amberwolf wrote:But I don't have anything that will measure inductance at all, so what I was pondering was using a signal generator (which I have around here somewhere, if it works) to pass a specific amplitude and frequency thru a pair of windings, and see if it is delayed by an amount I can measure on my scope, and maybe calculate it from there? I have to look up the procedure for doing this, because I am probably forgetting an important step or component, like having a known capacitance in there, too. I remember doing it in the lab at school, as one of the lessons, but that was 1988 and I don't think I have done it since then.
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.
amberwolf wrote:I wish I had remembered this thread existed before embarking on my latest motor project...but now that I've re-found it...
I need to re-read this entire thread again (just finished reading it the first time now), but while I do that, and try to actually absorb some of the information that seems to be bouncing off right now, perhaps some input on my "project":
I've got a huge (20lbs+) brushless powerchair motor that's about the same size stator as something like the X5 series, I think, but it's wound to directly drive a small powerchair wheel (14", I think) at either 4 or 8MPH at 24V (really 28V, two SLA in series).
Built in it has SIN/COS analog sensor output...which is useless (without translation hardware) for ebike controllers (which is what I have avaialble to drive it). I added digital hall sensors at 120 degree physical intervals, gluing them temporarily with just superglue to hand-carved recesses in the material covering the windings between stator teeth.
It's a 45-tooth, 40-magnet, Wye-terminated motor. Presumably it is 15 poles? No idea on number of turns/etc, or inductance (yet, I have a plan to test that later once I find my signal generator).
Presently, the no-load full-throttle current at 40V is about 1.6A, and at 56V is about 1.7A.
There are pics and videos and further data in it's thread over here:
if needed, or at request I can repost them over here in this thread.
What I would like to find out is what the optimum placement of sensors might be (for timing and high-load situations), if not where I already have them.
At present, there is definite clicking (of changing fields, not mechanical) at each part of a rotation equal to magnet passing stator tooth (or more than one tooth). That might simply be how it works with an ebike controller using trapezoidal commutation, and it might be smoother with a sine controller (but I don't have one). But if it can be made better by simple hall repositioning, I'm up for trying that, if anyone has a fairly certain idea of what might work better. I can't reposition them much, or I'll break the leads off (already did this to one and barely fixed it), and I have no spares except what is in other motors.
What I had planned was to install them on a ring on the outside of the mtor, but there isn't enough flux leakage for them to pick up, so they had to go inside on the stator.
There *is* another magnetic encoder source, which is the ring used for the analog SIN/COS output. I could probably mount them inside there where they can detect the domains on the ring, but I dont' yet know how many there are; if it's less than the number of magnets on the rotor, I'm not sure how things would work with an ebike controller.
Alan B wrote:Stainless work hardens easily, need the right drill bit, lubricant, and speed. Probably work hardened and dulled the drill bit.
Alan B wrote: Probably work hardened and dulled the drill bit.
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