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    M3 Snnn - Programmed vs Actual Speed

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    • Nightowlundefined
      Nightowl
      last edited by Nightowl

      I've finally got my milling motor working properly with On/Speed/Off, but the actual motor speed is different from the programmed speed.

      For example, using various S values with the M3 command, the actual speed (measured with a laser tachometer) are those shown alongside (I appreciate some of the S values are below the minimum speed of the motor and DWC would probably return an error if I tried to run the motor out of it's capabilities, but I want to see what happened!):

      S1 = 4074rpm
      S10 = 4074 rpm
      S50 = 4280rpm
      S100 = 4569rpm
      S250 = 4735rpm
      S500 = 4980rpm
      S750 = 5145rpm
      S1000 = 5306rpm
      S2500 = 6456rpm
      S5000 = 8430rpm
      S7500 = 10320rpm
      S10000 = 12250rpm
      S12500 = 14080rpm
      S15000 = 15980rpm
      S17500 = 17940rpm
      S20000 = 19820rpm
      S22500 = 21800rpm
      S25000 = 22780rpm
      

      The minimum speed of the motor (a Sorotec PV-ER) is 4000rpm at 0V and 25000rpm at 10V supplied from the PWM board, but is it critical to set the config line correctly, i.e:

      M950 R0 C"vfd" L**4000**:25000 Q1000
      

      , rather than the L0:25000 values I have at the moment, and is it likely this is causing the issue?

      Thank you.

      Few things are more dangerous than taking the advice of someone who thinks he knows what he's doing.
      I'm still on my learning curve, so take everything I say with caution!

      RatRig 1075, Duet3 MB6HC, Sorotec SFM 1000 PV-ER milling motor, Hobbyist

      jay_s_ukundefined 1 Reply Last reply Reply Quote 0
      • jay_s_ukundefined
        jay_s_uk @Nightowl
        last edited by

        @Nightowl yes, it won't be scaled correctly otherwise.
        Set the scale right and then using the screw on the pwm to analog converter to adjust the speed so it's closer to the requested speed

        Owns various duet boards and is the main wiki maintainer for the Teamgloomy LPC/STM32 port of RRF. Assume I'm running whatever the latest beta/stable build is

        Nightowlundefined 2 Replies Last reply Reply Quote 1
        • Nightowlundefined
          Nightowl @jay_s_uk
          last edited by

          @jay_s_uk

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

          Few things are more dangerous than taking the advice of someone who thinks he knows what he's doing.
          I'm still on my learning curve, so take everything I say with caution!

          RatRig 1075, Duet3 MB6HC, Sorotec SFM 1000 PV-ER milling motor, Hobbyist

          o_lampeundefined 1 Reply Last reply Reply Quote 1
          • Nightowlundefined
            Nightowl @jay_s_uk
            last edited by

            @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...

            Few things are more dangerous than taking the advice of someone who thinks he knows what he's doing.
            I'm still on my learning curve, so take everything I say with caution!

            RatRig 1075, Duet3 MB6HC, Sorotec SFM 1000 PV-ER milling motor, Hobbyist

            jay_s_ukundefined 1 Reply Last reply Reply Quote 1
            • jay_s_ukundefined
              jay_s_uk @Nightowl
              last edited by

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

              Owns various duet boards and is the main wiki maintainer for the Teamgloomy LPC/STM32 port of RRF. Assume I'm running whatever the latest beta/stable build is

              Nightowlundefined 1 Reply Last reply Reply Quote 0
              • Nightowlundefined
                Nightowl @jay_s_uk
                last edited by

                @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?

                Few things are more dangerous than taking the advice of someone who thinks he knows what he's doing.
                I'm still on my learning curve, so take everything I say with caution!

                RatRig 1075, Duet3 MB6HC, Sorotec SFM 1000 PV-ER milling motor, Hobbyist

                jay_s_ukundefined 1 Reply Last reply Reply Quote 0
                • jay_s_ukundefined
                  jay_s_uk @Nightowl
                  last edited by

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

                  Owns various duet boards and is the main wiki maintainer for the Teamgloomy LPC/STM32 port of RRF. Assume I'm running whatever the latest beta/stable build is

                  Nightowlundefined 1 Reply Last reply Reply Quote 0
                  • Nightowlundefined
                    Nightowl @jay_s_uk
                    last edited by

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

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

                    Few things are more dangerous than taking the advice of someone who thinks he knows what he's doing.
                    I'm still on my learning curve, so take everything I say with caution!

                    RatRig 1075, Duet3 MB6HC, Sorotec SFM 1000 PV-ER milling motor, Hobbyist

                    1 Reply Last reply Reply Quote 1
                    • Nightowlundefined
                      Nightowl
                      last edited by

                      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

                      Few things are more dangerous than taking the advice of someone who thinks he knows what he's doing.
                      I'm still on my learning curve, so take everything I say with caution!

                      RatRig 1075, Duet3 MB6HC, Sorotec SFM 1000 PV-ER milling motor, Hobbyist

                      o_lampeundefined 1 Reply Last reply Reply Quote 0
                      • o_lampeundefined
                        o_lampe @Nightowl
                        last edited by

                        @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

                        Nightowlundefined 1 Reply Last reply Reply Quote 0
                        • o_lampeundefined
                          o_lampe @Nightowl
                          last edited by

                          @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 ? 😄 😄

                          Nightowlundefined 1 Reply Last reply Reply Quote 0
                          • Nightowlundefined
                            Nightowl @o_lampe
                            last edited by

                            @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 ? 😄 😄

                            🙄 🙄

                            Few things are more dangerous than taking the advice of someone who thinks he knows what he's doing.
                            I'm still on my learning curve, so take everything I say with caution!

                            RatRig 1075, Duet3 MB6HC, Sorotec SFM 1000 PV-ER milling motor, Hobbyist

                            1 Reply Last reply Reply Quote 0
                            • Nightowlundefined
                              Nightowl @o_lampe
                              last edited by

                              @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.

                              Few things are more dangerous than taking the advice of someone who thinks he knows what he's doing.
                              I'm still on my learning curve, so take everything I say with caution!

                              RatRig 1075, Duet3 MB6HC, Sorotec SFM 1000 PV-ER milling motor, Hobbyist

                              o_lampeundefined 1 Reply Last reply Reply Quote 0
                              • o_lampeundefined
                                o_lampe @Nightowl
                                last edited by

                                @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.

                                Nightowlundefined 1 Reply Last reply Reply Quote 1
                                • Nightowlundefined
                                  Nightowl @o_lampe
                                  last edited by

                                  @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!

                                  Few things are more dangerous than taking the advice of someone who thinks he knows what he's doing.
                                  I'm still on my learning curve, so take everything I say with caution!

                                  RatRig 1075, Duet3 MB6HC, Sorotec SFM 1000 PV-ER milling motor, Hobbyist

                                  1 Reply Last reply Reply Quote 0
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