Adaptive Bicycle for Indoor Cycling With Custom 3D Printed Pedal Assist

Our client is an active cyclist and former triathlon athlete who suffered a stroke and now has limited mobility on the right side of their body. To continue being active despite these limitations, they setup their bicycle as a stationary bike inside their house. But mounting the bike is challenging as is keeping their right foot on the pedal. This Instructables shows how we modified the stationary bike and mounting setup to fit their needs.

*Note that all designs used were made and sized specifically for our client. Additional sizing modifications may be needed to fit your specific circumstance.

Materials

• 1/2 4 ft. x 8 ft. Oriented Strand Board
• Non Slip Furniture Pads for Hardwood Floors, Cuttable Self Adhesive Silicone Anti Skid
• Rust-Oleum Stops Rust 12 oz. Flat White Clean Metal Primer Spray
• Pittsburgh Paints & Stains® Ultra Exterior Satin White Latex Paint & Primer - 1 qt.
• Wood Screw: #8 Size, 1 in Lg, 18-8 Stainless Steel, Flat, Phillips, ASME B18.6.1, Phillips, 100 PK
• Gorilla 8 oz. Wood Glue/Epoxy
• Super Glue 0.21 oz Plastic 2 Part Bonding All Plastic All Materials Clear Tubes (each)
• Any Type/Color PLA Filament
• Bike pedal toe cap similar to this one (our client already had a toe cap, so this was not something we had to purchase)

Tools

• 3D Modeling Software
• 3D Printer
• Screw Drivers or Powered Drill
• Orbital Sander and Sand Paper
• Paint Brush
• Small Angle Grinder
• Metal Cut-off Disc
• Metal File
• Welder

We initially met with our client's physical therapist to learn more about our client's mobility limitations as well as previous modifications on the bike they had tried in the past.

We then met with our client and the PT together to get a better idea of how she is able to use her bicycle. This helped us understand what problems needed to be solved in order to allow her to use the bicycle independently.

There were two main problems: mounting and dismounting the bike and getting her right foot onto the pedal.

• When mounting the bike, she would have to raise her right leg over the rear tire while holding onto a cabinet with her left hand. She would then have to try and slide her foot onto the pedal. Her right foot tends to point downwards unless she is applying pressure to it, which made this process very difficult.
• To dismount from the bicycle, she would have to swing her left leg over the top bar of the bicycle while being assisted by someone on her right side.

Her goal was to mount and dismount the bike independently and to have a way to keep her foot in the pedal while riding.

Our team started thinking about potential ways to adapt the bicycle. For her to get on and off the bike with ease, initial designs like a swivel seat and a wrap around platform were considered. Having a swivel seat would allow her to have multiple points of contact when getting on and off the bicycle, but this would mean that she would have to tuck one of her legs over the top bar as the seat swivels into position. A wrap around platform would provide her with elevation when she swings her leg over the back tire of the bicycle, however, it would not provide any additional support when getting off of the bicycle.

It became clear to us, at this point, that possibly removing the top bar of the bicycle would provide her with a much easier mounting and dismounting option. We designed a metal bracket that would attach to mounting holes previously used for a water bottle holder, in between the handle bars and the seat. When cutting off the top bar, the bicycle structure will not be as rigid. The bracket would help account for that change, and it would also provide a 10 inch drop from the existing top bar of the bicycle.

To solve the issue of her getting and keeping her right foot on the pedal, we needed a design that allowed her foot to easily get in and out of while still holding her foot secure while pedaling. Our design ended up consisting of two parts. The first being a 3D printed box which slotted right on top of the existing bike pedal. This box provides a larger landing area for her foot than the regular pedal and prevents her foot from falling off the side of the pedal, which was an issue she was experiencing in the past. Additionally, the box serves as a guide for her foot to slide into the second part of our design, which is a conventional toe clip. This toe clip prevents her foot from slipping out the front of the box structure and allows her to actually pedal the bike. The clip is strapped to the pedal itself and wraps around the top of the box.

In addition to the boot itself, we also needed a way to keep it in one place when getting her foot in and out. We went through a couple different designs but ended up going with what we called a heel design. This was a piece that extruded out from the bottom of the boot, much like the heel on a high heel. This extrusion stopped the rotation of the pedal as it wedged itself into the ground when trying to pedal backwards at the bottom of the rotation. Additionally, it held the boot in a position that was easy for her to get her foot into and out of when needed.

Once designs had been chosen, the prototyping process could begin. Before making any actual modifications to the bicycle, we wanted to insure that the bracket design would work. To do this, we made a 3D print of the bracket. Using the CatiaV5 model and downloading it as an stl file, it could be loaded onto a slicer for 3D printers. We chose to have 10% infill with supports since it would just be used for demonstration purposes.

Thanks to a family member, we were also able to get a test bicycle to perform all of the desired design processes on. The main concern that we wanted to practice was the cutting of the top bar of the bicycle. Using a grinder with a cutter wheel, we were able to cut of the top bar at the handle bar and seat attachment areas. This also helped give us an idea of how much the structural integrity of the bicycle would be affected by the removal of the top bar. The test bicycle showed little signs of reduced structural integrity after the top bar was moved. There was some slight flex in the test bicycle, but our prototyped bracket was able to remove all of the flexion after it was put in place. This gave us confidence that removing the top bar of her bicycle and replacing it with the designed bracket, would not compromise the structure of her bicycle.

We went through several iterations of designs to solve the pedal issue. Initially, we were going with a design that closer resembled a walking boot used when someone breaks their foot, only with the front completely open. This supported her foot in the same way our final box design does, but also included supports up her ankle for added security. Our first prototype of this boot design was a simple design constructed out of cardboard. This was just for a proof of concept and allowed us to see if she was able to slide her foot into something like that. We then made a more refined design of this idea that consisted of a box she would slide her foot into (very similar to our final box design) as well as a clasp that her ankle slide into to hold her more securely in. This clasp closely resembled the hand of a Lego minifigure and was connected to the bottom box via a metal bracket.

After coming up with design ideas and prototypes of these ideas, we were able to meet with our client and her PT again to get feedback. We presented her with the test bicycle, new prototypes, and the design drawings of the wrap around platform.

Feedback:

• She was able to do some preliminary testing with the test bicycle, and was able to get on and off of it much easier than with her bicycle.
• She also liked the idea of adding the bracket in the existing holes that previously were used for a water bottle holder. That way the structure of her bicycle did not have to change, and we also did not have to make any other changes to her bicycle to accommodate the bracket.
• When getting feedback on the wrap around platform, her PT had told us that the wrap around platform was considered previously but would interfere with the stand that her bicycle was attached to. Because of this, making longer step stools was proposed. This would provide her with better foundations to stand on, while also avoiding having to deal with the bicycle mount. It was decided to then make her step stools that were twice as long as the ones that she would typically use.
• When testing the pedal design consisting of the box and ankle clasp, we ran into an issue where her foot kept sliding out of the front of the box when starting to pedal. This told us we needed to incorporate something in the front of the design to prevent that sliding motion. At this point, we got rid of the ankle clasp idea and switched to the front toe cap, which ended up in our final design.

Once we proposed our design ideas and got feedback, we were able to take her bicycle to our school lab. This way we would be able to take more accurate measurements, make modifications, and test those modifications.

Once the designs had been finalized, fabrication could take place. The first steps were to mark and cutout the sides and tops of the step stools. Two step stools were made and each has a 12 x 24 inch top, two 11 x 23 inch sides, and three 8 x 11 inch ends. One of these ends is added to the center of each stool to provide extra support. Using 1 inch wood screws, the two 11 x 23 inch sides and two 8 x 11 inch ends were attached together to form the base rectangle. Then the 12 x 24 inch tops were added to each stool as well as an 8 x 11 inch end at the center. After fastening the step stools together, gaps and joints were filled with wood glue to further secure the pieces together. Once the glue had dried, it was time to paint. We used white, outdoor paint since these would be taking some light wear and tear from use. Using a 2 inch brush, two coats of paint were put on which resulted in a complete cover. A concern for us was the slippage of the step stools when she would use them. Since they sit on a hardwood floor, it was decided to put strips of non-slip rubber on the bottom of each stool to prevent them from sliding when they are being used.

After the step stools were complete, our focus moved to the shifting of the top bar of the bicycle. We wanted to fabricate and install the bracket before the top bar was cut to insure the bike would not be deformed. To get the bracket pieces cut, we were able to convert our engineering drawing of our bracket into a dwg file. This was then put into a plasma cutter software and cut out of our carbon steel sheet. After it was cut out, the edges were deburred and the pieces were welded together to form our completed bracket. This was then sanded, primed, and painted white to math the bicycle accents and the other fabricated items. Once the bracket was finished, it was attached and the top bar could be cut. Similarly to the test bicycle, we were able to use a grinder with a cutter wheel to remove the top bar of her bicycle. We decided to cut off the top bar close to both attachment points and cap off the parts of the bar that were left. This way the bicycle would not have to be repainted in the areas where the grinder cut of the top bar, and also to make sure that there were no sharp edges. These caps were 3D printed in a similar fashion as our prototyped bracket, and were sanded and glued the the leftover ends of the top bar.

The final pedal design consisted of three main parts: the box, heel, and toe cap. The box and heel parts were 3D printed using PLA filament and a Bambu 3D printer. The design of the box incorporated a slot in the bottom where the actual pedal would slide into. There were additional spaces on either side of the pedal slot where nuts and bolts could be used to secure the pedal to the box. There were already holes in the pedal from where reflectors were previously attached. These already existing holes provided convenient mounting points. The toe cap was strapped to the pedal and hot glued in a couple places for added security. The heel was glued into the bottom of the box using plastics bonder. Non-slip rubber (the same used with the step stools) was added to the bottom of the heel to prevent scratching the floor and add more traction. This was all able to attach to the bike normally since we were using the bike's actual pedal in the design.

With our modifications to the bicycle, our client was able to mount and dismount her bicycle easily and independently. Additionally, she was able to get her foot into our pedal design and keep it in while pedaling. This allowed her to ride her bike closer to how she did prior to her stroke. She was very pleased with our designs and was now able to do something she loves more easily.