So my PS can be over volted to 30V. At 30V I can easily hit 35k RPM. Only issue is my cooling fan for my electronics enclosure is not happy at that voltage. Might switch it to run off the Carbide Motion Board.
On the motor windings (stator), since the Makita’s housing is insulated from it. But the rotor will also heat up from eddy currents. RC community blogs suggest that it needs to be kept below 60 degrees C to prevent de-magnetization and/or glue failure - but who really knows?
So I have the code running well enough now that I do not need to set the RPM in ODrivetool. It does it automatically from the PWM output. Soooo much nicer than having to fuck with a router control knob or typing in commands.
Need to work on the fault handling and the temperature monitoring of the motor coils.
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That’s great, seems to be properly coming together.
You might want to consider coding in;
- a “probing mode” which locks spindle RPM to about 1,200 RPM for edge finders (definite risk of injury if one of those goes to 30,000)
- a “bit changing mode” which locks out the spindle completely, this could be a Normally Closed ‘run enable’ button on an input pin
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Two very good ideas, but first I want to get the Fault Pin code working.
I received another email from Harvey Tool today about their high speed endmill/drills that reminded me of your earlier post about drill/endmills.
Does O-Drive use the hall sensors?
It works with Hall Sensors yes. It is not working with the Makita above 10k RPM for some reason. Hopefully will be hooking the motor up to an oscilloscope today to try to figure out why.
Hooked it up to the scope earlier and saw a very nice sine wave. So either the motor has too low of an inductance or the hall sensors are noisy.
Vince’s VESC says it has zero inductance (and no hall sensors).
I measured 27 micro Henrys across the winding leads for my similar 18V BLDC Milwaukee router with this meter: I also measured 9 micro Henrys for this “Out-runner”.
But I measured 340 milli Ohms across the Milwaukee windings, which is a lot more than the VESC’s 9.5 milli Ohms.
Maybe the voltage supplied to the Hall sensors is marginal?
I was surfing youtube and saw the new Bantam cnc is using a hobby grade outrunner BLDC motor to drive their spindle.
When I suggested a chip guard to prevent conductive chips from being sucked into the motor windings I got the best response that could only come from a sales rep that has no idea about what I was referring to
Bantam Tools
Hi there! We future-proofed the machine to accept an air blast system to help with chip evacuation. Be on the lookout for that accessory later this fall!
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It looks like an in-runner to me - why do you think it’s “hobby grade” motor? They appear to have done their homework - their design is quite impressive. Too bad they apparently didn’t provide real time operator feedback of cutting power, force, and endmill deflection. Maybe that’ll be a future accessory too.
The entire housing spins in the video and the wires come into the front of the motor. Outrunners are not sealed motors. Inrunners are sealed and the housing stays stationary and just the rotor spins inside.
The use of an outrunner is for more poles which leads to more torque and it’s not a bad thing because it’s spinning a proper spindle cartridge so the bearings on the motor are not taking a beating. The only problem I have with the design is the exposed windings of the outrunner can let conductive chips into the motor possibly shorting it out. A simple screen of some sort around the motor would prevent this.
This is NOT the motor they use just an example of how the windings are exposed on outrunner motors. Now imagine aluminum chips in there.
That’s just one reason (of many IMO) not to use out-runner motors in this type of application. Airflow (rather than conduction) is necessary to cool the stator windings.
@CthulhuLabs’s in-runner recommendation makes a lot more sense to me.
The ODrive is measuring the phase inductance of this motor as 8.36 uH. Which is on the low end of what ODrives can handle apparently. I have three 22uH 28A inductors that someone suggested I wire into the phases to see if it helps.
It will be interesting to see how far that pushes the drive voltage up for the same RPM.
I measured 27 micro Henrys at 1100 Hz with my meter, so that seems consistent. Does the ODrive give you winding resistances?
What’s the dc resistance of your inductors?
I doubt the new Bantam will have issues with chips inside the motor. This is the PCB mill with its teeny bldc outrunner, very nicely protected. Usually something spinning that fast creates its own airflow to a certain extent which should help keep chips away. I never used a chip fan during all my hours of aluminum machining.
It’s also been connected to the VESC.