It works!
I'm frankly just amazed at how well it works, too!
The set-up
- A Towerpro 5330-10t motor, fitted with three Hall sensors spaced at 120 degrees around the stator, in slightly machined-out stator slots. All three sensors are fitted with the "spot" face outwards (see photo in previous post that shows how they are fitted). I haven't got around to testing the external sensor idea yet, and may not now bother with it.
- A baby 6 FET 48V, 15A Infineon controller, with stock current limit and no firmware changes.
- A 48V bench power supply, current limited to 2A.
- a 5k pot wired as a temporary throttle control.
Here's a picture of the test set-up:
The results
- The motor starts very, very smoothly indeed, there's absolutely none of the jerkiness that the big 120A Swang Hobby ESC gives at all.
- The slow speed torque is simply incredible. I cannot stall this motor by grabbing the shaft, even when it's only running at a few rpm. "Idle" speed seems to be right down around 50rpm or so, with an idle current of just 91mA off load at this speed! This is a direct contrast to the performance with the sensorless controller, where low speed torque was non-existent by comparison.
- At full speed, no load, the motor draws much less current than it did with the sensorless controller, even allowing for the higher operating voltage, implying a bit better efficiency perhaps. The RC ESC drew over 200mA even with the motor stationary at zero throttle, the Infineon is drawing just 59mA in this condition.
- The only downside is that at very low speeds with a lot of torque loading on the motor the controller FETs started to get very slightly warm (maybe 30deg C), even though the supply current was pegged at just 2A. I was running it without the case, though, plus the FETs in this controller are still the high Rdson ones it came with. Fitting the IRFB3077s should reduce the controller losses by a factor of four, so leading to less heating, although I don't think it's really a significant issue.
I managed to get the Hall sensor and phase wire orientation right first go, by the simple expedient of driving the motor with the RC ESC and putting the 'scope on each Hall sensor in turn, comparing it's switching point with the zero crossing of the phase voltage.
I very strongly recommend this way forward for driving these big RC motors. The big, 18 FET Infineon controller should be OK for 80 to 100A at maybe 72V, enough power for the biggest budget RC motors. Even a Kelly controller might well work well with this mod, opening up even more powerful motor possibilities.
The smoothness of this controller/motor has to be seen - it really is super smooth compared to the sensorless controller, plus the motor runs much more quietly at all speeds. The massively increased low down torque will also make gearing easier, as there shouldn't be any need to consider using two speed systems I think - just gear for max speed and let the increased motor torque take care of the low speed end.
I'm dead chuffed with the outcome of this experiment, it's turned out better than I would have hoped.
Jeremy