Important Note: This cart must be customized to fit each specific dog. The files I provided are more of a guide to help you build a custom cart for your pup. If you are unable to design your own cart you can submit a request at Bubbles2Legs. I will design and also print a custom cart for your pup in need 100% free of charge.
On a Sunday morning last summer I awoke to an unfamiliar little squeak. Half awake I look over and notice a new little new born puppy on my wife's head. We grab tiny bubbles and her mother then place them in the whelping box completely missing the fact that Bubbles was very special. It wasn't until the next puppy was born that we noticed Bubbles legs or the lack of. At first we were unsure what to do but a quick internet search calmed our nerves. After a few months had past and a many failed attempts at building a wheelchair more conventional ways we purchased our very first 3D printer. Many many more failed attempts later I have came up with a design that is perfect for my Bubbles. It is light weight and stable without placing to much weight on her extra long dachshund back. She gets around in her cart better than any other small dog I have seen missing there front legs. Up and down hills and running threw thick grass taller than her nothing slows her down. Following our success with Bubbles and learning just how many dogs are out there in need of cart. My wife and I want to share what we have learned in hope that a dog wont be throw to the curb due to this simple disability.
In this instructable I'll show the measurements required to design the cart along with the basic assembly of the cart and how to fit it to the dog. Plus some bonus videos of it in action. If your pup is about the size of Bubbles it should be a simple print and play. If not I can be contacted at Bubbles the two legged wiener dog to help design a custom cart for your pup and even print it if you do not have the resources.
Step 1: Getting the Measurements - Chest
Getting accerate measurements is a very important step as proper fit is key to a comfy and safe dog. If you our designing the cart yourself with the dog then it's easy to just take the measuments but if you're take them to send to someone else it's best to use pictures so the designer can get a feel for the dog.
First measuments that are needed is of the cercumferance of the chest and the length of the rib cage. With those the basic shape of the main frame can be made. Then a third measurment of the width between the nubs on the chest.
Step 2: Getting the Measurements - Chest Cont.
Then a third measurement of the width between the nubs on the chest. This shows how big the cutouts need to be to allow room for what nubs they do have. (Be careful to not get bitten as they may not be to happy about this whole process.
Step 3: Getting the Measurements - Height
For getting the height you want to hold the dog in a natural standing position. Be sure the legs and back a straight with the chest at a natural level. The proper height is extremely important for the designing of the fork for stability and comfort. Adjusting the height of the fork and the angle that it mounts to the frame can completely change how it works for the dog. Dog seem to be tipping forward? Well check the height and maybe make it a little taller. Or angle the forks more forward. The opposite goes if it seems like to much weight is being placed on the dogs back.
Step 4: Parts
I Have included the STL as well as the source files from Solidworks. The fork and shim are very easy to customize using solidworks editing some of the early sketches. The frame on the other hand is a whole different story. It has evolved many times and the sketches are a mess.
Frame x 1
Fork x 1
Fork shim x 1
Fork Nut Plate x 1
Stop x 2
Rim x 2
The main printed parts are the frame, fork and the rims. The other printed items aren't completely necessary but help in adjusting and using the cart. They are the strap loop and spacer.
Non Printed Items:
M5 nut x 2
M5 locking nut x 2
Bearings size 5x14x5 x 4
M5 x 35 Pan head machine screw x 2
Flat Phillips Machine screws 1/4-20 x 1-1/2 x 2
hex Nut 1/4-20 x 2
1 inch nylon strap x enough to wrap around dog about 4 times
3mm thick craft foam sheet x 1
Double sided velcor x enough to wrap around dog about 2 times
sewing kit x 1
spray glue x 1 can
superglue x 1 bottle
Step 5: Making the Straps
Update: The way the straps are installed has change which makes building of the cart much simpler. Be sure to read notes on pictures.
The straps are made of 1 inch wide nylon strap I bought from Hobby Lobby. There are two main straps and each needs to be roughly 1.5 times the circumference of the chest. On one end a metal loop will either be sewn or glued on with super glue. Once that is done you will want to place the strap in the frame as shown and mark the edge of the frame on the strap. Now that you have that marked you need to measure the distance from the strap loop to the mark you made along the inside of the frame. With that measurement lay the strap out and add the difference from the total circumference and the distance along the inside of the frame starting at the mark you made on the strap. Fold the strap at the circumference mark. With the strap folded back onto itself cut the extra where it lines up with the mark from the edge of the frame. Now the metal loop will fit at about where the fold is and the other mark shows where the edge of the frame will be. Knowing that you can attach the velcro. Copy that strap tp make a second.
The optional third rear strap is very simple. It is made using double sided velcro and needs to go around the dog and overlap a few inches. Then just cut the width so it with fit in the two rear slots.
The third strap is not installed till later and a thumb tab can be printed out and sewn on for easier use.
Step 6: Adding the Chest Padding
I guess this part isn't completely necessary as you could just use a prosthetic sock but here in Texas its nice to be able to go without a sock.
First take the spray glue and coat the back of the foam sheet. while that drys I like to cover the straps out so they don't get any glue on them. Then carefully place the foam into the frame pressing it in and working from the middle out. You can then go around and trim the extra off. I like to leave about a 1/4 inch that I will pull around the edge and superglue. Let dry and trim flush with bottom. Doing that makes sure that any part the dog skin touches should be covered in foam.
Finally cut slits for the fork bolts and the rear strap. You can now install the rear strap as pictured. Just ensure that the soft side of the velcro is on the inside towards the dog.
I have also had luck with different kinds of fabric. Main thing is to use something that will conform to the frame.
Step 7: Assembling the Cart
Now you're almost to the fun part. All that you have left is to assemble your pups new cart.
The video covers most of the assembly besides the new shim design for the fork. Its a couple more small parts nut now the fork angle can easily be changed with just a simple shim.
1. First step is to install the 5mm bolt into the stop and then into the fork. Due to the tight space a stubby or 90 degree screw driver can be very helpful. As you thread the bolt through the fork you will want to install one plain nut on each bolt. Continue tightening the bolt down lining the teeth on the fork and stop up till secure insuring that the nut lines up into the cutout in the fork. The stop will need to be adjusted with the dog to insure it prevents the dog from tipping onto its face but still allowing movent.
2. Now its time for the wheels. Each wheel rolls on an identical inner and outer bearing. The easiest way to press the bearing into the wheel is to use a 5mm bolt and a couple over size washers to squeeze the bearings into the wheel. You will want the over size washers to make sure you are only putting pressure on the outer race of the bearing. With bearings installed its time to place the wheel onto the fork. Then place one locking nut on each bolt and tighten till it just makes contact with the rim. Now spin the wheels and watch how well they spin. If the seem to drag try loosening the nut just a little. If they spin free but the wheel has a lot of side to side wobble try tightening the nut. Continue adjusting till your wheel spins freely with little wobble.
3. Third and final step for assembling the cart is simple installing the fork onto the frame. On the frame you will see some holes. The number my very depending on the design of the cart. Pick two that are side by side place a large machine screw in each one from top to bottom. Now install pick a shim you would like to try out. ( angle of shim adjust angle of the fork) Install the shim over the bolts aligning with the holes. The fork is next insuring the stops are facing forward. Finally the nut plate and nuts. Tighten everything now ensure all the alignments pins line up.
Step 8: Installing the Pup and Adjusting
Placing the dog into the cart is pretty straight forward. Place there chest up against the front of the cart insuring there nubs and shoulders clear the cart. Then strap them in. The straps need to be secure but be very careful not to over tighten and injure the dog. If your cart has a third stap it is fastened loosely towards the hip to help support the cart and keep it level with the dog.
Now the moment of truth. The moment you have been waiting for since you fell in love with your little two legged companion. Its time to place them on the floor in there new cart.... and nine times out of ten they just look at you scared not having a clue what to do. But no worry with time, proper training and adjustments they will learn to use there cart. With them now in there cart take a good look at how the are standing. Make note of if there back is straight or if there front seems to be to high or low. If the cart is not sitting right it will really affect how fast they learn.
Examples of problems and how to correct them. The main issue is sagging or curling the back.
Sagging the back can be due to the wheels being angled forward to far, the forks being place to far forward on the cart, the cart need more support in the rear or simply the dog just has to get used to it. Fixes are to decrees the fork to a lower number (Less forward angle), more the forks to mounting holes further back, modification of the frame of the cart and practice with the pup helping them stay level.
Curling is the exact opposite of sagging. So to remedy you would increase fork number, move the forks to more forward mounting holes and again just work with your dog to try and get them used to it. One extra cause for curling I have seen is the forks being two short and the front of the dog being to low. Easy fix is to install a space between the fork and frame or replace the fork with a taller one.
Step 9: Carts in Action and Upcoming Updates
Here are some pictures and videos of some of the pup in my cart.
I'm always working to improve my carts. I work to make them easier for the dog and easier to produce while keeping the build cost a low as possible. One of my newest ideas I'm working with is making the frame extendable. This will make it possible to print carts for larger dogs on smaller printers as well as adding another way to adjust the cart for the dog.