PowerChair Motor Installed And Working

After the battery fairy dropped off those U1 deep-cycle batteries plus a power-wheelchair motor, I was itching to get them on the bike and try them out.

It took a few days before I really had time to do it, and then it took two days to actually get it done, but now I have a motorized bike capable of about 15MPH under motor power alone, and up to 20MPH with pedalling. It could actually go a lot faster than that, perhaps 30MPH or more, but A) that's illegal here in AZ and B) it's not geared right to get that fast (on a flat road).

This is what it look like as of just before I went to bed last night (well, actually this morning around 6am, but I didn't realize it was that "late" until I got to bed). I forgot to take a side pic of it as it is right this minute, but the only visible differences are the thumb throttle being added and the pedal-chain tensioner (old derailer) being replaced with a non-bent one.

The front pic above is from just before starting this blog entry, although you can't see it very well because I needed to do these pics outside in daylight, several hours ago, but forgot.

Remember that trip I took in the extreme wind about two and a half weeks ago? I went after some Freecycle items, including bedframe parts.

This derailer hanger isn't made from one of those actual parts, but it is from an old bedframe I'd saved the hardware from, when I moved several years back and couldn't take the whole frame with me. I am not even sure what made me try it, but it fit almost perfectly the first time, and it was the first piece of hardware I grabbed out of the pile of brackets to try for this. Originally I was going to just weld a rear dropout from a scrapped bike onto the new bottom mounting plate, but then used the brackets when I ran across them looking for something else that day.

This is the same parts, from an oblique-ish forward view.

A closeup of the drivetrain section as it is now (though the chain shows slack that isn't really there--it was just caught on one of the bent derailer's edges).

On the left you can see part of a crank on the chrome chainring set. It was from a bike with an apparent crash on that side, which had bent the pedal and damaged the very end of the crank. The rest of the crank was intact, and since I might reuse these parts on another bike later on, especially if I get better parts for this one, I opted not to cut the whole crank off the chainrings (it's swaged on, like most cheap bike chainrings/square-taper cranks). However, since it won't clear the bike frame on the top part of the circle, I did cut off the bent/broken part, just at the edge of where the threads would have started. The crank is so long it can still be re-drilled and re-used as a shorter crank someday.

Before I put the controller and stuff on, it looked like this, with just the empty space above the mounting plate I welded onto the bottom of the Magna's rear triangle.

The drivetrain is different now, in that I now have two much larger chainrings on the right, at the front of the rearwheel drivetrain (the one I can shift gears with). The smallest of them is a couple of teeth larger than the biggest of the three chainrings that used to be there, meaning I can now get more speed, at the sacrifice of low-speed torque. With the motor on there, it hopefully won't be that bad, but really I didn't have a choice, as I had no other parts around I could do this all with.

I had to move the 3-ring set to the left side, replacing the two independent ones I had made for that purpose. I didn't take pics (need to) but the way I made them simply wasn't going to hold up to continued usage. I'm surprised they lasted as long as they did, given what they looked like when I took them off. The square-taper hole I had filed in the metal discs used inside the ex-freewheels the chainrings were mounted on had been notched by the torque on them, and would have eventually (at an unknown time and place) broken right thru, making them round and no longer able to drive the bike. The only reason I used them at all was that I needed the freewheels between the motor and the pedals so they wouldn't drive each other, and the freewheels themselves failed (one was already bad to start with and the other failed pretty quickly, forcing me to weld the freewheeling rings to the core just to be able to ride).

So since I expect that between the motor and the pedals to be increasing the torque applied at that point, I'd better use something with more surface area to transfer that torque. All I had without serious time making my own (possibly weeks of spare time filing) was two chainrings sets with square-taper holes (not counting the one on my upright bike, which has to stay functional). One 2-ring unit with the damaged crank above, and one much smaller 3-ring unit I'd already been using on the righthand (rearwheel) drivetrain of this bike--the orange one below.

Since the smallest chainring (granny ring) was the best match for 1:1 operation with the motor and it's magically-fitting chainring, that left me the middle ring and the largest ring for the pedal chain. Both of those being significantly larger than the pedal chainring at that time (the orange small one two pics up on the righthand side of the bike now), they'd leave me with virtually no speed when on pedals, and my feet flying off the pedals when the motor ran. Plenty of torque, though, I guess. ;)

That left me with needing to change the front chainring, on the pedals, to something larger, preferably something 1:1 with the smaller of those chainrings. I didn't have anything the right size for that that could be mounted on there easily. I had hoped I'd find something that I could just bolt onto the small already-welded-on chainring, but nothing had the same mounting holes, nor any place I could drill them without weakening it too far. There were some that were sort of close, but they'd've been loose and not stayed in position properly, and if it didn't cause the chain to come off it'd still wear thru the bolts holding it on, eventually, and cause a worse disaster out on the road someplace when I'd finally forgotten about the problem. :(

So I did the next best thing: I took the only chainring I had off a one-piece-cranks bike that would let me later change the chainring itself if I had to (it's held on with 5 screws), and welded that center spider to the *other* crank (the one originally *intended* to be on the left side of the bike) and flipped the cranks back over. So now I have an unused small chainring on the righthand crank, but it doesn't cause a problem nor add significant weight. It just looks odd.

The chainring just added and the largest of the 3 receivers are about the same number of teeth (I didn't count them yet, as I didn't really have any choices on parts for this section, so it doesn't yet matter). They also line up almost perfectly; well enough to not have the chain come off.

It didn't have a way to tension it, though, as I haven't built the tensioner/throttle for this drivetrain yet (still pondering it), so I put the derailer back on as a tensioner/guide for now, attached to that bedframe piece.

You can also more clearly see the plate welded to the bottom of the Magna's triangle, which has slot-shaped holes in it for the 6 mounting screws in the top of the motor's gearbox, and for the clutch exit/lever mounting point. The clearance for the motor and chainring on the motor's hub was exact, but I miscalculated the chain's thickness, so it rubs lightly on the bottom of the plate. I used shim-type spacers (made of a broken hacksaw blade) between the motor and the plate to try to fix that, but it is not enough, and I'll need to use more shim thickness.

A friend (Mark) was here at the time, and helped me file out some of those motor mounting holes in that plate, while the very stiff cold wind tried to blow us away.


Motor mounting screws I thought would be a problem, but it turns out that modern non-caliper brakes (with studs either side of the wheel for pivots) use screws with the same diameter and thread pitch, and I have a handful of unused ones that quickly filled the bill. They are not long enough for one part of the moutning, so they only grab a few threads there, but the other side is fine. Hopefully I'll run across longer screws in something I'm repurposing, before there are any problems.

This is the clutch for the motor's gearbox. It's that small lever pointed off to the left, in the bottom center of the pic.

If I have to use that for any length of time, without being able to figure out and install a freewheel, I'll be putting a thumb-style shifter lever on my handlebars for it, to pull it open when I need to disengage the motor (as that's only easily done at certain points in the gear revolution cycles inside the gearbox). I'd rather just use a freewheeling setup, but that is going to take time to figure out exactly how to do it with the parts I already have.

I do have some ideas, one of which is essentially the same as the belt-to-chain power transfer device I'd made for the treadmill motor, which included a freewheel on the belt pulley mount. That only gives me a freewheel for the motor, though, and still leaves me with pedals being pushed by the motor.



One more thing I needed to do for the batteries was add the rightside cargo pod, which I've been putting off because I really didn't want to cut a hole in it just to clear the derailer. I thought of this crazy temporary solution and tried it:

It's just a block of 1x1 scrap held to the chainstay by a radiator hose clamp. There are also two screws deeply in it from inside the cargo pod, to secure them together and keep the wood from rolling down under the stay, which might make it catch the rear wheel spokes or chainrings. That's generally very bad when movng, so I try to be sure and pass on any chances of that happening.
Before adding the pod itself, here's the wood.

One other thing it does is adds side clearance for the bike kickstand, the purple foot of which you can see right below the wood.

Attaching it is done the same as the other pod. Three radiator hose clamps around the tubing behind it, which are at different angles and thus prevent the pod from sliding around.

I'd rather have a frame just for holding these on, but that bike is still in planning stages, and may not be even started for months.

Hard to see, but this is the clamps on the bike frame itself.

The side panel of the box, with tape covering the vent holes.

Eventually I'll find a full sheet of aluminum to replace it with, thick enough to help with loads and anti-theft of pod contents, but till then they'll do.

Looking down into the new box, you can see the battery (covered for safety by it's original cardboard cover, so nothing can get in and short the terminals) My toolbag fits in there, too.

Unfortunatley I don't have a lid for it et, so no lock either.

Then the old box, with the other battery in it, and some assorted stuff, and the gray battery charger bolted onto the side.


I don't have another small pot of the right value range to try the same in-the-handlebars trick I did with the upright, to make my own grip-throttle again.

So instead I used a 5K pot of standard panel-mount pot. That fit with very little filing into the seat-post-clamp hole of an L-bracket for a seatpost-mounted-reflector. One of the reflector mounting holes is used to run the rear derailer lever's main bolt thru, which doesn't affect it's operation.

So now I have a good thumb throttle. By the way, this also fixed the problem I had with never getting more than roughtly 2/3 of the battery voltage at the motor (not full duty-cycle PWM).

WIth this,it goes from about 3.09 v (of 10V) at the throttle's output giving roughly 1/2 motor speed, to 3.1V, where it gives full motor speed. There is no fine control for those, and I think it is because this was originally on a hall effect sensor, with a magnet in a twist-grip throttle.

I decided to change out the little scooter horn (middle) for a car horn (from the Ford LTD).

It was quick and easy, though it uses the frame of the bike fro ground, so can' be powered easily from the main battery, and has me using a separate small SLA for the scooter-based lights, horn, etc. The LED lights are all on one of the motor batteries.

Here's the bike computer after a bit of riding around the neighborhood with the motor running, to test things out.


A closer shot of the controller area, from above. The rear bolts holding on the motor are visible at the left edge of the metal plate in the pic. I'm considering bolting the heatsink to the bike tube framing, as it will not fit on the flat areas down there.

More stuff and pics in a future post, after more test riding.