Is this shooter design sound?
 

Is this shooter design considered to be sound? I'm pretty amateur at this, but I wanted to know if this design would be considered to be sturdy enough on a competition robot. The idea of the design is that their will be two modules spinning on both sides (not pictured) and will act as both the intake and the shooter. The wheels are positioned so that the center of the colsons is over the center of the boulder. I'm especially worried that since the mincim is direct driving the wheels, it will put side-load on the motor, that was part of the rationale for putting a bearing.

Yes, I do realize that there are alternatives to this design, such as using a 1:1 versaplanetary base with a cim adapter just like the Ri3D greenhorns.

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Re: Is this shooter design sound?
 

You could make this much simpler with a Versaplantary and some L 2x2 versaframe.

It looks fine but is not going to be easy to manufacture with limited tooling (Something I assume you have) and is definitely more prone to failure.

It looks to me like a greenhorns style shooter. We have done something similar and have CAD for it. You can either contact Gingerpower on here (One of the members of RI3D greenhorns) or if you just want a few basic dimensions and pics of CAD me.

Re: Is this shooter design sound?
 

Thanks for the reply,

I agree with your sentiment, using a versaplanetary would guarantee no sideload on the motor and would make gearing down trivial; however, the 4x2 colsons have already been bought and I don't know how they would fit onto the output shaft of the versaplanetary. So I would need to order the hex coupler regardless. With the hex coupler taking up that much space, a versaplanetary approach might end up using just as much vertical space as this design.

Re: Is this shooter design sound?
 

How we attach 4"x2" colsons (they're on our current shooter prototype) is to put the wheel all the way onto the output shaft and then retain it on the shaft with a 1/4-20 screw into the threaded hole at the front of the shaft and a washer to make sure there's contact with the face of the wheel. Throw some blue loctite on the thread before you put the final bot together and that connection will hold through the competition season.

That being said, the output shaft on a versaplanetary isn't particularly rigid when it comes to side loads farther out on the axle, meaning it might be worth it to come up it a solution to strengthen the output shaft a bit. I've got my own ideas, to be sure.

Re: Is this shooter design sound?
 

There's definitely been a lot of good suggestions in this thread. I like the fact that you're taking an existing design and incorporating it into your robot, but I love the fact that you're going to make it better. That's exactly why we do Ri3D.

If you have any questions about our design just PM me! I will say that using a versa planetary as a shaft adapter worked nicely for us, and we had no problems with it.

Re: Is this shooter design sound?
 

So, first off i'd like to apologize for the random cross-hatching going on in my attached image.

Here's another solution on supporting a shooter wheel to be direct driven by a MiniCIM, as well as a breakdown on the factors that were considered when this was designed.

I'll be referencing this image.

First, note that we decided to support the wheel from both sides of the shaft. The bushings inside of a CIM and miniCIM are NOT designed for axial or radial loads, and will cause early failure of the motor if they're subjected to too much force.

Second, our method of clamping the hex shaft onto the CIM shaft is based off of available hardware, as well as keeping it mechanically simple. We're not driving the robot with this wheel, so a split hex with a collar is good enough, especially when a bit of keystock is thrown in the mix.

Finally, the whole system was designed to keep the CIM away from the forces imparted into the shooter when the boulder is released, while maintaining as much speed as possible. Since there's only a single shot allowed at a time, we weren't concerned with creating a heavy flywheel to maintain wheel speed post-shot. What we wound up with was a compact and fairly simple method of propelling a wheel.

The bits I'm not showing in this drawing involve shoving the ball very precisely into this wheel and a second exactly like it.

Re: Is this shooter design sound?
 

I'd consider that to be a decent design, however, I would be a lot more comfortable if you used two or three two inch standoffs to prevent bending in the plates. With the current design, the forces caused by shooting the ball (which are actually quite large, they cause considerable recoil in our shooter, even when someone is standing on it) will easily cause deformation in the plates.

Re: Is this shooter design sound?
 

The only CIM motor I have personally seen blown was when a flywheel was mounted directly to the output shaft. (FRC195 in 2013)

It seems you have somewhat accounted for this with the bearing after the motor. The only further analysis I would recommend is to see how you would like a VersaPlanetary 1:1 output here. It is likely a little bit heavier, but would allow very easy mounting and easy motor replacement if neccessary

Re: Is this shooter design sound?
 

Firstly, I'd like to re-emphasize what was said earlier about standoffs, so the plates are held at a constant distance apart and aren't flexing independently of each other. Additionally, I would make sure that all your bearings are supported all around them, because from the image, it looks like the bottom bearing might be a bit close to the edge (I can't be sure, it just looks that way).

Anyway, here's a little bit of food for thought, to toss around before you lock in your final design.
Have you prototyped this setup? Have you done the math/experiments to show that the shooter is able to intake balls as well as shoot them? I would be concerned with getting the required torque for intake and also the high RPM's required for shooting, but it doesn't mean it won't work, just that if I were you I would want proof that it will work before I spend a lot of resources on it. Is there a plan for keeping the ball in the robot/shooter without contacting the wheels once it has been picked up, so that the wheels can spin up to speed before you launch the ball?

I hope this gets you thinking about design more critically. The concept you designed is definitely a neat idea, and certainly one that could work, as long as the specifics are done right.

Re: Is this shooter design sound?
 

I would be careful using shaft collars to hold the assembly on the hex shaft. Our team has found that they are unreliable and fall off. As an alternative I would drill a hole and use a pin.

Re: Is this shooter design sound?
 

This design doesn't reduce any sideloading on the CIM shaft. Bearings only provide significant radial support forces that you can rely on. You're still using the bushings in the CIM for support.

Now, if you're really concerned about sideloads (I wouldn't be, but I don't know your specific applications), I'd support the wheel on either side with a bearing (like in a typical FRC drivetrain), then couple the wheel to the CIM with one of these that allows for shaft misalignment: http://www.mcmaster.com/#standard-sh...lings/=10un04v

That way you don't have fighting with misalignment, which would add friction that both reduces max speed, rev up time, and longevity of your device.

Re: Is this shooter design sound?
 

I think you'll find that many teams are successfully using shaft collars to retain things on shafts. We have been using them for a couple years without any issues or slips. As long as you have everything assembled properly I think they are reliable.

Re: Is this shooter design sound?
 

In your picture, you show a hex coupler. I've had a terrible time trying to find a 1/2" hex coupler. Do you have a source for one? We have limited tools and machining one is probably out of the question.

Re: Is this shooter design sound?
 

Vex sells one: http://www.vexrobotics.com/217-4008.html Super useful for both prototyping and building.

Re: Is this shooter design sound?
 

I would strongly advocate (depending on your packaging and size constraints) mounting the wheel in its own pair of bearing and driving the colson with a 1:1 timing belt. Not only does this prevent side load on the CIM it stabilizes a wheel that will be spinning at a relatively high RPM and allow for future ratio adjustments.