Accessible Gym Board Scooter

For a school project, my team was challenged with designing and manufacturing a board scooter for a child with cerebral palsy entering kindergarten. This allows them to participate in gym class, and will help them develop their motor skills.

Materials

1. Testa Seat
2. Wood sheet 20 x 20 x 1/2" (We used plywood, but we found that's prone to splintering, if budget allows perhaps consider MDF, which will look nicer when finished)
3. Hardware
4. 16 x 1/4-20 Countersunk bolts (8 x 1.5", 8 x 2")
5. 16 x 1/4-20 Nylon locking bolts
6. 4 x #10-24 Countersunk bolts
7. 4 x #10-24 Nylon locking bolts
8. 4 x Large washer for #10 bolt
9. Metal L-bracket
10. Spray paint
11. Primer
12. Paint
13. Clear coat

Tools

1. Drill or Drill press
2. Panel saw or Table saw (if wood stock is large), otherwise a Band saw is fine
3. Scroll Saw
4. Router table
5. Belt sander

The Testa-Seat is the crown jewel of this product. It is a custom sized seat with a 4-point harness to comfortably hold onto the child using the scooter. Ordering this seat requires a number of physical dimensions of the child, the most up-to-date ordering guide will be found on their website. At the time of building we needed the dimensions seen in the picture above. We chose to oversize our seat since the scooter was not going to be used regularly for a few months.

The first step done was cutting the wood to size. In our case, we chose 20 x 20", which is 8" wider than the seat. This gives the scooter a firm base for the seat to sit on, preventing it from tipping. Our stock came as a 4 x 8' sheet, so this was done with a panel saw.

After cutting the piece to size and verifying it was square, a router was used to cut a slight chamfer on the corners. Additionally, the corners of the board were sanded down to a corner radius of around 1".

The next step was marking the holes for the caster wheels. We measured this by hand, however I'd suggest creating a template to be as precise as possible (our boltholes were not perfect, and it was hard to get the plate flat until the bolts were fully tightened). These holes need to countersunk, so a countersink bit is needed. It's possible to use a bit designed to cut the countersink and the hole at once, or a bit that cuts the countersink after the central hole is drilled. Make sure the countersink bit has quite a few flutes to prevent the result from looking hexagonal.

After cutting the caster wheel holes it is necessary to cut the seat mounting holes. To do this we measured the front to back length of the seat. After doing this the holes were marked to place the base of the bracket under the seat. Because the holes in our brackets were not inline we accidentally drilled some extra holes which would have put our countersinks on the wrong side. Be careful to check this before drilling, or drill these holes prior to countersinking the caster holes.

The final modification to the board is cutting slots for the straps of the seat to go through. The brackets were temporarily fixed in place, so the seat could be positioned in place. Then the board was marked where slots needed to be cut. Each slot was cut by drilling a properly sized hole on either end, and cutting a straight line to connect the holes with a scroll saw. Originally the two slots on the sides of the seat were too small so we slightly enlarged them with a sanding wheel on a dremel.

With this done the Seat was ready to be painted.

When we visited the hardware store, we were unable to find hardware that matched the size and diameter of the mounting holes on the Testa-Seat. Because of this, it was necessary to drill the mounting brackets.

To drill the brackets, they were temporarily mounted in place and visually marked to be in the same spot as the mounting holes on the seat. Then each bracket was placed in a bench clamp, and drilled out. The mounting holes on the Testa-Seat were measured to be approximately 5/16" for a clearance fit. This is a decently large hole to drill in steel so a pilot hole (1/8") was drilled first.

We chose to paint our board with spray paint. Precaution should be taken when spray-painting, such as using an N95 mask, or a respirator, and disposable gloves. Additionally, you should never spray paint in a closed poorly ventilated space.

We started with two coats of white spray primer. This was to seal the board, so the board would accept more color without absorbing too much paint. Then two coats of colored paint were added. This was finished with two coats of enamel protective coating.

The assembly of the final product was very straightforward.

First, the four caster wheels were bolted to the plate (1/4-20). Each caster had four bolts which were held with a nylon locking nut.

Next the L-brackets were bolted to the plate (#10-24). To prevent the nut from squeezing the board, a large washer was placed between the board and the nut.

Now the seat could be attached to the board. The side straps were fed through the board, and the front thumbscrew was fastened. The rear bracket is designed to be attached to the seat, and the counter-balance plate, so that had to be put in place prior to bolting. This counter-balance plate was also velcro strapped into place.

With that the assembly was complete!

After trying out our initial design, the physical therapist we were working with asked if it would be possible to increase the height slightly, as well as add a mild inclination angle. This was done by adding spacer plates under each caster wheel cut from the excess plywood. Since the plywood was 1/2" thick, we placed one layer of spacers in the rear, and two layers in the front. This added around 1.5 degrees of recline.