DIY Dog Pull Cart Made Out of a Folding Bicycle Trailer.

This is the trailer cart I made for my dog Thunder.
It's a folding bike trailer, I made a harness and rigging for him to pull it places.

Aside from the trailer and green dog harness, which I already had, I spent $18 total to make this rig. 

A lot of engineering went into this project. If loaded correctly this produces as little as 1kg of downward force on my dog. The poles are only for weight and steering. The upper leads pull the cart slightly forward and move the centre of gravity for propulsion. My dog also has breaks connecting underneath his body which allow him to stop the cart. Finally thanks to Archimedes; Even a completely unbalanced load of 10 pounds will only exert 4 pounds of force spread over a harness with over 3 ft square relative weight distribution contact in the rigging.

Step 1: The Supplies

You'll Need:

- Folding Bike Trailer. I originally purchased mine for groceries and laundry.

- Dog Harness. Originally purchased to roller blade together. Most any decent harness will do. On mine, I added a metal loop to the bottom (for brake lines), and a pad to the top, and that's it.

- 2 poles. These serve two purposes; 1) They transfer weight to the animal, 2) They help the dog steer the cart and provide a "zone". The poles must be strong enough to transfer the weight, but light enough to not affect total mass. I chose 2" bamboo stalks.

- 8 leashes thick enough to be useful.

- 6 collars of the same size as leashes, to be used for their adjusting hardware.

- 2 eye screws, I chose PVC coated for comfort. The key to these is not just the size, they need a flange at the base of the hook

- Electrical / PVC tape

- matching yarn, Acrylic is best.

- liquid fabric glue

- Cheeky Licence Vanity Plate

- Finally, a happy dog.

Step 2: The Extender Poles

This area took the longest to figure out.

I needed something entirely removable and yet strong enough to do the task. First I tried broom sticks and bungee cords, just to see if my dog would take to it at all. Turns out, he loved it a lot. I tightened everything up and secured the broomsticks with electrical tape so I could sort out the harness. If you choose broomsticks, I reccomend plastic ones, the metal ones seem to kink easily and become useless. Plastic will just bend. Plus most broomsticks today come with swiveling holes in the handles, making things easier to dream and hook up. 

They just look like broomsticks. Remember the more professional you make your rig look, the less likely you'll be interpreted as being cruel.

Tape a grip pattern into the base of the poles, this will help secure them with a lashing later.

Step 3: The Trailer Brake

You'll need a secure mounting point for the eye screws so once stopped, the trailer won't roll into the dog. It will be stopped by the Brake Straps.

This method I thought of while thinking about wicker furniture. It's like a fiberglass binding
I pre-drilled and sunk the screws into the bamboo about 4" from the top of the pole. I then applied glue liberally to the last few threads and finally again all over the base flange of the screw and tighten flush. Now wrap the flange to the bamboo with the matching yarn. Wrap liberally and sink into the glue pool. Once a nice wet mound of thread binds the eye screw, wrap the bamboo evenly for aesthetic and tie off the end. Cap each side of the wrap in a neat layer of PVC tape for finish and security.

At this time wrap the end nob of the bamboo in PVC tape to prevent scraping and increase comfort levels.

Step 4: Mounting the Extender Poles

- Slide the poles through the frame and into the basket weave of straps holding the shell and seat to the frame.
        **- Make sure to use the frame for the shell to create tension.

- Loop a strap around the grip you made before reinserting it.

- Once the poles are even, tighten the seat straps, and your poles are securely mounted.

Step 5: Making the Hardware.

Take out those leashes and collars you picked out earlier.

Take a pair of sisoros and cut the adjusting hardware off the collars.

Then remove the hand loop from two leashes. Connect them to the shell frame with a set of hardware. These become the Pulling Leads.

Cut 2 different hand loops off at about 2 ft. Then cut the clips at the ends of scrap off. Use sets of collar hardware and clips to make your adjustable Load Straps with clip ends Make 2 loops out of scrap just big enough to fit over the end. These help lock onto the bar by sliding up and down.

Cut 2 leashes at about 1ft, then cut off the clips from the remaining 2 leashes. Use collar hardware to make double ended straps for the Brake Straps.


REFERENCE: In hanging picture: Hanging L-R: Load Strap, Brake Strap, Pull Strap, Pull Strap, Brake Strap, Load Strap.

Step 6: Hook Up Your Pup.

First hook up the load loops on the side to the top harness ring. Then the Pull Straps to the top ring.

Finally connect the Brake straps to the lower harness ring and the other end to the pole mounting point.
    - Use care here. Adjust your straps so that the harware doesn't hit your dog's legs every step, but short enough to pull to a brake.

Step 7: Make a Final Statement

Pick something funny for the back of your cart. A joke, or a play on words really keeps people thinking about you positively.

Congratulations, Now you have a professional looking trailer for your doggie, and still have a usable bike trailer as well.

Keep loads light and spirits high. Remember there's a thin line between well trained and abused animals.




Keep checking in for updates, modifications and the big ALL SEASONS CONVERSION.

Step 8: MODIFICATIONS & UPDATES

Truth be told, this design won't be considered final until next summer (2012). Some will be mods because of dog growth, Some will be for practicality and general improvements. The biggest mod upcoming will be the ALL SEASONS CONVERSION.

Updates & Mods in Planning:

- Upgraded Weight Belt (and raincoat from scraps)
- Frame Mod - Center Wheels
- Bigger Wheels, same hubs
- 4 SEASON CONVERSION

Step 9: Optional Frame Mod - Metalwork Skills Required

I did this step while still in the design phase. I don't have many pictures of it, but I'll do my best to show you what I did.
Basically take the hanging axle bracket and raise the axles to go through the frame.

PROS: Lower center of gravity. Easier load distribution, Better overall handling.

CONS: Frame is lower to the ground making obstructions and grass harder to traverse. Requires future body painting.
                  (can all be solved by installation of a bigger wheel, future MOD)

First
- Strip your trailer down to it's basic frame. (remember where everything goes, take pictures if unsure)
- Remove wheels.
- cut the 4 welds securing the bracket in place.
- Measure and mark the centre of the frame.
- Temporarily mount the bracket and mark out the new axle holes.
- Remove bracket and drill 5/16 hole for axles.
- Pre-drill and rivet in place. I used 16 rivets per bracket. It should be stronger than before.
- Replace wheels. grinding holes for fit and finish.
- Reassemble the trailer, You're Done.