M3 Snnn - Programmed vs Actual Speed

Nightowl

Thank you. I'll do that tomorrow, as it's too dark to go out now

Nightowl

@jay_s_uk
That's made a significant difference, although I will need to tweak the converter somewhat.

These are the latest results:

M3 S...
4000 = 4050rpm
6000 = 6266rpm
8000 = 8150rpm
10000 = 9955rpm
12000 = 11665rpm
14000 = 13473rpm
16000 = 15304rpm
18000 = 17065rpm
20000 = 18867rpm
22000 = 20726rpm
24000 = 22425rpm
25000 = 22608rpm

My normal range of speeds would be between 10000 and 18000 for my CNC, so they're not too out of whack, I'd like to get them as accurate as I can...

jay_s_uk

@Nightowl do you find the RPM is wondering about a bit? because it does on mine. Or is the value staying stable?

Nightowl

@jay_s_uk
It does seem quite stable. The only exception was with the last list of speeds, where one of the speeds 'hunted' a bit, like a vehicle engine with a touch of fuel starvation, if you know what I mean?

jay_s_uk

@Nightowl yea, that's what mine sounds like. Maybe I need to revisit my setup

Nightowl

@jay_s_uk
Whilst checking the speeds, I also checked the noise. At...

Ambient = 45dBa
S4000 = 65dBa
S10000 = 75dBa
S18000 = 83dBa
S25000 = 84dBa

Nightowl

So, I've done a bit of tuning with mixed results.

M3 Input - Untweaked	- Tweaked
S4000	– 4050		– 4060
S6000	– 6266	 	– 6550
S8000	– 8150	 	– 8485
S10000	– 9955	 	– 10400
S12000	– 11665		– 12270
S14000	– 13473		– 14030
S16000 	– 15304		– 15870
S18000 	– 17065		– 17680
S20000 	– 18867		– 19390
S22000 	– 20726		– 21190
S24000	– 22425		– 22880
S25000	– 22608		– 23050

There doesn't seem to be a regular variation, so I was wondering if anyone else has managed to work this out and achieve accurate speeds.

Thanks

o_lampe

@Nightowl
Did you measure RPM under load or without?
I think, the RPM control loop works best under load? (except with 3-phase PM brushless motor)
All other motors, (brushed DC or asynchron) are less accurate

o_lampe

@Nightowl said in M3 Snnn - Programmed vs Actual Speed:

I'll do that tomorrow, as it's too dark to go out now

How dare you to name yourself nightowl ?

Nightowl

@o_lampe said in M3 Snnn - Programmed vs Actual Speed:

@Nightowl said in M3 Snnn - Programmed vs Actual Speed:

I'll do that tomorrow, as it's too dark to go out now

How dare you to name yourself nightowl ?

Nightowl

@o_lampe said in M3 Snnn - Programmed vs Actual Speed:

@Nightowl
Did you measure RPM under load or without?
I think, the RPM control loop works best under load? (except with 3-phase PM brushless motor)
All other motors, (brushed DC or asynchron) are less accurate

No, I didn't test it under load to be honest. It may have been optimistic on my part, but the blurb indicated the speed is maintained under load, so I'm wondering if I should test the voltage output from the PWM converter (as supplied to the milling motor) to see if the issue is there.

I have more confidence in the German-built milling motor, than I do in the converter and/or the digital tacho I'm using to test the speed.

o_lampe

@Nightowl said in M3 Snnn - Programmed vs Actual Speed:

the digital tacho I'm using to test the speed.

I suspected that too, but those would usually skip pulses. But in you table it reads more pulses at low RPM. Probably false triggering...
I had good results with hall sensors. A simple bicycle speedometer (with programmable wheel circumfence) worked well on my wind turbine.

Nightowl

@o_lampe
Perhaps it's time to start another hobby....

The idea of using an Arduino with a hall sensor sounds like fun, and I've seen an Arduino kit on Amazon which seems to fit the bill (except for the hall sensor, which is cheap enough), but I wonder if this would be more accurate than a laser measuring the reflection from reflective tape stuck to the spindle's collet nut - which is the method I currently use?

Of course, I'd need to learn how to program an Arduino!