Introduction: PPAT Team Erik
Erik is an awesome man in his 40’s. He is paralyzed from just above the waist down from a motorcycle accident at age 19 and uses a manual wheelchair. He enjoys “Wheelchairboarding” (longboarding, landboarding, hover-boarding, etc. with his wheelchair), a sport he created. Erik uses a specially modified board to distribute the weight of the chair to allow ease of balancing. Erik likes to mount his board by building enough speed to hit the board and jump up onto it (similar to a bike jumping a curb). However, environmental factors such as the roughness of the ground, height of the board, and the availability of a curb can affect his ability to mount and maintain the balance needed for boarding, limiting the types of boards Erik was able to purchase and use. Erik recently designed a new landboard for himself, but it is taller and thus more difficult for him to mount. We designed a mechanically raised mounting assist to lower the impact height of the board and make it easier for him to mount in any condition.
Bill of Materials
- 1"x3"x6" Aluminum Block (McMaster-Carr 8975K239)
- ~420cc of Markforged Onyx Filament (F-MF-0001 for 800cc)
- 10x 1/2" 10-24 Screws* (McMaster-Carr 91772a242)
- 10x 10-24 Locknuts* (McMaster-Carr 91831a011)
- Loctite (any version of Loctite Threadlocker should work)
- 3 ft. 1/2" Diameter Steel Shaft (McMaster-Carr 8920K155)
- Need enough for 2x 7.5" length shafts
- 4x Set Screw Shaft Collar for 1/2" Diameter (McMaster-Carr 9946K15)
3ft. long 1.5" High** Aluminum L-bracket 1/8th" thickenss (McMaster-Carr 8982K13)
- 3M Safety Walk Slip Resistant Tape
*Screw size and thread count can be altered as long as the locknuts and screws are the same size and thread count and the holes are adjusted on the aluminum mounting plate.
**The height of the L-bracket needed is dependent on the height of the L-bracket's in use on the other side of the board, the height the aluminum mounting plates extend above the bracket, and the thickness of the board. These can be adjusted as needed.
- Markforged Composite Printer
- Any of their printers capable of composite printing Onyx will work
- Markforged's Eiger software
- Solidworks 2018
- If you are using a different version of CAD software, you can find Step versions of every file to download here.
- Drill Press
- Band Saw
- Disk Sander
- Arbor Press
**All necessary files for this project may be found at https://github.com/lyndiem/PPATTeamErik/tree/master/FilesForInstructable/STEP%20Files%20For%20Documentation **
Step 1: The Hinged Wedge
The hinged wedge is the main portion of the assistive mounting device and is designed to lower the impact point of the wheelchair wheels so Erik has an easier time mounting the board (the required force scales non-linearly with the height from the ground). The shaft hole is designed to be a press fit so the shaft rotates through the aluminum mounting plates rather than the hinged wedge.
This part was 3D printed in Onyx (a Nylon-Carbon Fiber composite plastic) for it's high strength to weight ratio. The X-patterns in the wedge portions are designed to provide structural reinforcement while reducing overall weight and material usage.
The STL file was assembled in Markforged's Eiger software and printed on a Markforged Composite Printer. One hinged wedge was printed for each end of the board. The print time for each hinged wedge is approximately 1 day and 22 hours.
A strip of 3M Safety Walk Slip Resistant Tape was then measured to match the length of each ramp portion, cut, and stuck to the top of the wedge for extra traction in wet conditions.
If no edits need to be made, the attached STL file can be downloaded directly and 3D printed in an appropriately strong material.
The shaft size, height the wedge portion extends below the board (to lower the required force or to adjust for a taller board), angle of the ramp-like portion, width of the ramp-like portion, and length the wedge portion extends from the board can all be adjusted for different board or design requirements. A SLDPRT file is attached that can be used to guide the process. A STEP file can also be found here.
If 3D printing is not possible, the wedge sections of the SLDPRT can be hollowed out in the center to sheet metal thickness, flattened, cut on a waterjet, and bent into shape. A wooden wedge can then be bolted between the edges to strengthen the part.
Step 2: Cutting the Aluminum Mounting Plates
The Aluminum Mounting Plates are used to mount the hinged wedge system to the L-brackets. The hole for the shaft is meant to be a transitional fit to allow the shaft to rotate and raise or lower the hinged wedge, while still providing a small amount of resistance. The helps lock the ramp up while Erik is on the board.
The SLDPRT file was converted to a DXF, uploaded, and cut using a Waterjet.
A drill press was then used to drill the hole for the shaft and the mounting holes for the bolts.
If no modifications need to be made, the DXF can be used directly on a Waterjet, noting that the dimensions were saved to scale in inches. The SLDPRT file is attached if edits need to be made to any of the dimensions. Note that you will need Solidworks 2018 or later to access the file. A STEP file is also available here if you are using other versions of CAD Software. The thicknesses can be adjusted as needed, and the hole diameter can be adjusted to account for different shaft sizes. The hole locations can also be adjusted as needed.
A programmable mill could also be used to cut the mounting plate out.
Step 3: The Shaft
The 1/2" diameter shaft was cut into two 7.5" long shafts using a Band-Saw.
A Disk Sander was then used to smooth the ends for aesthetic and safety reasons.
The diameter, length, and height can all be adjusted according to changes in other parts.
Step 4: Assembly of Components
- Using the Arbor Press, press one 7.5" long shaft through the 1/2" diameter holes in a 3D printed hinged wedge such that the wedge is centered on the shaft (extending 1.5" on both sides).
- Slide one aluminum mounting plate onto each end of the shaft.
- Attach shaft collar outside the aluminum mounting plates on each end of the shaft.
- Tighten the set screws.
- Repeat steps 1-4 for the second hinged wedge.
Step 5: Assembly Onto Board
- Cut 2 L-brackets to 7.5" length
- Measure and drill appropriate holes for mounting each L-bracket to the board
- Place the bottom of the L below the board and align the holes
- Place screws through each hole in the board
Attach a locknut on the end of each screw and loosely tighten (do not fully tighten until all locknuts have been placed).
Apply a drop of Loctite to the threads of each screw.
Tighten the locknut fully and let it dry.
- Align the component assembly to the board so that the aluminum mounting plates rest on the top of the L-brackets and align with the mounting holes.
Drill appropriate holes for mounting the component assembly to the board with the aluminum mounting plates resting on the top of the L-brackets
- Place one screw through each hole of the mounting plates
- Attach a locknut on the end of each screw and loosely tighten (do not fully tighten until both locknuts have been placed).
- Apply a drop of Loctite to the threads of each screw.
- Tighten the locknut fully and let it dry.
- Repeat steps 3-13 for the second hinged wedge.