Motorized Ping Pong Ball Guns

This Instructable will teach you how to make a motorized ping pong ball gun. These ping pong ball guns are a lot of fun to build, but more fun to shoot. I made this as a Christmas present for my son.

UV LED lights are mounted inside the gun to charge glow-in-the-dark ping pong balls for great night time shoot outs. The UV LEDs also add a cool glow to the barrel of the gun as well.

A red laser with a crosshair pattern is mounted on the front of the gun under the barrel.

The gun is powered by two packs of four "AA" batteries so you can use rechargeable batteries and stay green. One pack runs the motors that fire the ping pong balls. The other pack powers the flashlight head on the top front of the gun, the UV LEDs that charge up glow in the dark ping pong balls, and the laser on the bottom front of the gun.

This video shows the ping pong gun in action and then has a walk through of the gun components.

I think this type of project would be a great candidate for 3D printed parts or parts cut with a CNC or laser cutter. It would be great to have those options for this type of project. I think it would help a great deal with accuracy of the individual parts.

Materials and Tools Needed

A lot of the parts I used to build this were items that I already had or had left over from other projects. I recommend that you customize this or other projects to use up some of your existing materials. For me it's a great feeling to use up left over materials instead of storing them for years or throwing them away. Also, it saves you money and you make room for the next big project.

MATERIALS

Motor and Wheel Assemblies
I purchased my motor assemblies several years ago from a surplus site and then couldn't find them again. Recently I found more of what look like the exact same assembly at the surpluscenter.com web site for $4.00 each. Here is the link. They are listed as "3 VOLT DC 1000 RPM MOTOR PAIR". The ones I have were listed as 6 volts DC. I can not be sure these are the same as I don't have any to compare against the ones I used for this project.

UV LEDs - Technical Specifications

Wavelength/Color Emitted: UV/Purple (400-405nm)
Lens Color: Water Clear
View Angle: 25 Degrees
Forward Voltage: 3.0-3.8v
Current: 20mA
Size: 5mm
Luminosity: 7,000 mcd
Used 150 ohm resistors for 6 volt dc power

Other Materials

1/8 inch, 1/4 inch, and 1/2 inch thick baltic birch plywood
Wood Screws - mostly #4 and #8
20 gauge stranded electric wire for wiring
Pushbutton switch from Radio Shack - Catalog #: 275-009
Rolling lever switches from Radio Shack - Catalog #: 275-017
AA Battery Box from Radio Shack - Catalog #: 270-409
Machine screws
Metal Hinge
Aluminum spacers (for triggers) from Home Depot.
Glow in the dark paint for ping pong balls. - I decided to not use this paint on the ping pong balls and instead buy glow in the dark ping pong balls I found at KMart.
- Glow in the Dark ping pong balls from KMart
GOGO 3 Star 40mm Blank White Ping Pong Balls from Amazon
Aluminum multifunction LED flashlights

Tools

The tools I used on the project were as follows:

Table saw
Band saw
Oscillating spindle and belt sander
Cordless drill
Drill press
Scroll saw
Hacksaw or cutoff saw
Sanding block with sandpaper
Screwdrivers and wrenches
Soldering iron
Hot glue gun
Wire cutters
Multimeter

Not all of the tools in this list are required, but will make the construction much easier.

NOTE: If you plan on using any tool for a project please make sure you are familiar with the tool and all of the dangers associated with it. If you are not familiar with a tool then you should ask someone who is to show you the proper way to use it. A lot of communities have classes at local colleges on the proper use of tools and machinery. There are also local woodworking clubs that offer classes at very reasonable rates for beginners. I highly recommend using these resources for your safety and for the most efficient use of the tool.

SAFETY FIRST
Always wear eye and hearing protection.
Always work safe with the proper safety equipment and guards on your tools.

Sketch a Design and Put It in the Computer

The sketch of the design was really based on some different ideas I had for these ping pong guns. The design resolves around the motor and wheel assemblies I had. Basically I knew the gun had to have the motor assemblies attach to the sides of the barrel and the barrel of the gun had to be able to pass a ping pong ball through it.

I originally sketched up some designs on paper with what I thought the ping pong gun should look like. I decided to have the barrels be square instead of round to simplify the construction and thought it might look better anyway.

I designed the guns in Autocad as 3D items and then imported the model into 123D. I've been using autodesk products for a long time so this was the fastest way for me to create the 3D model. The different file types are attached for your use. I added materials to the objects in 123D and thought the rendering looked real good. The colors of the different parts of the gun were used to keep the different items separate and easier to see.

The Autocad DWG File and the 123D files are attached for your downloading if you like.

Downloads

PingPongGunFinal.123d

PingPongGunFinal.dwg

Plan Out the Materials

Like a lot of my projects I try to use left over material from previous projects. A lot of this gun uses 1/4" thick thick baltic birch plywood and a few thicker pieces. There are some other pieces I used, but that is the majority of the wood material. Baltic birch machines great and is very stable. It also rarely has voids like other plywood.

I already had the motor assemblies. I don't think these are available any more, but I think these could be easily reproduced using drive wheel rollers from a place like McMaster and dc motors.

The UV LEDs I used were ordered specifically for this project through a vendor on Ebay. I wanted to use UV LEDs for the inside of the gun to charge a glow in the dark ping pong balls. I thought these would look really cool at night and my kids would have a lot of fun with them.

I picked up the battery holders, switches, and resistors at Radio Shack.

Cut Out the Gun Body Pieces

The gun was designed to be opened up later if needed for maintenance. Because of this the assembly is relatively easy. It is mostly screws holding wood pieces together. I did add matching screws on the side of the gun that doesn't open so the sides would be somewhat uniform. I colored the screw heads black with permanent marker to have them blend in with the rest of the gun.

I cut most of the pieces for the guns out using a table saw and band saw. I sanded the edges of the pieces using an oscillating spindle and belt sander. Don't get too hung up on getting all of the pieces cut exact or having square edges. I think it's better to have the edges sanded slightly for a softer feel anyway.

Try to cut out bother side pieces of the gun at the same time. You can hold them together with double sided tape or leave a few tabs on the pieces of wood glued together that can be cut off later.

One other thing that will help all of the parts go together better is to cut the top and bottom pieces of the barrel and the top of the ping pong ball reservoir to the exact same width on a table saw with a fence.

The stock, back grip and front grip pieces of wood are cut out and attached as shown in the pictures. I then used a spindle sander and a hand held microplane to shape the pieces to my liking.

Make the Handles

The size of the handles on the gun were determined using other toy guns that my kids already had. Using these for an example I checked these against the gun body that I currently had. I made them a little alarger so the gun would look a little oversized - almost comical.

I glued together pieces of baltic birch plywood to make a block of wood for each handle. Then I shaped them mostly with a spindle sander.

As a rule of thumb while you are shaping the handles you should check the shape often. It's much easier to take more wood off the handle than putting it back on or trying to adjust the rest of the handle to make up for taking too much off somewhere else.

Cut Out the Triggers

I designed the triggers based on the cad model for the ping pong ball guns. They are cut out of 1/4-inch thick polycarbonate material. First I used spray adhesive to attache the pattern to the side of the material. Then I rough cut the shapes with a band saw. Next I used a spindle sander to sand the pieces down to the proper size.

I used a small aluminum spacer in the pivot hole of the triggers to keep the machine screw from cutting into the polycarbonate. I thought this give them a longer life. I found the aluminum spacers at Home Depot.

Add the Laser Attachment

I was going to make a connection for the front of the gun under the barrel that would be able to accept different attachments. I designed a tounge and groove system with a couple screws making contact with a couple brass strips that would be able to transfer power. After working on a few of the parts I decided it would be better, and a lot faster, to just go ahead and permanently mount the laser to the front of the gun. I added more informatio about this potential front rail system in the following step in case someone wnts to attempt to build something similar.

This configuration is probably a little larger than needed, but I also needed to create a chase for the wires to get from the laser to the battery holder. I also needed to have space for the laser on/off switch.

It's probably easier to follow along in the pictures below than to explain it in a text description. As you look through the pictures you should consider that I tried to build this whole ping pong gun in a way that it could be taken apart and fixed or parts could be replaced. I think that turns into a situation where I might over-complicate things.

The laser I used was a 3.2 volt laser, but seemed to operate fine on 3 volts from the battery pack.

Potential Front Rail Attachments

I was originally going to create a rail type of system for the front of the gun under the barrel where the laser is mounted. I had planned on this being a tongue and groove type of system where you could change out the attachment on the front of the gun in a fast manner.

The BIG question I had to ask myself was "would it be worth all the extra time and potentially not finishing the gun for Christmas in order to add this feature to the gun." My answer was no, so I decided just to mount the laser to the gun permanently. I am including the information as food for though for anyone who attempts to build something like this.

The attachments would be located in the same location as the laser housing on the gun and the intent was to have several attachments that could be used based on what my son wanted to do at the time.

Laser Attachment : This one would use the same 5mW laser that is permanently mounted on the gun.

Additional Flashlight Attachment : This would be an additional flashlight attachment for the gun that would shine lights downward from the gun and would light the area in front of the person holding the gun as they are walking forward with the gun in the ready to fire mode. I was thinking red and white LEDs could be alternately turned on.

If you can think of some other attachments that would be useful then please post them in the comments section. I would like to find out what other people dream up.

Motors Assemblies

See the information in the MATERIALS section for where I found similar motor assemblies.

Using the 3D model I located the opening on one side of the gun barrel and then cut the opening out of both sides of the gun barrel at the same time. That way I knew the openings would match each other and be symmetrical.

I held the motor assemblies up to the sides of the barrels and marked the screw locations. Then I drilled the holes and attached the motors using machine screws. Once both motors were attached I checked the separation between the two rollers to make sure they were the correct spacing. If you need to space the motors out more you can add washers to the machine screws between the motor assemblies and the side of the gun barrel. While I didn't need to do this I did consider using some rubber washers or small wire grommets so there would be some compression in the material available.

The motor assemblies have exposed wiring and some capacitors so I decided to enclose this wiring using hot glue or a bondo type of material. I thought bondo might allow for some custom shaping of the assemblies and also helped to protect the wiring. I ended up going with the hot glue so I could more easily cover the wires and also be able o get t them a little easier if I needed to.

Finish the Trigger Mechanism

The trigger mechnanism was one of the most challenging parts about building this shooter. There is a lot going on in the area of the trigger and a lot of wires that supply power to the motors, LEDs, and flashlight. One other thing to consider is that there isn't a lot of room between the side of the gun and the ping pong ball. This means all of the wireds need to be installed as close to the corner of the barrel as possible to avoid interfering with the ping pong balls. I used a lot of hot glue to hold the wires in place.

I had to modify the original trigger mechanism slightly in order to get the roller switches to work properly with the tension of the spring that pulls the top of the trigger back. It was a balance between too much tension and not enough.

A #8 machine screw holds the trigger in place.

Check Your Clearances Inside the Gun

With the motor assemblies being attached to the gun it is time to check the clearances between the flywheels for the spacing of the ping pong ball. It is also a good time to test fire the gun. You want to make sure no other adjustments are needed before completing the rest of the work on the gun. A little time here can save a lot of time later.

This was really the moment of truth for me to find out if all of the measurements were correct. Everything worked out as expected for the separation between the rollers. The test firing of the gun also allowed me to test the trigger mechanism and plan for the routing of the wires and the switches that control the motors and the lighting.

One other thing this let me do was chase a few ping pong balls through my garage. Of course there was one that will never be found. I have no idea where it ended up after bouncing off 10 different things.

Add the Battery Holders

I added the battery holders as shown in the pictures. Each battery holder holds four "AA" batteries in order to get the voltage up to the 6 volts dc power to the motor assemblies. The battery holders I used were from radio shack. They do have their own on/off switches, but I didn't need the switching capabilities. I used a dremel tool to remove the part of the switch that sticks above the casing since it interfered with how I wanted to attached the cases to the ping pong gun.

I used some small wood screws to attach the battery box to the bottom of the gun. I drilled some holes through the battery holder in between the battery positions so the screw heads did not interfere with the batteries or the contacts. I used two #4 screws 3/8 inches long. These were just short enough that the screws did not protrude through the bottom of the gun into the barrel section where the ping pong balls come out.

Attach the Reloading Door

The reloading door on the back of the gun is opened to add more ping pong balls. It is held shut by two 1/4 inch diameter rare earth magnets that are aligned with two #4 wood screws. The holes for these wood screws are countersunk with a 1/4 inch drill bit so the screw heads can be adjusted up and down. This lets you adjust the screws so the magnets hit them at the right height for maximum holding power.

The door is attached to a hinge that is attached to the top of the gun. This is attached with #8 machine screws and nyloc locking nuts. I did cut the machine screws down so they wouldn't protrude from the bottom of the locking nuts. They would have interfered with each other if I would have left them their original length.

I added one machine screw sticking out of the door so that it can be opened. I worked on several options here, but this it what I came up with. A 3/4" wide fender washer makes it easier to grab and open for smaller fingers.

Add the Switches to the Back Cover

The motor assembly came with a three position slider switch. Positions are off, on at half power and on at full power. I decided to add this switch to the back cover of the gun. I marked the position where the switch was to come through the plate. Then I drilled a couple holes in the marked slot and cut out the rest of the waste material with a benchtop scroll saw.

I also added a pushbutton switch to turn the UV LED's on. I located the switch on the left side of the back cover a little above the slider switch. Placing it off to the side allowed everything to fit inside the gun body without hitting the trigger mechanism or trigger switches. This switch is the same as the switch on the front of the gun that turns the laser on and off.

Add the Trigger and Motor Switches

The trigger assembly does multiple things for the gun. It turns on the motors to the drive wheels, it pushes a ping pong ball into the rollers, and it holds the next ping pong ball to be fired out of the way until the current ball has been fired and the trigger returns back to the ready position. The trigger also releases a switch that turns on the UV LEDs so the glow in the dark ping pong balls can be charged up.

Both of these switches are the same type of lever switches with small rollers on the ends of the levers. These switches are great for this application as they don't take a lot of force to close the contacts. Also, they can be set up as NORMALLY OPEN or NORMALLY CLOSED.

I had to add a small piece of wood behind the switches for something to attach them to. I used a #4 machine screw through the holes on the lever switches into the backer piece of wood.

Add the Flashlight

I founds some great flashlights at Home Depot that had white, green, and red LEDs. The button cycles the flashlight through white, red, green, and flashing red modes. I cut the flashlight body down so I could mount it on the front of the gun. I used a hacksaw to cut through the aluminum casing. It was fairly easy. After cutting I used my belt sander to smooth out the cut edge and get rid of the aluminum burs.

I soldered wires to the contacts of the flashlight so it could run off the AA battery pack that runs the motors. The flashlight was designed for 4.5 volts dc so I ran separate wires tapped into 3 batteries in one of the battery packs to the flashlight head. This allows the flashlight to be run separately from the other items feeding off the same battery pack.

I made a mounting cradle for the flashlight case by cutting a circle the same diameter as that of the flashlight casing. Then I cut it down to the size I wanted and mounted it to the top of the front of the gun. See the pictures for mounting details. The Mounting cradle had to be sized to the section of the handle with a constant diameter. There were some small ridges on the body of the flashlight that were slightly larger in diameter.

I added an 1/8 inch thick disc of wood to the front of the gun body where the flashlight attaches. The disc is just slightly smaller than the inside diameter of the flashlight body. This holds the end of the flashlight securely in place once it is attached to the cradle with hot glue.

The cradle holder for the flashlight is attached to the top of the barrel with a couple #4 wood screws that are countersunk into the top of the barrel to keep the screw heads out of the way of the ping pong balls being fired. I drilled a small hold through the wood disc in which to feed the two wires for power. These wired had to be routed to the back of the gun and then to the front battery pack.

Add LED Lights to the Gun

I added 5mm ultraviolet LED lights to the inside of the gun to charge glow in the ping pong balls. The glowing balls flying across a dark room are really cool looking. An added effect is the ultraviolet glow coming out of the barrel of the gun.

I just attached the UV LEDs with hot glue to keep things simple and help protect them. As you can see in the pictures, the inside back corners of the gun barrel make a great place for the LEDs. The UV LEDS are in all four corners behind the ping pong balls and charge up right before they are fired. It only takes a second to charge up the glow in the dark balls.

The ultraviolet LED lights turn on automatically when the trigger is pulled slightly. You could add a switch to turn these light off if you want or don't even install them if you want to save a little time and money on the build.

I was going to add some 3mm red and green LEDs to the top of the gun as an aiming device. The plan was to put two red LEDs at the tail end of the top of the gun and one green LED at the front of the top of the gun. When the green LED is sitting between the two LEDs then you know you are on target. I decided not to add these since I was already adding the laser targeting system. I thought this might be something that could be added later if I wanted.

Make Your Own Glow-In-The-Dark Ping Pong Balls

I only had a dozen of the cheap glow in the dark ping pong balls. I decided I had better get more since there wouldn't be enough to fill both of the guns if I ended up making one for my other son. Besides, it seemed like it would be better to have too many of these than not enough.

I searched for more of these online and also at a couple local sporting good stores and couldn't find any that were reasonably priced or had good reviews. Some of the reviews said they didn't glow very well. I decided to get a bulk quantity of decent ping pong balls that I could cover with glow in the dark paint and any remaining ones could be used for actually playing ping pong.

I ended up ordering a pack of 144 GOGO 3 Star 40mm Blank White Ping Pong Balls from Amazon. They had a good rating and the white color would make for a good background for glow in the dark paint.

I searched for glow in the dark paint and found a couple sources. The one I used was Glo Nation.
http://glonation.com/unpigmented-glow-paint.php

Their prices were much better than some of the others and that allowed me to get a couple different colors of glow in the dark paint. I got a half ounce of green and orange. I thought it would be fun for my kids to paint the balls different colors and maybe give some of them stripes.

I painted the first set of balls with two coats of paint and was not happy with the results. The paint is thick and does add some thickness to the ping pong balls and I didn't want to have ping pong balls of different thicknesses. The paint also created a rough surface on the balls. I think this might slowly damage the surface of the cushioned wheels. Lastly, the glow effect of the balls was not very uniform.

My advice is to just buy pre-made glow in the dark ping pond balls. You will save a huge amount of time and probably be money ahead. The ones I found at KMart work just fine and are a regulation size of 40mm. I found several packs at my local store, but call ahead as not all stores carry them or they may be out of stock.

Add Ping Pong Ball Stops

With adding some type of "Stop" to the gun in front of the wheel assemblies, the ping pong balls would roll forward and shoot out of the gun without having to pull the trigger. My fix for this was just to take a small section of 3/8 inch diameter backer road, cut it in half lengthwise, and hot glue a piece on each side of the barrel just before the rollers. The backer rod I used is a closed cell foam. It is firm, but compresses as the trigger pushed the ping pong balls in between the two pieces. Once the balls get past the foam they make contact with the wheels and shoot out of the gun.

Paint

This ping pong gun hasn't been painted or finished with anything. Currently it is just bare wood. I think it is fine for the type of toy that it is and also help it no being mistaken for a real gun. I don't think that would happen anyway.

I would like to get some suggestions from the knowledge base here as to what painting or finishing options other people would go with. I am leaning towards some type of metallic finish paint. Please throw ideas at me.

Have Fun!

Now it's time to have some target shooting fun. Since these do have lasers on them, even though they are very low power, you should not point them at anyone else. That is the main reason I put the ON/OFF switch on the laser sight.

Options for the future:

If you have any suggestions for the next one I am going to finish for my younger son then please post a comment. I would love some feedback and any ideas you may have.

I would love to be able to make parts for the next one using a 3D printer or cut some parts out with a laser cutter. I think some 3D printed parts could add some great detail, cut down on some of the bulk and weight of the wood, and maybe help create a design that other makers could print on their own 3D printers.

Have fun!