Dogzooka Robot Dog Ball Launcher

"Pixel", my faithful pet Schnoodle (Schnauzer/Poodle mix) is a bundle of energy. She LOVES to play fetch and will faithfully execute her retrieval duties indefinitely - if you're willing to indulge her. She wears me out!

I designed and built a device that would allow me to play fetch with Pixel for extended periods without throwing my arm out of joint. You can purchase dog ball throwing devices, but they're expensive and made of plastic, and they lack the “wow” factor of the Dogzooka. They also keep you tethered to a wall outlet if you want extended play - something I wanted to avoid.

My version was inspired by the common Potato Gun. If you're not familiar with these shade-tree WMD's, then Google it! Your mother/wife/partner will thank me for opening your eyes to new and interesting ways to hurl tubers at high velocity.

The Dogzooka is based on a "coaxial piston". Besides being surprisingly simple, it is both elegant and compact. Launch the following Shockwave demo and you can step through all the phases of operation of a Coaxial Barrel. You may have to install the Shockwave Flash plugin. Coaxial Piston step by step demo

Although I cannot take credit for the coaxial design, my implementation has been automated using electronic circuits, relays, and electric solenoid valves. I've also implemented a breech-loading design (most potato guns are muzzle-loaded, which wouldn't lend itself to this application).

The Dogzooka is powered by a standard 20 oz. Paintball CO2 canister and one fill ($3 at Dick's Sporting Goods) yields about 100 shots. At 20psi, the ball travels about 50 yards - much further than I could throw it. I did crank it up to 60PSI once (see slow motion video above). It sent the ball soaring into the next county.

I scavenged most of the raw materials on the cheap from a nearby metal recycling yard. I was able to use all stainless steel components and only spent $18 (charged by the pound). NOTE: this design could be duplicated in PVC, although you'll have to improvise on some of the components. Warning: over-pressurizing a PVC cannon can be dangerous!

Originally, I set up the device to automatically detect the ball in the chamber which would allow the cannon to operate in "unattended" mode like the commercially available models. In this mode the dog (or cat, or opossum, etc.) drops the ball into the chamber and it immediately launches the ball. It would be fun to watch your dog play unattended, but a cursory look at customer feedback on the retail units revealed that almost all reported that their dogs were startled when the ball was immediately launched; consequently, it was very difficult to train them to get close enough to drop the ball in the hopper. I found this to be true with my dog - so I opted for a remote control option so I could control when the device launches.

To reduce the "Swooooosh" from the high-pressure air escaping, I added a lawnmower muffler to the dump valve and a perforated muzzle on the business-end. To be honest, I'm not sure it helped, but it gives it an aggressive "military" motif.

This Instructable can be cobbled together by anyone with a modest amount of mechanical savvy. No knowledge of electrical circuits is required. My MIG welding skills are very basic. You can always smooth/grind down your amateurish looking welds and they'll look as if a seasoned pro did them. I finished the project with an automotive wrinkle paint that is very forgiving when it comes to hiding blemishes.

Thanks for reading my Instructable!

Here's the component inventory:

Raw materials from Metal supplier (scrap recycling facility suggested)

• 20" length of 4" ID Metal Pipe (for exterior pressure tank)
• 20" length of 1 3/4" ID Metal Pipe (for barrel)
• 4" length of 3.5" OD Metal Pipe (for CO2 bottle holder)
• 2" length of 2.5" OD Metal Pipe (for downpipe from hopper)
• 4" Diameter disc with 1 3/4" center hole made from 1/16" flat sheet metal (for front pressure tank cap)
• 2.5" OD Metal Pipe "Tee" (for breech chamber. Downpipe and barrel attaches to this)
• 2" X 2" flat 1/16" sheet metal (for breech chamber cover)
• 4" X 4" flat 1/16" sheet metal (for breech chamber cover guide plates)
• Misc. parts to construct suitable stand (e.g. metal skids, legs, etc)

Items from Home Improvement store:

• 4" Pipe Plug X 2 (for Piston) Link to item
• 2 5/8" Rubber washer (for seal between tank and barrel Link to item
• Silicone Glue (to glue gasket to piston)
• Offset Plastic Funnel (for hopper) Link to item
• 3/4" Brass Tee (for splitting off fill and dump solenoids)
• 2 Part epoxy (to help seal pressure tank on the inside around the breech chamber)

Items available via internet:

• Bulk pack of 12 Tuff balls Link to item
• 4" Sanitary Pipe Tri-clamp with ferrule (for rear access hatch)
• 3/4" 12V Solenoid Valve (for Dump Valve) - Ebay
• 1/2" 12V Solenoid Valve (for pressure fill valve) - Ebay
• CO2 Regulator (to meter the tank pressure) - Ebay
• 20 oz Paintball canister (to pressurize tank)
• Paintball remote mounting kit - includes braided line and high pressure female fitting Link to item
• 12V Timer circuit with relay (to time the fill and dump sequence) - Ebay
• 12V Remote control relay transmitter and receiver (to activate timer circuit) - Ebay
• Mini Pneumatic ram (to close the breech chamber when pressurizing tank) - Ebay
• 5/16" brass fittings and nylon tubing (to connect pressure tank to pneumatic ram)
• Lawn Mower Muffler (to reduce dump valve noise) - Ebay
• Small plastic box (to contain/protect electronics)
• Battery pack for 8 AA Batteries (to power the electronics and solenoid valves) - Ebay

Tools required (for Steel construction)

• Drill motor
• Handheld Cutoff wheel (electric or pneumatic)
• Metal Cutoff saw (can substitute hacksaw or cutoff wheel)
• 4" Hole Saw (can substitute cutoff wheel) (to cut the OD of the end plug)
• 2 1/2"" Hole Saw (can substitute cutoff wheel) (to cut the hole in the pressure tank for the chamber "UP" pipe)
• 1 3/4" Hole Saw (to cut the barrel hole in the end plug)
• MIG Welder
• Hand tools - (e.g. wrenches to tighten fittings, etc.)

• Fig. 1 - Cut the top of the TEE so the length of the "up" pipe is 3/4". Cut the front extensions to 2" and the rear extension to 1". The "up" pipe needs to be short enough so the entire TEE can slide into the rear of the 4" tank yet be tall enough to protrude through the hole in the top of the pressure tank when you center the barrel. See figure 4.

• Fig 2 - The Breech chamber diameter (2.5") is larger than the barrel (1 3/4" ID) to allow the small dog balls to easily drop down from the hopper and enter the breech chamber. The barrel diameter of 1 3/4" is slightly smaller than the small Tuff Balls, which maintains the tight seal in the barrel during firing. The barrel where it mates to the breech chamber needs to be expanded to mate with the ID of the breech chamber. It needs to be a snug fit. I took the barrel pipe and the TEE connector to my local muffler shop and they expanded it for free. Weld the seam at the end of the chamber to join the two pieces.

• Fig 3 - Using a hole saw, cut a 2.5" diameter hole in the pressure tank pipe. Drill a 1/4" center pilot hole 4" from the end of the pressure tank.

• Insert the breech chamber/barrel assembly into the pressure tank and lift the assembly inside the tank so that the "UP" pipe protrudes through the hole cut in Fig 3.

• Center the barrel in the pressure tank and tack weld the "UP" pipe to the pressure tank.

• Construct the pressure tank end-cap by cutting a 4" disc with a 1/3/4" hole in the center. Slide this "donut" cap over the barrel and tack weld to front of pressure tank. Note: on the bazooka I built, I used a reducing cone instead of a donut for a more appealing aesthetic.

• Fig 4 and 5 - Finish welding around the "UP" pipe and front pressure tank cap donut. These welds must be air-tight. Once the entire assembly is complete, you can pressure test the tank using soapy water to detect leaks. Note: photo is from prototype cannon - not the final design.

• Using the two 4" End Cap plugs, assemble the piston valve. You will use one of the end caps and the rubber ring from each "kit" to make the piston. Using silicone glue, attach the rubber gasket to the piston.
• The piston fits into the rear of the Dogzooka and travels about 1/2" forward and backward. During the pressure fill stage, the piston is forced against the back-side of the breech chamber, sealing off the chamber. Enough air passes around the piston rings to pressurize the tank once the breech is sealed off.

• Fig 1 & 2 - Butt weld the short flange (aka the "ferrule") from the tri-clamp set to the back of the pressure tank. Grind any slag or debris that may be present inside the pressure tank around the perimeter of the weld. This is where the piston slides, and you want this area to be smooth. You can use motor oil to lubricate rear chamber so the piston moves freely.

• Fig 3 - Drill a 3/4" hole in the middle of the tri-clamp cap and install the brass Tee with the male nipple going through the hole. Install a shallow nut on the inside of the cap to secure the brass TEE.

• Screw the smaller 1/2" electric solenoid into the female end of the brass TEE that is facing towards the rear of the assembly. You can use 90 degree elbows to position the solenoids so they are tucked neatly behind the tank. Use Teflon tape to seal the threads.

• Screw the larger 3/4" electric solenoid into the female end of the brass TEE that is facing 90 degrees upwards. Install the muffler to the female threaded opening of the solenoid. I drilled larger holes in the muffler when I discovered that the smaller holes restricted the air from exiting quick enough to move the piston valve. You may have similar results.

• Wire the Remote control relay by following the Fig 1 illustration. What we are accomplishing here is a 12V positive signal to the timer relay when the remote control button is pushed.

• Wire the Timer relay circuit by following the Fig 2 illustration. The timer relay activates when it receives 12V from the remote control relay. It then energizes the output wire to the pressure fill solenoid for XX seconds. The pressure fill time is adjustable using the pot on the circuit board. I found that about 5 seconds was ideal. After the timer interval is reached, the 12V output going to the dump solenoid is energized and the tank fill 12V output is turned off - triggering the firing of the Dogzooka.

• Package the two circuit boards into a black box for protection and attach to the rear assembly via tie wraps. Make sure the antennae is routed to the outside.

• Attach the CO2 Regulator low-pressure output to the input of the 1/2" solenoid.

• Attach the tank adapter end of the remote adapter to the high pressure input of the regulator.

• Screw the Paintball canister into the tank fitting of the remote adapter.

• Fig 1 - Construct a chamber door using 1/16" sheet metal that is 2 1/2" wide - enough to cover the chamber "UP" pipe.
• Fig 2 - Fabricate the chamber door "rails" to guide the door into the correct position on top of the "UP" pipe. I used some sheet metal angle I found at the scrap yard. Weld the rails to the tank.
• Fig 3 - Weld a mounting tab to the top of the tank for the pneumatic ram.
• Feed the ram through the mounting tab and secure with set screw.
• Mount the end of the ram arm to the chamber door.
• Using a short piece of 2 1/2" pipe, tack weld it to the top of the chamber door rails. This is the "feed" pipe to the chamber.
• IMPORTANT - Alignment is critical - ensure that the ram and chamber door moves freely forwards and backwards on the rails. Watch the video in this step and notice how the chamber door slides back and forth.
• Fig 4 - Weld a bung on the side of the pressure tank to provide a place to connect the air line to the ram.
• Run 1/8" pressure line from the bung to the end of the ram.

• Construct an adjustable stand for your Dogzooka. The stand should allow the angle of the device to be adjusted.up/down to control the arc and distance of the ball launch. I welded 3/8" bolts to each side of the pressure tank and used nylon lock nuts to snug the legs enough to allow for adjustment.

• Attach the battery pack to one of the legs or to the underside of the pressure tank. I used a hot glue gun.

• Nuff said!