Designing a clay disk launcher

ksukhin

I began designing a clay disk launcher for when I go to a gun range and I want it to be something like this:
http://www.youtube.com/watch?v=8KVK8svZzbI

I am having trouble sizing an electric motor since I don't have much exposure to E.Eng.
The clay pigeon launcher is about 10cm by 10cm and I calculated my exit speed to be 20-35m/s if it's going in a projectile motion (min X distance = 30m & min Y distance = 10m)

RPM = 20 m/s *(60s/min) * (rev / ∏(.1m)) = 3820 RPM
RPM = 35 m/s *(60s/min) * (rev / ∏(.1m)) = 6685 RPM

If I plan on using a 1:10 ratio of clay pigeon to driver I'd need a 1m dia. wheel going at 382-668.5RPM. This is where I run into issues....

1) Is that possible with an electric motor?
2) How do I account for rolling friction?
3) How do I calculate the max RPM for the clay disk before it shatters?

Travis_King

That seems like an awfully big wheel...what's your reasoning behind the 1:10 ratio?

ksukhin

I'm not sure if I can get an electric motor powerful enough to make the wheel spin at the required rpm if I reduce the radio.

I'd like to have it powered by a portable battery that you use to boost cars. But then again I run into the issue of finding out if the motor/battery are powerful enough and how long it will last

Travis_King

You should take a look at your calcs, your rpm requirements are based on the pigeon, not the throwing wheel. Of course, you'd have to factor for motor slowdown when the pigeon enters the system as well as losses due to slip, but the rpm requirement should be based on the throwing wheel, not the pigeon, as the exit velocity will depend on the tip speed of the wheel.

Even a 30cm wheel reduces your requirements considerably. You should have no trouble finding motors that run at this speed, though they might get costly depending on your requirements.

check out this website: here

ksukhin

How do I use the exit speed to calculate the HP output I would need then?

berkeman

A big part of engineering is optimization. Often you optimize your performance/price point, or you try to find a good tradeoff in vehicle performance versus fuel mileage, etc. So it's important to be able to step back from a design periodically, and ask yourself if you are doing the best that you can in your design to optomize it.

And sometimes you will see that the way you are trying to do something is inferior to other design options for one reason or another. That's when you should ask yourself if there is a better way to accomplish your overall design goals.

In this case of yours, think about the inefficiency of keeping a motor running the whole time between bird launches. All of that is wasted energy, which will force you to use a larger battery than you want, and/or will limit the usefulness of the launcher because it cannot run for very long on one charge. Using a spinning disk might be okay if you have AC Mains electric power available, but not many ranges have electrical outlets at the launcher location (which is why you are thinking of battery power).

Can I ask why you want to do this instead of just building a traditional spring-powered launcher? They are very simple and efficient in their design, and since they are human-powered, no other power sources are needed. If you just want to build a different kind of launcher, then you need to consider the efficiencies and optimization issues more, IMO.

To save on battery power, you could have an electric motor that pulls back the spring-loaded launcher arm, for example. Then you are only using up battery power for the couple of seconds that it takes to arm the launcher. You can use a simple motor with a screw drive to pull the arm back, and a couple solenoids for engaging/disengaging the screw drive, and for releasing the launch. You can even get fancy and make an auto-loader for the birds, so you don't have to have anybody at the launcher for a set of shots. And then add in some mechanism that lets the launcher change its aim on its own, and you can have fun all by yourself at the range....

ksukhin

I feel like using a spring is clunky especially if they begin to rust after being exposed to rain and other things. I was thinking of using a portable generator with like 3000-4000W but I still don't know how to size a motor based on my speed requirementsand battery output. Plus if I reduce the size of the big wheel, doesn't that meant that it would have to spin faster in order to produce the right exit speed for the pigeon?

billblack

Do_All White Wing Automatic Trap.
Battery operated.
Works every time. No engineering required.
I have built claybird throwers in the past. If you have a machine shop and a lot of time, it is an interesting enterprise.
If you actually want to shoot instead of tinkering with the machine I heartily recommend this:http://www.cheaperthandirt.net/produ...QixnQodG04AUg#
At the very least go to a trap, skeet or sporting clays field and do some research on prior work...what is already being done in the field. There really isn't much to the overall concept. The devil is in the details-like throwing fairly fragile things at 60+ mph without breakage.
Good luck. If you pursue this, please post pictures of your progress.

berkeman

How does it work? Is the battery power used to pull back a spring arm?

ksukhin

I believe you are correct.....I also believe that I made a mistake calculating my RPM for the disk. My exit speed has to be 20-35m/s but that is linear, I think what I found was ω. Essentially how fast does the 1m wheel have to spin in order to be the equivalent of 20-35 m/s

I want to know what RPM the clay pigeon disk will reach as it's accelerated to 34m/s

Can anyone help me do this calc?

berkeman

The circumference of the disk is 2*Pi*R. So the linear speed of the outer edge of the spinning disk is 2*Pi*R*(number of revolutions per second). If R is in meters, then the answer is in units of m/s.

But, that is not the linear speed of a disk launched by such a rotating disk, unless the bird has no spin (which would not make for a very stable flight). How are you meaning to launch your clay bird with this spinning disk?

berkeman

BTW, I didn't watch the YouTube video in your original post (OP) -- maybe that would answer my question. I'm at work, and don't watch YouTube videos from here...

ksukhin

When you get a chance watch the video. The people in it did it exactly they way I want to do it but with a freebie and I think a bike wheel

ksukhin

So I am stiff having issues figuring out the size of my motor. I have attached my calculations below. My numbers end up being ridiculously high and at this point I'm not sure what I'm doing wrong.

1) I want to find the RPM that the clay disk develops as it is accelerated to 34 m/s. At 4) I get it to be 6500 RPM, which seems unusually high.

2) The acceleration ends up being 14720 m/s^2 based on my circumference distance that the clay disk has to travel to reach 34 m/s. Also my time to do that is .001 sec

3) I calculated my driving wheel torque to be 2.3 ft-lb, now is there a portable motor that will be able to provide that kind of torque?

Attached Thumbnails

   

pantaz

That's a Frisbee launcher. I sincerely doubt a fragile clay pigeon can survive such a mechanism.

Every clay thrower I've seen uses an arm. The rotational speed of the clay is fairly low -- again, I doubt one could survive the kind of RPMs you're specifying.