***NOTE: I get occasional requests for detailed measurements. All the information you need is in the Sketchup file on this page. Look for the link to "Pitcher 2016-04-13.skp". You will need the freeware Sketchup program, and once you open it, you can use the measuring tape (shortcut key: T). Thanks. ***
Here are the plans for a small pitching machine I built to help my son practice batting for Little League. It reliably throws the ball at a set rate in a set direction. I do not know the top speed it can attain. It very easily throws balls the distance from the pitcher's mound to the home plate in a rather flat arc. It is designed to allow adjustment in several dimensions so as to change the arc shape and speed of throw.
First, a word of caution. This is, in effect, a catapult. Things will fly out of it at painful velocities. The arm will whip around with mighty force, easily capable of breaking skin and bruising, perhaps breaking bones. Faulty materials or workmanship on this spring- loaded device could produce an explosion of wooden and metal shrapnel. Eyes could be lost. This is not to be used by children. Rather, it is to be used by adults playing with children. Build and use at your own risk! I give no promises as to its safety or fitness for any particular purpose.
Second, you'll need the free software Sketchup to open the plans above.
Though the build looks complex, it's really just a few 2x4s, bolts, a spring, 2 hinges and 2 ball bearings. Total cost was less than $25.
Step 1: Hardware and Plans
Download the Sketchup plans here and take a look. If you are new to Sketchup, you'll want to find the tape measure tool (press "t") to get the dimensions as you cut your boards. Everything was made from 2x4 pine ($2.08 for 8' at Home Depot).
Other hardware you'll need:
- Spring. This one looked about right, so I bought it. You can overthink these things.
- Eye bolts x 2. I always use 5/16" bolts for everything, so I never have to wonder if I have matching nuts, wingnuts, ball bearing sets, etc.
- Ball bearing sets x 2. Inner diameter is 8mm, I think. Got me a bunch on Amazon years back and keep using them for various projects.
- Hinges x2. Used a 3.5" door hinge for the foot tensioner and a strap hinge for the release.
- A mess load of 5/16" bolts, nuts, and wingnuts. Just go to the aisle for fastener hardware and buy 10 of each length bolt from 1" to 9" if they have it that long. It'll last you a dozen projects, and you'll have to interrupt a project to go back to the hardware store less often.
- A 12" threaded rod, as always, 5/16" diameter. This will be the axle for the throwing arm.
Step 2: Assembly
Once you have your parts cut out of 2x4, you'll need to drill holes for attachments. I always recommend Forstner bits and a drill press for countersinking nuts.
When it comes to the throwing arm, you will need to countersink the ball bearing sets on both sides of the arm, and drill a hole through the arm *larger* than the 5/16" axle so that there is no contact between the wood of the arm and the axle.
Using a router table, a groove was cut in the arm to guide the ball.
Step 3: Putting It All Together, Firing
As you can see from looking closely to the images above, there are multiple points of adjustment to get the throw you desire.
- The ball rests against a bolt on pitching arm, allowing you to position the ball. More distance to run down the track means higher speed, to an extent-- if it doesn't make it to the release ramp by a certain angle, the throw will be weak.
- Ramp on arm can be moved up and down. Biggest effect is on release angle.
- Multiple holes in the tensioner arm (the foot pedal) allow variation in spring tension
- Multiple holes in release arm allow different range of arm motion, affecting spring tension and time until release. This is limited, though, as any cocking beyond parallel to the ground causes the ball to roll off the arm.
Testing at the ball field revealed a problem with the front end rising as the pitcher throws, leading to undue variance in velocity. A sandbag or other weight on the front should both remove this variance and increase power (less energy diverted into moving the pitcher itself.
If you like this project, please vote for it in the "Make it Move" contest on Instructables. Thanks!