 2018
6,745
One suitable choice could be roller-blade wheels, which are very strong and they have a surface that would grab the balls very well. You would possibly need to put a bit of glue into the bearings to increase the torque, but you may not need to do that. The big plus is that they come with well centered bearings in place, and so they could just slide onto the shaft if it was the correct diameter. And if not, then machining an adapter sleeve is not that hard.
 

Bernard

Joined Aug 7, 2008
5,619
AH- a ping pong ball pitcher, I still have mine. The motors came with a short removeable linear actuator screw shaft held by 2 set screws. Motor shaft maybe about 3/16", ACME screw about .3".
Because of small shaft size ball bearings were used on far ends. That is why I suggested 5/16" minimum single ended shaft size. The problem is finding a small motor with a big shaft. The wheels are of standard grade 3/4" 7 ply wood with a band of closed cell foam tape about 1/4"thick- & still in good condition.
 
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MisterBill2

Joined Jan 23, 2018
6,745
Roller blade wheels should be close to the right size at 3 1/2 inch diameter. And they are already very round with well centered bearings. And a surface perfect for driving ping-pong balls, or golf balls for the really Gonzo folks. Producing round enough plywood disks just sounds quite challenging without a good lathe and a fair amount of skill.
 

Tonyr1084

Joined Sep 24, 2015
4,918
5000 RPM, 4 inch diameter - um - that's (4 x 3.1416 = )12.57" circumference. Traveling at 5000 RPM, that's (12.57 x 5000) 62,832 inches per minute. (1,047 per second) (3,769,920" per hour) or 60.64 MPH.

Now, if you're driving the PPB (Ping Pong Ball) with a single rotating wheel, holding the other side of the PPB with a stationary guide then it'll launch at 30.32 MPH. But if you're driving it with two wheels, then that's going to be at full speed.
 

MisterBill2

Joined Jan 23, 2018
6,745
I have seen how they do it with baseball pitching machines, quite similar except they use those small trailer tires and by running them at different speeds they can put quite a spin on the ball. It would want to be two wheels for a ping-pong bal launcher to avoid having an awful spin and a resulting serious curve. And while the roller blade wheels are smaller diameter they are also better able to grab the ball very consistently.
So is the TS building a practice-mate device or a weapon? Or just a really cool thing? It could be any one of these.
Are we next going to have a request for s citcuit to measure the spin speed??
 
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