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a mobility scooter with a dog trailer attached.

Attaching a Dog Trailer to a Mobility Scooter

The client wrote, “I have dystrophic epidermolysis bullosa recessive (EB). It means my skin shears off or blisters at the slightest touch. I can’t manage fiddly things like catches etc. I was diagnosed at birth. Any damage to my skin risks incurable skin cancer.”

The client has a new mobility scooter, and new to her, trailer for her Canine Partner assistance dog, but with no immediate means of connecting the trailer to the scooter.

As the client has limited use of her hands, any solution needs to address her limited dexterity and the fragility of her skin.

The Challenge

The author considered, after reading the Case Sheet and before making his first site visit, making a lightweight, 3D-printed ball hitch for the trailer, and started to model some ideas in SolidWorks. However, after visiting the client and seeing the scooter (a Kymco Maxer), trailer (a Papilioshop Argo), and available parts, he revised his plans.

The trailer is designed to be towed behind a pushbike and has a fixture that is designed to mount to the rear wheel axle.Trailer manufactures image, the trailer attached to a bike.

The trailer is supplied with a Clevis-type pin with a very strong captive spring clip which the author found difficult and, at times, painful to use. It was obvious that the pin as wholly unsuitable for the client. The author sourced two alternatives to the supplied pin, a Clevis pin with a captive clip, but of a different design, a design that permitted the addition of a 3D printed tap that would reduce the point load for the client, and a ball locking pin. The ball locking pin being modified by the addition of a 3D printed button, bonded to the plunger, to reduce the point load.

The trailer is supplied with a small simplex dog clip which is used to secure the trailer safety lanyard. Again, the author considered this as an unviable option for the client and procured three potential options.

The solution

The “bumper” tubes on the back of the scooter permitted, with the use of bespoke Additive Manufactured (AM) parts, a non-invasive solution to mounting the standard trailer hook*, an M12 fixing passing between the two bumper tubes.

*Translation from the description on the Italian manufacturer’s website. Other retailers describe the part as a “trailer hitch”

Measurments and Printing

Measurement of the bumper was achieved using a digital calliper and clinometer app on the author’s phone, the lower tube not being directly under the upper tube.

The author designed the mount for the trailer hook as one part, cutting it in two as the last design feature. The model exported as an STL file as a single part. The part was imported into Chitubox slicing software to produce the print file.  Given the potential issues with print shrinkage, the author printed a test piece that he could offer up to the scooter bumper to ensure that the finished part would fit the bumper.

After confirming the fit of the part the author printed the parts (11 hours and 41 minutes) in Chitu Systems Conjure Rigid resin, the author has found this resin to be an excellent, non-brittle, product with very low shrinkage, however, it is very slow to print.

Assembly

To facilitate assembly to the scooter, after post-processing of the printed parts a repair washer was bonded to the front-facing part, and the hook/hitch to the rear-facing part with Araldite 2014-2 two-part epoxy. The ball locking pin button being bonded at the same time.

CAD section image of the button.The locking pin button was designed with a soft transition fit to the ball locking pin button, a cavity to accept adhesive and a vent hole to permit the excess adhesive to be purged from the joint. To ensure the bottom profile of the AM button was correct the author used a 3D scanner to enable him to measure the radius of the concave depression in the top of the ball locking pin head.

The standard trailer lanyard proved to be too short so the author extended it with a short length of paracord, with heat-shrink-sleeving shrunk over the knot.

The author did not have tools with him to enable him to remove the standard dog clip from the trailer lanyard, the alternative to the clip being a lightweight Carabiner.

Trailer attached to the scooter, with the extended lanyard also attached.

 

The benefit

The client is now able to attach the dog trailer to her mobility scooter with relative ease, permitting her to take her dog to the nearby beach without the need to use a car and independently – without help from her husband.

She says: “I’m thrilled with what Martin has done. The new connector is absolutely amazing. It keeps us safe in the trailer as well.

Thank you once again for helping me maintain my independence.”

 

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