3D model description
This is the retractable docking pin that I designed to dock my Frontier wheelchair in my van. I need a docking pin that retracts because the fixed docking pins kill the ground clearance and hit the ground and door thresholds. Now I can go offroad over rocks without worry.
It uses a small actuator with a 2" stroke to extend or retract a 8 inch bolt through a round tube. I designed brackets to be 3d printed for mounting the actuator. Dad welded the steel tube to the angle and I 3d printed the brackets. The bolt locks into an EZ Lock or QLK docking system.
The cost of the parts and materials for this retractable docking pin was just $127, which was several thousand dollars cheaper than what the wheelchair company was charging.
This docking pin was designed for the Frontier V6 power wheelchair by Magic Mobility but it can be adapted to fit other chairs.
Retractable Docking Pin Parts List
Description Qty Vendor Cost Link
F12 Micro Linear Actuator 2β Stroke 1 Firgelli Automations $69.95
https://www.firgelliauto.com/products/f12-micro-linear-actuators?variant=39574554116167
Steel Round Tube, 0.12" Wall Thickness, 7/8" OD 1 McMaster Carr $6.07
https://www.mcmaster.com/7767T45-7767T451/
Steel Hex Head Screw, 5/8"-11 Thread Size, 8" Long 1 McMaster Carr $7.67
https://www.mcmaster.com/91257A822/
Steel Hex Nuts, 5/8"-11 Thread Size 2 McMaster Carr $5.22
https://www.mcmaster.com/98797A535/
Steel 90 Degree Angle 1/8" Wall Thickness, 1-1/2" x 1-1/2" 7β McMaster Carr $5.62
https://www.mcmaster.com/9017K484-9017K481/
Steel Bar, 1/8" Thick, 1-1/2" Width 6β McMaster Carr $3.08
https://www.mcmaster.com/8910K398-9143K316/
Clevis Pin 1/8" Diameter, 1-1/16" Usable Length 2 McMaster Carr $8.28
https://www.mcmaster.com/92390A095/
Waterproof Momentary Polarity Reversing Rocker Switch 1 Amazon $10.29
https://www.amazon.com/dp/B08MZ65Z3F
100 Ohm 5 Watt Resistors 2 Digikey $1.30
https://www.digikey.com/en/products/detail/te-connectivity-passive-product/EP5WS100RJ/4489281
Lower Actuator Bracket 1 3d Print from Cults $6.00
https://cults3d.com/en/3d-model/various/retractable-docking-pin
Upper Actuator Bracket 1 3d Print from Cults $1.00
Switch mount bracket 1 3d Print from Cults $1.00
Inline Fuse Holder with 2 Amp Mini Fuse 1 $2.00
Total: $127.48
Assembly Instructions:
Cut the steel tube to 4.5 inches in length. Weld the steel tube to the angle. Attach the F12 Micro Actuator with 3d printed brackets. Use 5/16" or M8 hardware to bolt the docking pin to the battery box.
The wheelchair batteries are 24 volt and the actuator runs off 12 volts so I used 100 ohm resistors to reduce the voltage. I picked resistor values that match the motor impedance, which cuts the voltage in half. I used resistors instead of a DC converter because the DC converters constantly draw a quiescent current which will drain the battery over time. By putting the resistors on the load side of the switch, there is no quiescent current.
This design is for informative and inspirational purposes only.