A friend of mine has bad arthritis in his wrists and cannot easily throw a tennis ball for his puppy to fetch. They both enjoy the game but the current models of tennis ball throwers aren't easy on his wrist and those that are aren't very effective. My goal was to build something he could easily fire but still get appreciable distance from.
Please keep safety in mind and don't sue me. This device can be dangerous. It involves powerful elastics being used to accelerate projectiles quickly. Never point this at a living creature or valuables. Don't load this with anything that will intentionally cause damage. Don't combine any of the previous warnings to make a super destructive device. Seriously, you'll put an eye out.
On a lighter note this will exercise a dog because it launches tennis balls approximately 100ft as shown in the video.
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Step 1: Design
The design was a toss up between one with exposed bungee cords and a 2x4 for a frame and one with bungee cords contained in PVC which simultaneously acted as the frame. Since safety is always important the version which kept the bungees contained was chosen.
These were sketches I drew to present to my friend. He was impressed by both.
Step 2: Materials
Everything in this build can be found at hardware stores or home improvement stores.
1 @ 10ft length of 2" PVC pipe.
2 @ 48" heavy duty bungee cord
1 @ 48" 1-1/2" PVC pipe. Schedule 40. (2" can be used but is unwieldy)
1 @ 1-1/2" PVC cap 2 @ 2" PVC 90° elbows 2 @ 2" PVC 90° straight couplers
4 @ 1-1/4" metal pulleys
1 @ 48" 5/16-18 threaded rod
4 @ 3" 5/16-18 fully threaded bolts. (Carriage bolts will work in a pinch)
8 @ 5/16-18 acorn nuts
10 @ 5/16-18 hex nuts
12 @ 5/16-18 washers
1-1/2" x 5/8" corner brace
1 @ 5" flat angle brace
1 @ 6" flat angle brace with 3 holes per leg
1yard of 1" wide nylon webbing
1yard of 2" wide nylon webbing
Sewing machine thread
Thick string or thin rope
8" piece of scrap 2x4
8" 1-1/8" wooden dowel
3 @ #6 3/4" wood screws
16gauge galvanized steel wire
Spray paint that adheres to plastic
Step 3: Cut Trigger Mechanism
A band saw was used to cut the shape of the trigger mechanism shown here. An eight inch segment of 2x4 is ripped (cut parallel to the wood grain) laterally with a raised end. The raised end will eventually be used to hold the tennis ball hammock back. It releases similarly to a crossbow. This shape could also be cut with a coping saw.
A radial arm saw was used to rip a groove down the center of the shape. This channel will hold the trigger.
Step 4: Drill Trigger Mechanism
Drill a 5/16" hole in the crux of the smaller flat corner brace. This will act as a hinge when a 5/16" threaded rod passes through it.
The smaller corner brace will act as the trigger and the release mechanism. It must be placed so that it extends over the back of the 2x4. Mark a spot where the freshly drilled hole in the corner brace rests. This hole must be close enough to the top that the corner brace can sit in the bottom of the groove or the groove will have to be deepened by another pass on the saw.
Drill a 5/16" hole all the way through the 2x4.
To allow the corner brace to pass through the trigger mechanism a 1-1/16" hole must be drilled. Be sure to center this hole on the new 5/16" hole in the 2x4.
Once these holes are drilled the corner brace should be able to sit loosely in the trigger mechanism and a bolt should be able to pass through the 5/16" holes. When this is assembled the angle brace should be able to move back and forth.
Step 5: Refine the Trigger Mechanism
Since the tennis ball hammock will be pulled over the metal trigger it is important that it be free of burrs and sharp edges.
The corner of the angle brace should be rounded. A grinder and belt sander worked well. In a pinch someone could smooth this corner by rubbing it on concrete or using a metal rasp.
Step 6: Cut PVC
Cut two 30inch segments of the 2" PVC pipes. The PVC shown in some of these pictures is 1-1/2" which was used in the first try but 2" PVC is necessary.
These pipes can be cut on a band saw, table saw, radial arm saw or hack saw. It is vital to keep them the same length, preferably within 1/16" of each other.
Step 7: Drill PVC for Bolts and Threaded Rods
5/16" holes are drilled 1" from each end. The holes run parallel to one another. Each hole passes all the way through the center of the PVC and out the other side. Bolts and threaded rod must be able to pass cleanly through each of the holes.
Step 8: Drill PVC for Pulleys
The holes made in the previous step will fix the pulleys in place, the holes in this step allow the bungee to pass from the inside of the PVC to the outside where they can propel a tennis ball.
To reiterate: many of these pictures used 1-1/2" PVC but 2" should be used.
Hang a pulley from a bolt going through one of the 5/16" holes.
Mark out where the pulley touches the PVC. Mark above and below this area so that when the PVC is drilled from this area the pulley can hang freely.
Make 3/4" holes which will remove the PVC from the extends of this area.
Use a hacksaw blade to cut away the PVC between the holes.
A handheld jigsaw could be used to cut out the shape of this area.
Step 9: Refine the Pulley Holes
Smooth the holes using sandpaper or ideally a rotary tool with a sanding drum. Be wary of the dust. PVC dust is not toxic but breathing it is no fun and it is prone to static cling so it stick to everything causing a mess. Put a running vacuum nozzle in the end of the PVC to reduce some of the dust while you work.
The first holes made were not close enough to the 5/16" hole and had to be extended. The bungee would not pass freely through the hole.
After perfecting the hole in the first PVC pipe, mirror that hole on the the second pipe.
Only two of these oblong holes are made. That is one oblong hole per piece of PVC
Step 10: Sew Up the Tennis Ball Hammock
The tennis ball hammock is the nylon webbing configured to hold the tennis ball while it is flung out of the launcher. There is no metal on this part since it will be moving very fast and heavy metal could cause greater injury while nylon at this speed should not cause more than a welt. Even then someone would have to put their hand into the launcher while it is being triggered.
Two strips of 1" wide nylon webbing are cut. The 1" wide webbing is blue in this example.
The ends should be fused by waving a flame near the ends so they melt.
The ends of the webbing are sewn perpendicular to one another. When completed they form a bottomless cup.
A piece of the 2" wide webbing (black in this example) is cut long enough that it goes halfway around the circumference of the tennis ball. The ends of the 2" wide nylon webbing should also be fused with a flame.
A 12" length of 1" wide nylon webbing is cut and flame fused.
Loops are sewn into the ends of this strap. The loops must be large enough to accommodate the bungee cord.
This long loop is sewn onto the hammock so the corners of the "cup" come up to the loops.
This hammock will hold the tennis ball and the loop will go over the back of the trigger release mechanism.
Step 11: Modify and Install the Bungee Cords
The bungee cords used in this example are heavy duty. Regular duty may be used for a less powerful launcher. These cords had one fixed hook and one adjustable hook. A bungee with two hooks can be substituted without issue.
Remove the steel wires from the adjustable ends of the bungee cords. If the bungee only has two hooks remove one hook from each cord.
Cover the loose ends with tape to keep them intact. Using flame to fuse the ends of the bungee will fuse the nylon but also burn the rubber inside. This will smell awful so tape is preferable.
The remaining hook should be looped over the front end of the PVC. The front end has the oblong hole cut for the pulley.
The bungee will pass through both pulleys. The first pulley is allowed to freely hang inside the PVC. The second pulley is mounted with a 5/16-18 bolt to the outside near the oblong hole.
Push the hookless ends of the bungee cords through the loops of the tennis ball hammock.
Bend the ends of the bungee cord over.
Cut two 6" lengths of galvanized steel wire.
Use pliers to wrap a piece wire securely around the folded end of each bungee cord.
Pull the rear pulley down, this will take a little strength, and ensure the bungee inside is running parallel to itself. In other words, be sure it is not twisted.
Temporarily place a bolt or threaded rod through the hole to secure the pulley in place.
Do this for both pieces of PVC.
The launcher can now be given a preliminary test since just to ensure both sides can be pulled back.
Step 12: Modifying the Large Flat Corner Brace
The large corner brace was chosen because it has three holes on each leg. What is needed is two straight braces with an odd number of holes. All the readily available straight braces had an even number of holes which would mean more work than cutting up the neat angle brace.
Each leg was cut off using a horizontal band saw. A hack saw could be used for this step.
The pieces were ground down on an angle grinder. A metal rasp or cement could be used for this step.
The pieces were polished on a belt sander.
The holes were all drilled out to 5/16".
Step 13: Make the Front Bracket
The new straight braces can be attached to the same bolts being used to hold the front pulleys.
The 48" 5/16-18 threaded rod is cut into three pieces 16" long.
The cut ends should be smoothed.
Grind or use a flat metal file to round the ends.
If possible, use a belt sander to polish the ends.
Select the two rods closest in length to one another.
Put 2 of the 5/16-18 hex nuts near each end of one of those rods. They should be put an inch or more from the end.
Put one threaded rod through the straight braces so the braces rest on the nuts. This will be the top cross member.
Tighten two of the acorn nuts to the ends of the threaded rod.
Tighten up the hex nuts to the brace. This will secure the top brace.
Step 14: Install the Central PVC Pipe
The 1-1/2" PVC pipe holes the front bracket in place and keep the triggering mechanism parallel to the rest of the launcher.
Determine the length of the central pipe by aligning one end at the base of the trigger and the other end to where the bottom threaded rod will go in the front.
Cut the PVC to length
Align the front bracket and determine where the threaded rod should pass through the pipe.*
Drill a 5/16" hole for the bottom threaded rod to pass through.
Put a threaded rod through the new hole.
Put two washers on both sides of the threaded rod so they rest against the central PVC pipe.
Center the pipe as accurately as possible.
Tighten 5/16-18 hex nuts around the PVC and washers.
Put a 5/16-18 hex nut 1" or more from each end of that threaded rod.
Install the threaded rod as the bottom rod in the front bracket but putting it through the last holes of the straight braces.
At the end of the central PVC pipe where it touches the trigger mechanism six holes will be drilled. Three are pilot holes where wood screws will go through the pipe into the 2x4 trigger mechanism. The other three are larger holes where a long screwdriver can pass through to tighten the screws.
Make identical pilot holes in the 2x4 trigger mechanism.
Screw three wood screws into the pilot holes so they firmly connect the central PVC pipe to the 2x4 trigger mechanism.
At this point the launcher can be given a real test firing. Pull the tennis ball hammock down and around the back of the trigger mechanism. It should rest on top of the metal angle brace. Put a tennis ball in the hammock. Aim away from people and valuables and be wearing of ricochet. Pull the angle brace back like a trigger.
*I made this mistake of not angling the bracket when I first cut this pipe so I will give instructions later about how to modify this pipe so the launcher can be cocked using a foot rather than hands.
Step 15: Window Dressing. Aesthetic Upgrades. Improved Loading and Launching
If you plan to make this the most amazing launcher possible you may skip this step and keep working.
At this point a usable tennis ball launcher has been constructed. It's not pretty but it should be functional. The rest of the steps will make the launcher more appealing and give it a more finished look. Some of the steps also make it easier to launch and easier to load.
One of the greatest compliments someone can get as a builder is to hear someone ask, "Where do you get that?" The reason is that the questioner can't tell the difference between what you're holding and a finished product from the store. When someone asks "Did you make that yourself?" it's a high compliment but the questioner is also acknowledging that it is clearly homemade.
Step 16: Install a Corner Brace
The small corner braces are used to mount a handle right behind the trigger. The trigger must be mounted back far enough that it won't interfere with the trigger. Short wood screws are included if you buy a corner brace kit, often the only option, and I used some of the screws in a previous step to mount the central PVC pipe to the trigger mechanism.
Place the corner brace at the back of the 2x4 trigger mechanism.
Mark holes for the screws
Drill pilot holes.
Install wood screws so the corner brace is sturdy.
Make sure the wood screws are not so long they interfere with the operation of the trigger.
If the screws are too long cut or grind off the tip until they are short enough.
Install the corner brace.
Step 17: Build and Install a Handle
These pictures were taken after a paint job but they appear earlier since a handle is more critical to the function of the launcher than paint.
A 1-1/8" dowel is cut to 8" long.
The top is cut at a 45° angle.
A groove, the thickness and length of the corner brace, is cut.*
Be careful to not make the wood too thin at any point or the handle will be flimsy.
Holes are marked on the back of the handle where the screws should be installed.
3/32" pilot holes are drilled all the way through the handle perpendicular to the groove.
1/4" holes are drilled from the back of the handle to the groove.
Screws are tightened into the pilot holes securing the handle.
If necessary, cut a thin wooden biscuit to go above the handle and provide support. Glue this in place.
Wrap the handle in friction tape.
*An smarter method would have been to bend the corner brace 45° so the wooden dowel could simply be screwed in place. I recommend the bending method.
Step 18: Make a Rear Guard
The rear guard allows the launcher to rest on its bottom. This also protects the trigger mechanism from harm and accidental triggering. If safety isn't enough to convince you to perform this step then consider that the launcher can be loaded by foot if the rear guard is installed.
Ideally, the 2" PVC pipes with the bungee would have been made 4" longer so there would be no need for the small lengths of PVC and straight couplers. I recommend this method.
Cut two lengths of 2" PVC to 4" each. They need to be identical.
Place the straight coupler on one of a 4" segment.
Place the 90° elbow on the other end of the segment.
Do this for both segments.
Lightly push the straight couplers onto the rear of the launcher.
Measure the length of PVC needed to connect the two elbows. Don't forget to include the length needed to go inside the elbow, not just the gap between the elbows.
Cut an appropriate length of PVC.
Snug everything together. Solvent welding is not necessary.
Step 19: Angle the Front Bracket So It Can Be Loaded by Foot
As mentioned earlier, the front bracket should be mounted at an angle so a shoe can fit between the tennis ball hammock and the bracket. This is accomplished by (measuring twice the first time *ahem*) drilling a new hole in the central PVC pipe which is closer to the trigger mechanism. If the rear guard is not installed, there is little point in modifying the angle of the front bracket.
Remove the central PVC pipe from the threaded rod.
Reinstall the threaded rod without the central PVC pipe.
Loosen the nuts on the bolts which hold the pulleys.
The front bracket will now rotate easily.
Find and angle where a shoe can fit between the bracket and the tennis ball hammock but the tennis ball can still exit the launcher.
Hold this angle by hand-tightening the nuts on the pulley bolts.
Make a mark on the central PVC pipe where the threaded rod touches.
Pilot a hole at this mark.
Finish the hole by drilling a 5/16" hole all the way through the PVC.
Reinstall the central PVC pipe the same way as before. The front bracket will keep this angle and allow for easier loading.
Step 20: Paint
There are better instructions for spray painting than I will give here. This example uses two colors for the launcher. The central PVC pipe is green while the 2" PVC pipes are soft blue. In places where the blue didn't cover well it looks like clouds in a blue sky. That's what I tell myself.
The PVC was separated from the rest of the hardware.
If possible, sand off the text from the PVC.
Protect your surface from paint by resting it inside a box or on some newspaper. A painting booth would be ideal.
Wear gloves to keep from getting messy hands.
Apply paint evenly.
Dry overnight. It's possible to overturn a chair and use the chair legs as a makeshift drying rack. The chair legs will get a little paint on them.
Step 21: Shamless Self Advertising
This build took me roughly a month. It is not based on any plans other than what I mentioned in the first step so there was a lot, a LOT, of troubleshooting and part replacement that isn't mentioned here. I'm proud of it. Very proud.
I run a blog where I talk about all kinds of things I build, including an unabridged version of this project where I talk about all the things I did wrong as well as what I did right. There are other neat things there like a device that lets you hear temperatures and a keyboard you can use from inside your pockets.
Runner Up in the
Outdoor Workshop Contest
Second Prize in the
Launch It! Contest
Participated in the
Summer #mikehacks Contest