rhitee05 wrote:You can easily do this by supplying a square wave input to the motor hooked in series with a moderately-sized resistor, say 1k or something. Measure the voltage across either the motor or resistor and you can calculate the time constant from the waveform, which will be L/R (R = the external resistor). This is a pretty easy trick that I teach my students in intro EE lab. You might need to choose a different value for R, depending on how good the resolution on your scope is and roughly what you expect L to be. If L is 100 uH, for R=1k the time constant would be 100 ns. The period of the square wave should be quite a bit longer, so 1 MHz or less probably.
Thanks! That actually sounds familiar, so it might be how we did it in lab way back then.
If I had the signal generator out I'd try it right now, but it'll have to wait until I have time to find it. The scope is a 20MHz bandwidth, but I don't remember what the best div on screen is (for either the giant Tek 531 or the mini Hitachi).
Earlier, I finally decided to just get the halls in there to test this thing, because I wanna see it spin on i'ts own.
So I unbolted the stator from the base plate,
and mounted the halls from underneath it (so the wiring will all be protected from the rotor, and so that the halls will be closer to the air circulation from the baseplate/rotor gap--right next to it, in fact).
To keep them clear of the rotor, but without doing anything to the stator lams, I notched the filler sticks between the teeth instead, and superglued the halls to those (I didn't want to use epoxy yet, as I didn't even know if they would work there, plus I have no epoxy that would hold up better than superglue anyway).
Naturally, it can't all go right. I managed to break a leg off the yellow hall while holding it and it's wires down while the glue set.
I did manage to fix it, after over an hour's dinking around with magnifying glasses, several flashlights and other lights to help me see, scraping plastic off the case away from the remainder of the leg (not even a quarter of a millimeter!), and several tries with the tiniest soldering tip I have. Eventually I got the leg glued down first and then soldered with a glob of solder to the hall. It's the output pin, so I'll know pretty well when it comes off again later.
Probalby when I have forgotten it was even broken.
All the duct tape came off after I got the wires all secured down (dots of superglue here and there to the stator endplates; they won't stay glued but will hold long enough for assembly) and halls glued in place. That was at least an hour and a half to hold wires while glue set (tape ripped them loose when removed, so had to hold by hand utnil set).
I had to take it apart twice because of pinched wires, as I didn't move them all out of the way of the baseplate's riser edge, apparently, and ended up with continuity from power and ground to the baseplate.
There went another hour or so.
This is the EVAssemble "36V" 12FET I used to test it with, and it works well enough, though the red LED on the PCB flashes all the time it's powered on (can see it thru the end of the case for the wires, which I don't have screwed down). I bolted it tot he motor with the bottom motor baseplate screw, thru the end plate of the controller. Can't quite do what I planned and bolt it diagonally across the baseplate, because the phase wires are a cm or so too short.
The phases are bullet-style, female, so I just removed the thick plastic housings that wouldnt' fit in teh D-style motor connector, wrapped the bullets in electrical tape to prevent accidental contact, and plugged the bullets onto the large round phase connector pins in the D-connector.
The motor hall wires I just tinned the ends of and stuck them into the female contacts of teh controller's white hall connector.
The whole test setup, using the Sorenson DCS 55-55 at 40V, 10A current limit, to simulate my 36V NiMH pack that isnt' currently charged up enough to use for the test.
Scope is setup with a Phase (blue) on top at 10x / 2V/cm, and a hall (blue) on the bottom at 1x 2V/cm. I forget what the time setting was at. WattsUp from AussieJester used to monitor power usage.
It took one full set of hall combinations (6) and then one phase swap and then 3 more hall combinations to find a smooth low-current no-load spin condition, at about 1.6A no-load current full throttle at 40V.
Ended up with Y-G-B on the phases on the motor connector, and G-B-Y on the halls. (in case I forget later)
Video of operation at 40V:
Later I took it up to nearly 56V, which is as high as the Sorenson will go, and also as high as I think I should go on the 12FET.
But it does work, on a cheapy type of ebike controller, at least at no load. I'll have to bolt the baseplate to something and try loading down the motor, probably via friction to CrazyBike2's front motor wheel in regen mode to a depleted battery.
If it still works ok, maybe I can mount it on CrazyBIke2 in the center frame, bolt a chainring to the face of the rotor, and connect it up to the chainline, and see what breaks first.