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Friday, October 30, 2009

Technical Difficulties Mark II; 4-Pole Motor Installed

First, the good news: The 4-pole motor is finally installed and tested as well as expected.

The bad news: today was filled with "technical difficulties":

--Tire has been going flat so something isnt' being plugged by the Slime. Took wheel off and tube out, to find one of the other patches has a split down the middle--poorly made patch, I guess. Glued a new patch from a different brand, waited the requisite time, inflated it to test, and the new patch has a tiny hole in it's exact center, which of course is right over the original hole. Scrubbed that off and put another patch on successfully this time.

--Put wheel back on, reinflated, rode around the block and SPANG! a spoke breaks. :( Not that that is unexpected, given how heavy this thing is and the fact it's all made of old junk. ;) Since the rim itself is bent anyway, I chose to just start with a different wheel entirely.

--This wheel doesn't have an axle (came that way, with gummy grease; must be pretty old). Take old axle out of old wheel, and find axle is BENT. Again, not a huge surprise, but I never noticed it causing a problem.... Got axle out of an old 10-speed wheel instead, and managed to get the wheel together and trued and whatnot, and reinstalled.

--Another test ride, works kind of ok, but something wierd is happening with the assist motor. I am not sure what it is, but it sounds odd, and that could presage a real problem I don't want to have on the road somewhere. I decide to finally just change the 2-pole motor for the 4-pole I've been putting off for months.

--After much ado, get the 4-pole installed and the bike back together for another test ride. Chain comes off the motor sprocket about three trips around the block later. The torque of the motor (which is MUCH higher than the old one, at least twice as high) is pulling so hard on the chain that it actually is pulling the motor backwards in it's mounting slots despite being bolted down very tightly. To fix that, I'll have to make a different mounting plate that doesnt' have slots but rather only fixed bolt holes, which won't allow for tensioning the chain in a normal way. Not happening today.

--Since the chain will only come off if I pedal harder than the chain pulls, I decide to test it longer without any pedalling, just resting my feet on them instead, as they go round. Seems to be working fine, so I head out of the neighborhood for a longer test. First big bump I hit knocks it off anyway.

--Some 15-20 minutes of messing around with some plastic and tape and zip ties makes a sort of chain tensioner, hopefully enough to last me on the way home (it did), and head back. It's now dark, and I can see sparks in my wiring harness along the top tube. :shock: That's VERY bad. I find that one of the batteries is shifting around and a post is touching the frame, shorting across one battery. :oops: Tightened down and fixed, but now the wiring harness is damaged--some of it has melted together, and my front headlight no longer works. The midships one still does, so I'm still road-safe.

--The lefthand shifter starts to act funny, and wont' stay shifted to the highest gear unless I hold it. Dunno why yet; I ziptied it in place as I only need the lower two for hills.

Speaking of shifters, I also found when doing the 4-pole install that I had inadvertently gotten the cable for the rear shifter inside the hose clamp for the front of the seat-frame connection. It slightly crushed the housing, which explains why it has been getting harder to shift the right shifter, for the rear cluster, and less reliable when it does shift (skips several gears, etc). I'll have to replace that part of the housing. That's going to be annoying.

As for the 4-pole motor, it works quite well, and is pretty zippy off the starting line from a dead stop. I can actually feel myself being pushed back in the seat, with my feet not even on the pedals, if I startup from say, 5th gear from top (of 21).

I am certain that it takes significantly more current than the 2-pole, but both of them are beyond the meter's capability to read (12A on the analog panel meter). I have to put the HF DMM in there to see if it's less than 20A (it's max displayable amount).

This motor should be 650-750W actual power handling capability, designed for 24V. At 36V, it should be able to draw less current to do the same work, so it should be able to handle 27A steady at 24V, and 18A steady at 36V, assuming the low end of that range, 650W. Of course, 18A steady would kill my batteries in less than 15 minutes, assuming I don't want to drain them past 50% DOD. I try not to drain them even that far, where possible.

It does have a distinctive noise though: It sounds like the servo motors in robots on TV shows and movies. It's a little annoying, but I'll get used to it, especially for the better acceleration I get from it.

Because of the higher RPM of this motor's gearbox, I used lower gearing (21 teeth instead of 24) at the motor sprocket to keep approximately the same speeds. I think I must've miscalculated though, because unless something else is wrong and the rear cluster isn't shifting all the way up to the smallest ring only under load/on the road (possible, but didn't seem like it), then it simply isn't going as fast as it used to. 17.5MPH is about it.

Since I had to weld the chainring onto the motor hub, then I'll have to weld a different one on the backside of the hub and flip it over, to get the right max speed (20MPH) out of it. Probably a 22T ring. Gotta go back thru the calculations again.


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