Hello, first time posting here.

I am trying to make what will in the long run be an automatic ball launcher for a dog. I am fairly experienced with embedded systems so I'm not worried at all about the software side of the project.

The method I'm going for is to have two spinning wheels that the ball gets launched from between. So first order of business is to get two wheels, two motors, and mount them up to see if it will at least launch a ball! This is where I am stuck. I'm pretty sure a DC motor is the way to go because I just need something that spins relatively fast and has enough torque to launch a ball when it makes contact. I'm not sure how to determine what specs I need for the motors. High enough RPM, but also high enough torque. I'm also not trying to break the bank..

Here are some of the motors I have been looking at:
https://www.digikey.com/product-detail/en/nmb-technologies-corporation/SE24P2CTCE/P121383-ND/6021450
https://www.digikey.com/product-detail/en/nmb-technologies-corporation/SE30R2NTCD/P121384-ND/6021451
https://www.digikey.com/product-detail/en/crouzet/82740402/966-1741-ND/3190266

The first one seems pretty good for $12, but the second one has more torque..

Am I at least on the right track here? Are there any better websites than DigiKey for this type of component?

Thank you!

 

I can't see those small motors performing that function.
The first is under 1amp!
Try a autowrecker for more powerful 12vdc motors.
Max.

 

Ahh, I see. I'm not sure what you mean by "autowrecker", but I'll look around for higher amperage then. Digikey seems to be lacking in that department (for anything less than around $70, that is).

A quick search on ebay yields these options:

https://www.ebay.com/itm/Genuine-MA...706843&hash=item21176a0d82:g:FPMAAOSw3utY5kYf
https://www.ebay.com/itm/12v-DC-motors/352199947218?hash=item5200c0b3d2:g:6KIAAOSwfjRZ-2RR
https://www.ebay.com/itm/100-W-24-1...121973?hash=item2388b078b5:g:6e8AAOSwv~1aLAtP
https://www.ebay.com/itm/NEW-12V-DC...419761?hash=item3af6f5fe71:g:mowAAOSwuYVWn1kf

Are these in the right ballpark?

 

You have to find out or get an idea what torque is required to operate the mechanism first.
Auto wrecker is a automotive scrap yard, source of 12vdc motors.
Max.

 

I think autowrecker should mean a crazy driver!

I think I'd start by thinking about the initial velocity of the ball. I would assume your spinning wheels should have the same tangential velocity at the "pinch" point. That and wheel diameters will allow you to calculate the RPM. Then the question becomes how much force will be needed to pull the ball through the pinch point. At this point experimentation will be needed, I think.

There are various projects to do what you want.For example - http://www.instructables.com/id/How-To-Make-a-Ball-Launcher/ At least, they might help you understand some of the principles.

But this is my favorite one by far

 

So first order of business is to get two wheels, two motors, and mount them up to see if it will at least launch a ball! This is where I am stuck.

Usually the method is to build the mechanics and then find out empirically if possible. the required torque required before purchasing the motors.
Max.

 

A way to get around the need for a beefy motor is to use flywheels, or just make sure your spinning wheels have plenty of mass so they don't slow down too much when the ball hits them.

 

I would use a pneumatic tube instead. It would be a lot easier to make the launcher anyway. The problem would be with loading the balls automatically.

 

But this is my favorite one by far

This is great! That dog is so cute. You can see he really loves that thing. Makes me want to go out and get a dog so I can build one of these things.

It does beg the question of why dogs love to chase balls?

 

Could it be done with a solenoid? One could abuse with higher currents for short durations.....if the repetition is not too fast.

 

It does beg the question of why dogs love to chase balls?

It is built in to their recessive memory, they are distant descendants of the wild dog, but there are some things that cannot be erased.
See the classic example in the utube video Fenton in Regents Park.
Max.

 

I've seen one built with a motor about 1 or 2 HP belt driving a wheel/tire on the frame of an old utility (boat?) trailer. I don't recall the detail he used but another tire/wheel rested on/was driven by the other and the balls passed between. He said he basically copied a baseball pitching machine.

 

Could it be done with a solenoid? One could abuse with higher currents for short durations.....if the repetition is not too fast.

I like it.

(Mod note: Thank you for pointing out that this was leading to a forbidden topic)

 

• Perhaps you should drive both wheels using a single motor with a belt and pulley connecting them. It occurs to me that if one wheel is going a little bit faster than the other it might not shoot the balls in a straight line.

Scooter motors can usually be picked up fairly cheap on ebay. They're usually available in 12, 24, 36 and 48V versions with power ratings up to around 500 W. I expect that would be adequate for what you're doing.

 

Rather than use two wheels I think I'd try a single spinning disc having a fence along a diameter. Drop the ball on to the disc centre and centrifugal force would throw the ball off the disc edge at a tangent. A fixed fence near the circumference could constrain the path of the ball.