DIY Retractable Docking Pin for the V6 Demo and Design

[DrewDigital]

Retractable Docking Pin Demo and Design for V6 Frontier Wheelchair on Youtube
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 an 8 inch bolt. 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 design and 3d files can be downloaded from Cults:
https://cults3d.com/en/3d-model/various ... ocking-pin

This docking pin was designed for the Frontier V6 power wheelchair by Magic Mobility, but it can be adapted to fit other chairs. The bolt locks into an EZ Lock or QLK docking system.

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.

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. (They quoted me $4650!)

[Burgerman]

(They quoted me $4650!)

Only in america! Are you sure they got the right number of digits?
Mechanically good.
Beware the resistor. The actuators resistance or rather current draw changes with load and speed. But it should be close and work OK in this application because the load is pretty constant and light. And because under light load a 12V motor will work OK on 24V anyway.

The Current draw on a 10A 24V to 12V inverter was just 6mA on the one I used on my BM3 chair. Around the same as the wheelchair controller itself when turned off. So you still need to top up a battery every 14 days overnight regardless of inverter or not. ALso, you could put the actuator switch to the supply side of the inverter and then no current when not in use.

[ICEUK]

Looks good,well done.

It got me thinking though, could you not run the motor from the r-net ism using a spare channel say "Footplate" and use the joystick to control the actuator rather than a switch.
I believe it's a 12 volt output.

[Burgerman]

You could. The typical ISM has 6 channels. With Tilt, Lift, Recline, and POWER footrests (or centre power footrest with length adjustment) a total of 5 channels are used. Leaving a spare one you can call DOCK or whatever.

Name them whatever you wish. Call a channel DOCKING PIN and then set it to 12V and set to auto sense full retraction or full deployment (endpoint) due to built in current sensing. No electronics required at all, just 2 wires, and 2x 6.3mm spade terminals. And obviously a programmer. Super simple. And you can adjust it the same as an extra seating option.

In programming set to 50% speed UP and DOWN to get a 12V (50% pulsewidth) and set 12A max. The stuff in yellow!
In the visuals and channels set channel 6 and set the UP/DOWN arrow, and call the label DOCKING PIN.
OBVIOUSLY DISABLE NEEDS TO BE SET TO ENABLE HERE! I cocked it up...


And then be sure that the end stop sensor is set to enabled, and set 50 for the timer so as to never damage the actuator ram. Then it will work safely reliably and look right on your screen so you can see what you are doing. If it goes the wrong way swap wires or tick invert direction. Connect the 2 wires to the port marked channel6.

[DrewDigital]

Looking at the load curve for the actuator, it draws 0.08 amps at no load and 0.2 amps at full load. That translates to an impedance range of 150-60 ohms. So I used 75 ohm resistors (2 of them for a combined 150 ohms) and when I measured the voltage across the actuator, I got 15.7v going down and 13.2v going up. That's acceptable, but it should be a little lower, so next time I would use 100 ohm resistors.

The actuator only puts out 5 pounds of force, so it draws very little current. The only downside of resistors is that they waste power, but its only used for a few seconds at a time, so no big deal.

I thought about using the legrest output of the ISM, but then it would add an extra function to the joystick that would be annoying. I use the tilt and elevate a lot, and having to cycle through a third function would be cumbersome. So I decided to keep the docking control separate, because I don't drive often.

My chair has plugs for lights and legrest under the seat pan. So when I wanted to add lights I had to figure out what type plug to use. I got the plug connector and pins on Digikey:
https://www.digikey.com/en/products/det ... -2/1148116
https://www.digikey.com/en/products/det ... -1/1130683

[DrewDigital]

The only downside of my design is that the actuator could be damaged if I hit a rock and it pushes the bolt up. The actuator has gears inside that could be stripped.
I saw the promo video for the Magic Mobility retractable pin, and it looks like they use a solenoid actuator. (because it pops up and down.) That can be pushed up and not cause damage.
When I looked for solenoid actuators, I could only find them with a 1 inch stroke, and I didn't think that was long enough. So I used a linear actuator with a 2" stroke.

[Burgerman]

I did something much less complicated. I mounted the tie down on some 35mm square bars on the vans floor. Meaning it sits 35mm higher. So the bolt can be 35mm shorter on the chair. Thats around 1.5 inches more clearance. Giving 3 inches of bolt/ground clearance on my chairs

So nothing moves or needs to move.

[DrewDigital]

I did that on my old chair. I had two - the X5 and Q6. Dad welded together a low-profile pin for the Q6 and we put the EZ Lock on wood blocks to maximize ground clearance. Then set the pin on the X5 to the same height. The clearance was manageable around town but hit rocks off road.

Once I went to an RV expo and looked at a toy hauler with a ramp on the back. When I rolled up the ramp, the pin dinged the edge of the ramp on a brand new toy hauler! I didn't say anything and the rep didn't notice, but I did ding it.

And if the tires weren't inflated properly, the chair wasn't high enough and would get stuck on the EZ Lock.

Last year I got a new chair (V6) and a new van, so this time I wanted to do something better. And my brother is getting a V6 soon but his insurance won't cover the docking pin, so now that I have the design ironed out, it'll be easy to make one for him.

[Yennek]

The only downside of my design is that the actuator could be damaged if I hit a rock and it pushes the bolt up. The actuator has gears inside that could be stripped.
I saw the promo video for the Magic Mobility retractable pin, and it looks like they use a solenoid actuator. (because it pops up and down.) That can be pushed up and not cause damage.
When I looked for solenoid actuators, I could only find them with a 1 inch stroke, and I didn't think that was long enough. So I used a linear actuator with a 2" stroke.

First off, very cool design. I've often though of doing something similar, thanks for sharing. Question though, what material did you use for your print?

Second, if you are worried about the bolt when down, you could modify the design to account for that pretty easily I would think. If you remove the lower of the two nuts on the pin, then it looks like the pin will be free to slide up and down when the actuator is in the down position. If gravity isn't enough to reliably get the pin to fall when the actuator is lowered, you could add a lightweight spring to the assembly pulling the pin down.

Or if you are just worried about forgetting that it is down, maybe add a microswitch that trips when it is down, and connect it to an inhibit pin on the ISM so you're stuck going slow until you remember retract it.

[ex-Gooserider]

Would it be possible to add a spring in between the actuator and the bolt, so that if the bolt hit anything it would push up and compress the spring before damaging the actuator? The actuator doesn't need to hold the bolt down when in the Ez-lock and if you used a reasonably stiff spring it could still pull the bolt up...

ex-Gooserider

[slomobile]

I like it!
Good job spreading the load and separating the horizontal loads from the vertical actuator.

I'd like something similar, but eliminating the EZ lock base. My van already has L track flooring like yours. I'd like to clip in to that like the Q straint retractors do, but eliminate the straps that take 2 hands near the floor to release.

Maybe like a cane or 2 canes with one of these at the tip https://www.etrailer.com/Tie-Down-Ancho ... PSSTD.html
insert the cane through the tie down loops on the chair and engage to L track. Release by pushing a button at a comfortable height on the cane.

I sleep on the van floor so Im trying to avoid protrusions. Its not worked out yet, thought someone might have an idea.

[ex-Gooserider]

I'd also love to have a protrusion free, easily deployed lock down setup... I use an ez-lock for my chair in the drivers position, but need to get in and out through the center of the van, so it doesn't really work to have any sort of stuff in the tracks on the floor...

But my GF also has mobility issues as well as being legally blind (which sort of rules out her having much of a power chair) Right now we do a seriously kludgey setup where she puts her walker or manual chair behind my chair, and then uses the seat belt from the left passenger center row seats (the seats aren't there but they don't remove the belt) wrapped around to connect to the seat belt anchor that I'm supposed to use for MY seatbellt (I don't use it)... This isn't real secure, but works most of the time... However I wouldn't trust it for a long trip, or with anything heavier than her manual chair... (I also don't think it would actually work if I did have an accident)

However I don't really see any way to add more anchors that *I* could use from my chair (she has trouble finding the ends of the seatbelt and getting them connected) and which wouldn't get in my way getting in and out of the van...

Having a multi-disability household is even more of a headache than just one person....

ex-Gooserider

[slomobile]

GF also has mobility issues as well as being legally blind (which sort of rules out her having much of a power chair)

Some things I'm working on might go slightly toward improving the situation for visually impaired power chair users. I'm far sighted, and the point at which things get blurry moves further away as I age. Currently, things closer than 4-12 ft are blurry without glasses, varying by how dry my eyes are. Wearing glasses screws up my good distance vision and makes me dizzy if I move. Bifocals make me throw up when I try to walk.

Remember the robot following from the front project?

Your chair in front could autonomously give "ques" to her chair about which direction to go. A knob on your chair represents a setting for desired following distance. If her manual chair had 2 power assist wheels (2 direct drive E bike wheels) they could be programmed to give haptic feedback. Assume you are leading and going left but she is falling behind. Her right wheel could vibrate in proportion to the gap between you, signaling her to push harder with the right till the vibration is minimized. Like sonar with the frequency scaled down from supersonic to subsonic/haptic.

There could be several different kinds and strengths of vibration in each wheel so she can gauge how far she is away from you, and from obstacles. If there is a longer pulse width in the reverse direction, it indicates you are either behind her or she has gotten closer than the set following distance. The frequency, amplitude, and duration of pulses could indicate a few things. If the pulses are much stronger in one direction, it will be easier to push the chair in that direction. But she is always in control of where she actually goes, and has her own dial to turn down the que strength, or up to the point of becoming self driving.

A higher pitched range of vibrations could indicate the direction to the largest obstacle around the front of her chair. The sensors could be the same common cheap SRF-04 sonar sensors used in Luci and similar systems. Rather than haptic, that feedback may be preferred audibly by stereo speakers in the headrest.

After using my prone chair for a year now, I often prefer to drag my toes along the ground while riding it. It tells me if I'm on gravel, grass, pavement, carpet. I can feel door frames with my toes and better guide myself through them. I stay centered on the van ramp by feeling the 2" lip at the edges. In tight areas, I put my knees into the pads to get them out of the way and rest my toes near the casters so I can feel which way they are flipping. It really helps when backing up.

I'm working on a powered caster project today that might be able to turn any wheelchair with casters into 4wheel drive. Just a bit more math to deal with avoiding caster fip.

I carry a lightweight aluminum hiking cane similar to a white cane, but green with a handle. I use it to push and hold doors open, pull things toward me, feel for drop offs. If I am on an exam table at the doctor, I'll use the cane handle to push the joystick to drive the chair away at the start, and pull it toward me at the end.

The protrusion free docking hasn't advanced much, but I'm almost certain the cane will be some part of it. We need to position and move some latch at floor level without being at floor level. A stick with a button seems about right. I'll have to learn a bit about how white canes are constructed and used to see if they could be employed to this purpose.

[ex-Gooserider]

I tried a set of those assist wheels a while back and was very unhappy with them in the short demo... There was a definite amount of slop between when you pushed on the rim and the motor kicking in, which ended up feeling like the rims were not giving proper control of the chair...

We would also have issues with the added weight and width, as we already have to partially fold the chair so she can push it up the ramp after I get in when using the van. She also only has about an inch or less clearance getting in our front door... We are trying to replace her currently worn out Tracer IV chair, and they wanted to get her a Quickie M6, but the 26" M6 won't go through our front door, even though the 26" Tracer IV does... (Unfortunately her official weight is about 375lbs, and most of the options for bariatric rehab chairs have a weight limit of 350, so the vendor won't even talk to her about them, as her insurance won't pay for a chair that she is "to heavy" for...)

ex-Gooserider