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Friday, January 23, 2009

Motor Tests, Mounted on CrazyBike v2.0

First some full-bike pics of the frame with wheels (no seat or bars), with the motor and some sprockets/etc mounted, to give an idea of size. Front and back are both 24" wheels.

Pics are at twilight, so the camera did some funky stuff with the auto settings again, even though the flash was on for both pics.

I did a bit of digging and found a bent up rear wheel that I could pull the hub out of, to use for the belt-to-chain transfer freewheel device, in place of the orange one in the last post. Still using the same freewheel and axle and bearings, just changing the hub for a couple of reasons. First was because the orange hub still had the remnants of the JBWelded-on sprockets, which would take time and care to remove. Second was that the orang hub is a larger diameter core, whereas the hub out of the bent wheel is a very small diameter, not much bigger than the axle bolt itself. This saves a little weight, but mostly it gives me more clearance for anything that might have to go near the hub (between the frames).

I wanted to use the 14tooth sprocket from one of the cassettes, but neither that nor the 16tooth sprocket were large enough inside diameter to clear the spoke holes on the hub, which are what I need to use to clamp the sprocket down (using small screws and nuts salvaged from one of the ex-10BT racks that contributed to the most recent cargo pod/rack unit). So I had to use the 18tooth sprocket, which means I won't get as good a reduction ratio from that to the rear transfer sprocket, which is a 50-tooth at the moment (largest I can fit without problems hitting the 18 tooth sprocket itself).

The serpentine-style belt from the treadmill that I'm using for the first motor reduction stage is about 3.3:1, taking the ~2100RPM @36V and reducing it to ~636RPM. If I could get a 7:1 reduction to take that to ~90RPM, it'd be ideal. With 24V, I get about 1400RPM, reduced to 424RPM, which would only need about 4.7:1 reduction to get to 90RPM.

Because of noise and such, what I'd ideally like to do is use a belt from one to the other,
or failing that, a much smaller chain type, like that from the old electric scooter, or from a scrapped exercycle-type machine I got from Mark, but I don't have any low-tooth sprockets for that kind that will fit on the hub--the largest of the two I have is barely big enough to fit over the axle bolt, and the smaller (from the scooter motor) is too small even for that, perhaps a tad over 1/4" center hole diameter. That only leaves the two very large sprockets, one of which is over 6" in diameter and the other is around 9 or 10" in diameter. There's nowhere to put both of them, which I'd have to do--the smaller on the motor side, and the larger on the crank/wheel side. If I could somehow fit one of the smaller sprockets on the motor-side hub, then I could get about 7 or 8 to 1 ratio using the smaller of the two large sprockets on the wheel-side of things. That would actually be just about right with max output on a 36volt system to get about 90ish RPM at the crank/wheel end of the motor drivetrain, to match my approximate pedalling cadence. Then that would be processed thru the regular shifting drivetrain just like my pedalling is, to drive the rear wheel at whatever speeds.

I have no other belts that will work, or pulleys, with the right ratios, though I could get about 3:1 using the two serpentine-belt pulleys I took off the Ford a few days ago. I just don't have a belt I could use on those pulleys. I do have a number of V-belts, and some pulleys, but the pulleys are all about the same size, and so useless for any reduction work. I suppose I could lathe a very small one just for the hub end, but V-belts slip when wet, and this system is going to get wet.

So I am using regular bike sprockets, since I do have those in sizes that will fit the shafts I have to use, even though they're not the ideal ratios. It might work out better that way, since it means I will not run at full throttle to get equivalent motor power to my pedalling, so I will have that reserve of 1/3 to 1/2 of full power for emergency speed should it be required (I hope not!).

Anyhow, after reassembling that hub into the device, I mounted it in the Magna frame's dropouts as it will be used. Then I attached the treadmill motor as described in the last post, and adjusted the belt tension via sliding the motor forward and tightening all four radiator hose clamps (which came from the heater hose on the '85 Ford LTD). It holds very well, and does not move when I try to grab it and wiggle it around.

This is the motor and the device with receiver pulley and 18tooth sender sprocket, from right and left sides, with belt installed and tensioned. The frame is laying on it's side, with a spacer between the Magna frame and the Roadmaster frame to hold them about where they will need to be for clearance of the hub. Some later pictures I took show this is insufficient, and you'll see how little clearance there is for the rear-frame sprockets and chain.

More pics of the mounted motor and device, from the front/sides and rear/sides

These show the sprocket alignment between the motor's belt-to-sprocket device and the rear transfer sprocket.

Here you can see I had to increase the spacing betwen the two frames to ensure the very large rear sprockets clear everything on the device. I wish I could use smaller sprockets here, but the ratios I need preclude that on the left side (orange sprocket), and while I could probably use smaller sprockets on the right side (I won't need great speed from this bike, just a lot of pulling power), I don't actually have a smaller three-sprocket set that will work on the one-piece type crankshafts, which is what I used (with cranks cut off) for this.

The black set is the one that will share chain with the rear wheel cassette, actually taking the power transferred by all the previous stages and driving the wheel.

The orange one will take the motor power and transfer it to the black set. There will be another sprocket on the outer end of the shaft there, for receiving the pedal power and transferring it to the black set, but I have to first chuck up the crankshaft in the lathe and drill a hole down the center to tap thread into, to be able to bolt it on. I might end up doing a tackweld on both chainrings on that side, to keep them from loosening with use, as there is no retaining pin to prevent that (unlike on the right side), and the shaft is round unlike removable-crank shafts , so nothing to grab to. I might be able to just flatten or square the shaft instead, and bolt a squared-hole plate to each sprocket, but given the low surface area of the edge against that flat I'm not sure how durable that would be.

Now, it's been a while since I last had a video for you, so here are three!

The first is of the 24 volt power test, using two of the three car batteries:

There's no narration, because I forgot to say anything on any of the videos. ;) They all sound a lot louder than they really are, because the camera has a non-disableable automatic level control that loudens up all quiet sounds and quiets all loud sounds, and there weren't any really loud sounds so the camera basically turned up the volume on everything. Pardon all the neighborhood sounds. You can hear the fan noise, and compare it to the 3rd video at 36 volts, where it changes pitch as well as volume level, to something that sounds more like a familiar sound from under the car hood. :-) But considering that you can clearly hear bird sounds from a distance away mixed in with the motor sounds, the motor isn't really all that loud.

I have some ideas for quieting it down, though. I think some of the mechanical noise is vibration from a problem in the freewheel itself, and I will need to check the other freewheels I have to see if they do it too, or if it's just this one being damaged or worn causing it. When I enclose the fan blades in a guard, I will probably line it with something that should help absorb noise, like the liner under the carpet in the Ford. I'm not aiming for silent, but I do want it to be quieter than my previous setup, which was not very (surprising given that it was rubber rollers directly transferring to the wheel, but then again the motors were very noisy on their own, unlike this one).

This is a torque test for the 24 volt speed. I just took a 2x2 soft pine board and slowly fed it into the 18 tooth chainwheel, from a direction that wouldn't kick it back at me.

The idea was to see how much drag I could put on it like this before the motor stalled. Well, I couldn't stall it at all--it just chewed thru the wood, even if I crammed it between the sprocket and the frame. Slowed it down a lot, as you see, but never stopped. Current draw spiked from about 2 amps unloaded to 6 amps, on up to a bit over 8 amps when I had it between the sprocket and frame. :-) Since it's a 21-amp-capable motor, I don't think I have to worry about overloading it just yet.

The good news is that if it will put out this much torque at 24V, I may not even need the 36V setup at all, which is good because it means I can get away with less batteries. It might even work for just me (no cargo) on the flats with just 12V. I have not done a 12V torque test yet, but I expect I could probably stall it on that, at only 1/10 of it's rated operating voltage.

If it works at 12V, then I can actually run it off of one car battery for what would likely be quite a distance. Or I could parallel the SLAs I have and get more range out of them, but I still don't think they'll last more than a few minutes, at best, and probably not even that, due to their age.

This is a 36 volt test, no load, no torque test. If it doesn't stop at 24 volts, it isn't going to at 36!

As expected, it was noisier, but not intolerably so. I am almost afraid to see how it works at higher voltages, even given that it was designed to run at 120VDC, for 7000RPM total, including the belt and pulleys I'm using on it (which came from the treadmill with it).


  1. What are the two blue wires on the treadmill motor used for?

  2. Jason said..."What are the two blue wires on the treadmill motor used for?"

    They are for a thermal cutoff sensor in the treadmill, though I wasn't really planning to use them on the bike, because I'd've had to build a reader circuit for it to then cutoff the controller when it got too hot, which I would not expect to happen as I was not going to run it anywhere near it's limits.

    I actualy ended up using a powerchair motor instead, though someday I want to go back and try this treadmill motor and another one I have, just to see if the whole idea would work on the road, since it did on the "bench".

    The powerchair motor was so torquey that I could and did destroy chainrings and chains whenever misalignment occured, which due to frame twisting due to some poor design choices happened often.

    I ended up nowadays with a hubmotor in the front wheel, though I havea new bike in progress that will use a motor (not sure which one yet) to drive thru the chain to the rear wheel, with the pedals, as this version would have.

    More info on the two running bikes I have now, plus one in progress, is over here on the Endless Sphere ebike forums (where most of my new information is at). You will have to copy and paste each half of the two-line URL into the browser's URL bar, because blogger won't work properly with links in the comments like this now:

  3. I've mounted a 130V 18amp treadmill motor onto my HP Velotechnik Spirit Recumbent bike. I've removed the pedal sproket and mounted it onto my treadmill motor. I rerouted the chain creating a new connection between the motor and the rear wheel. I mounted the batteries on the rear rack in a weather proof lunch box and wired an on/off switch to the handle bar. I wired four 12volt batteries with 10amps in series creating 48volts, but the motor is burning out. I've isolated the burnout to the magnet wires that connect the two positive and negative magnets to the red and black 16 gauge wire. I'm thinking if I increase the magnet wire to 16gauge and solder it to the 16gauge red and black positive and negative wires I might be able to operate off of 48volts. Do you have any other suggestions?

  4. Well, the first issue is that you're going to need a lot more reduction than what you have, because taht motor is designed to run really fast and be geared down a lot to have the power it does. If you look thru my treadmill motor experiment, you'll find I had to use a two stage reduction before going to the pedal crank, with a total minimum reduction of at least 30:1.

    I did it by using the original treadmill poly-v belt and pulleys, then a jackshaft with #25 (scooter) chain and chainrings, to a final jackshaft that mixed both pedal and motor output into the actual rear wheel drivetrain (complete drivetrain from bike including shifters).

    It can be done less complexly, but I just used what I had, isntead of buying new stuff for it. You could go all new parts and work out a reduction for it that would be sufficient in a single stage, probably, if you have enough room for the very large pulley or chainring you'd need on the drivetrain input and can fit a very tiny pulley or chainring on the motor.

    The next stuff assumes your motor is a brushed DC permanent magnet motor. If it is a brushless motor, then only some of it applies. If it is a brushed universal motor without magnets, then it also all applies.

    What is almost certainly happening to your motor is that there is too much load on the motor, so it cannot reach a high enough speed to have enough back EMF (BEMF) to keep current draw low enough to survive. So the current is so high that it is overheating the motor, causing the windings to smoke (which will eventually burn them out or short them).

    Also, these motors are meant to be fan-cooled, by a fan mounted on the shaft itself, which at low speeds does not move enough air. I replaced my motor's fan with one from an alternator, which moves a lot more air than the original, but still only does any real cooling at high motor speeds.

    Regarding Amps and current limits: Your 12V batteries might be marked as 10Ah, but that only means their capacity is 10A for one hour, in theory (really much much less than that), but they are by no means limited to 10A output. They can easily produce over a hundred amps for short bursts, and dozens of amps for a short time before they are themselves damaged in turn.

    If you had a controller to run the motor, you could both limit the current to it and control the voltage to it so it is not being hit so hard at startup from a stop (right now I assume you're going direct from batteries to motor, which always gives it full power?)

    If you put bigger magnet wire in it might increase it's current capacity a little bit, but it isn't going to solve the problem. You'd have to completely rewind the motor so that it runs much slower per volt that you give it (called kV, usually, basically RPM per Volt), and when you do that the motor will now be a much lower power unit, capable of much less work.

    What I would recommend is to come over to and create a thread for your project, with pics and descriptions of what you have and what you want to achieve, and there are a lot of us that will be able to give you input, to help you figure out the best solution.

    You can find me there as Amberwolf, including the further evolution of my various projects (which I have been posting there rather than here due to lack of time, mostly).


Alternate suggestions or improvements to anything that's been posted is very welcome, and extreme detail is preferred to brevity.

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