CIM Motor Direct Drive or Supporting Axle

[loganc10]

Good day,

Over Christmas break, I plan on building an automatic tennis ball thrower for my parents dogs. I have purchased two CIM 12V motors as the two spin wheels that will launch the ball.

It will be very close to this project here. Youtube Project

Here are snippings from the above video.




I'm finishing up my bachelors in electrical engineering in the spring, so the electrical side of the project I competent in. However, the mechanical components of the system I am slightly struggling with.

I ordered two 8mm set screw hubs that I planned to use to hook my wheels directly up to the CIM shafts. However, looking closer at the above design, I noticed that it uses some sort of axle that is supported on the other side of the wheel. Is something like this absolutely neccessary?

I am not 100% sure what type of wheels I will be using, I am debating either lawn mower wheels or cutting and layering circular sheets of plywood then bolting those to my hubs. Below is the lawn mower alternative,

I'm not sure how I would attach these to the hubs though.

Thanks,
Logan

[Ari423]

I would say it's not 100% necessary but very much recommended. You are going to be putting a significant amount of sideloading on those CIM shafts. If they aren't supported, they will likely bend. Also, even with some load on the motor from the wheel, the CIM will be spinning at a significant percent of its free speed. That means it's spinning really fast (multiple thousand RPM). When the wheels come in contact with the ball a few times, it will likely shred the coating off the ball and the tread off the wheels. You may want to add a gearbox between the CIM and the flywheels to slow them down and give them more torque to push out the ball.

[loganc10]

Thanks for your reply.

I recently found a wheel that can mount to the hub I purchased below..




One obvious solution to me would be CIM Shaft >> Hub >> Wheel
This obviously would not have the other side of the wheel supported.

The shaft of the CIM is 30.3 mm and the hub is 20.2 mm.
In order to have the opposite side of the wheel supported would I have to do something like,
CIM Shaft >> Hub >> Some type of extension/coupler >> Bearing attached to frame??

Thanks,
Logan

[Monochron]

Originally Posted by loganc10

Thanks for your reply.

I recently found a wheel that can mount to the hub I purchased below..

http://i.ebayimg.com/images/g/9PgAAO...rwG/s-l500.jpg

This is kind of unrelated to the other conversations here, but I thought I would offer my own suggestion against using this type of set screw hub. I have had to deal with getting these to fit just right and keeping the setscrew from backing out and it is a pain. Especially with your CIM at 5000+ RPM I think this is going to be a headache for you.

I would recommend using this coupler on your CIM shaft to make it so you can use any wheel with a Hex bore. Then you could use tons of different wheels as long as they have that Hex hole in the middle. You would also be able to use this hub to connect to wheels without the hex hole in the midle.

It's totally up to you (and I know you already sunk money into that hub), but I just hate trying to use set screw hubs on a keyed shaft.

[asid61]

Originally Posted by Monochron

This is kind of unrelated to the other conversations here, but I thought I would offer my own suggestion against using this type of set screw hub. I have had to deal with getting these to fit just right and keeping the setscrew from backing out and it is a pain. Especially with your CIM at 5000+ RPM I think this is going to be a headache for you.

I would recommend using this coupler on your CIM shaft to make it so you can use any wheel with a Hex bore. Then you could use tons of different wheels as long as they have that Hex hole in the middle. You would also be able to use this hub to connect to wheels without the hex hole in the midle.

It's totally up to you (and I know you already sunk money into that hub), but I just hate trying to use set screw hubs on a keyed shaft.

We did set screws on our 2012 shooter robot, and the way the set screws go onto the keyed area makes it so that the wheels rotate with the shaft. We also have a 2-sprocket reduction before the output wheels, which are attache with set screws. I think it really depends on how hard you go on it, and what tip the set screw has.

[jwfoss]

You might want to consider going with something like the SpinBox from AndyMark and doing a single spinning axle/wheel with a hood.

[Monochron]

Originally Posted by asid61

We did set screws on our 2012 shooter robot, and the way the set screws go onto the keyed area makes it so that the wheels rotate with the shaft. We also have a 2-sprocket reduction before the output wheels, which are attache with set screws. I think it really depends on how hard you go on it, and what tip the set screw has.

Yeah, assuming the set screw is the right size to fit snugly in the keyway, it isn't quite as bad. In my experience the set screw was slightly too small and the walls of the keyway beat it up a bit.
Either way, even red locktite couldn't keep that thing from slowly backing out after an hour or two, and I think his application would require something long lasting. I'm thinking that an ungeared CIM like he is planning would make this problem much worse, but that's purely anecdotal.

[asid61]

Originally Posted by Monochron

Yeah, assuming the set screw is the right size to fit snugly in the keyway, it isn't quite as bad. In my experience the set screw was slightly too small and the walls of the keyway beat it up a bit.
Either way, even red locktite couldn't keep that thing from slowly backing out after an hour or two, and I think his application would require something long lasting. I'm thinking that an ungeared CIM like he is planning would make this problem much worse, but that's purely anecdotal.

Ours is slightly too large and ends up sitting on top of the keyway, actually. That combined with a soft steel shaft might account for the good seating, not to mention the accumulated grime holding it in.

[Joe Derrick]

Tennis Ball shooter Project from our AP physics Class

[jman4747]

You would be far better off supporting the shaft at the other end. You may also want to look at robot designs from the 2012 FRC competitions. Andymark.com has hubs like what you show that have 1/2", 3/8, 1/4" and other bores. Thus you can do, CIM Shaft >> 8mm Hub >> weel>> 3/8" hub >> 3/8" shaft >> Bearing attached to frame. Also are you familiar with FIRST Robotics already?

[loganc10]

While I have heard of FIRST Robotics and the competitions and seen designs online, I have never participated myself.

My above comment was a best guess at how I would support the otherside, however I do not believe I was very clear in describing it.

I would attach the 8mm hub to the CIM shaft, this hub would attach to the wheel previously shown. After the hub I would attach a coupler to what is remaining of the CIM shaft, allowing an additional 8mm shaft to go through the middle of the wheel to a bearing that is mounted to the frame. Maybe something like this?



Or would I be better off getting another hub and put on the other side of the wheel, which then connects the additional shaft (though not connected to the CIM shaft) to the bearing/mounting block?

Thanks for all your help, this stuff is just a little over my head. I plan to continue to do research.

Edit:

GeeTwo, thank you for a technical break down.. I kind of figured the CIM's were a tad overkill, but it was what the referenced project used with good results so I went with them. However, it is important to note that his wheels were milled from solid MDF and were pretty heavy.

Ari, I do plan on fabricated the frame myself. At my dad's work he has access to steel tubing and plate stock, figure it wouldn't be a problem for him and I to go there and throw something together. I've been looking for an excuse to learn to weld anyways.

Jman, your suggestion was what I was considering and trying to spit out. At the beginning of this post and also the prior.

I am going to continue look into possible wheels, however I'm slightly under a budget so the the possibility of lawnmower or custom plywood was taking that into consideration. However, I am still up for suggestions regarding them.

Thanks!
Logan

[MrBasse]

The CIM shaft isn't that long to begin with, it will never make it through a wheel. A hub on both sides of the wheel would be the best way to do it without some extra engineering. I would look in to a wheel with some give to absorb the ball a little and grip it well. Since you seem to have found Andymark.com, take a look at their 8" pneumatic wheel.

Alternately you could do something like this. It would give you a reduction and would allow you to use a $5-10 wheel instead of a $40 wheel. The only downside is that the bearings in those wheels are horrific at any kind of speed over a walking pace when mounted on a cart (think terrifying vibration and 2nd degree burn heat [ask me how I know about the burns]).

[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

[Chris_Ely]

This is the shooter that my team made for the 2012 FRC game. (sorry for the big image)

The wheels are supported by one shaft, with the a belt from the motors and gearbox. You could place the motors and gearbox in between the two sets of wheels you have pictured, and use two belts; one to the upper wheel and one to the lower wheel. I would not recommend using the pneumatic wheels that were linked to above, as the valve causes the wheel to be unbalanced resulting in horrible vibration.

[jman4747]

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

You are right but in 2013 we made a full court Frisbee shooter by mounting a 8mm hub to a cim and a 8" Andymark pneumatic and it survives to this day after several hours of running time since 2013 (we didn't know better). You really shouldn't do it if you can avoid it however and this is such a case.

Beware of using the pneumatic wheel at high RPM. I still remember how that max RPM warning showed up on the Andymark product page midway through the 2013 season. The primary problem was balancing it. The inlet port for air needs to be offset buy something on the other side. Also if you want to save money it's a less optimal choice. I would think andymark 6" or 8" rubber treaded wheels would do fine here and cost less.

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