Accuracy of the NEMA 17 0.9°16micro-steps & THK KR2001A

Adalbert · Post by **Adalbert** » Fri Aug 02, 2019 3:56 am

Hello, everybody,

This time the step-size=0.00033mm (needed for the 3 photos a DOF for NeoSPlan 80x / 0.75 )

So, the rail has some problems to keep the stable size of the step.
The deviations are relatively big but for stacking it would be OK.
BR, ADi

ChrisR · Post by **ChrisR** » Sat Aug 03, 2019 1:41 am

It seems your error in step size reducing as the step size reduces.
Is it using smaller microsteps?

Adalbert · Post by **Adalbert** » Sat Aug 03, 2019 2:08 am

Hello Chris,
The tests with TMC5130 have been done with 265 micro-steps, the tests with TB6560 with 16 micro-steps and 8 micro-steps. TB6560 allows only 16 micro-steps.
BR, ADi

ChrisR · Post by **ChrisR** » Sat Aug 03, 2019 8:46 am

Hmm. Can you suggest why the errors (in mm, not %) reduce as the steps reduce in size?

Adalbert · Post by **Adalbert** » Sun Aug 04, 2019 12:19 am

Hello Chris,
Probably a feature of the magic TMC, maybe Mike can explain that.
The settings looks as follows:

Code: Select all

  tmcSendData&#40;0x80,0x00000000&#41;;      //GCONF 

  tmcSendData&#40;0xEC,0x000101D5&#41;;      //CHOPCONF&#58; TOFF=5, HSTRT=5, HEND=3, TBL=2, CHM=0 &#40;spreadcycle&#41; 
  tmcSendData&#40;0x90,0x00070603&#41;;      //IHOLD_IRUN&#58; IHOLD=3, IRUN=10 &#40;max.current&#41;, IHOLDDELAY=6 
  tmcSendData&#40;0x91,0x0000000A&#41;;      //TPOWERDOWN=10 

  tmcSendData&#40;0xF0,0x00000000&#41;;      // PWMCONF 
  
  tmcSendData&#40;0xA4,0x000003E8&#41;;     //A1=1000 
  tmcSendData&#40;0xA5,0x000186A0&#41;;     //V1=100000 
  tmcSendData&#40;0xA6,0x0000C350&#41;;     //AMAX=50000 
  tmcSendData&#40;0xA7,0x000186A0&#41;;     //VMAX=100000 
  tmcSendData&#40;0xAA,0x00000578&#41;;     //D1=1400 
  tmcSendData&#40;0xAB,0x0000000A&#41;;     //VSTOP=10 

  tmcSendData&#40;0xA0,0x00000000&#41;;     //RAMPMODE=0

BR, ADi

mawyatt · Post by **mawyatt** » Sun Aug 04, 2019 7:14 am

Chris, ADi,

Not sure but it might be that the errors shown are a combination of Motor cog position error, Rail screw thread error, and TMC5130 micro step error. The micro-step error would relate to the actual motor coil current waveforms and how they influence (magnetic fields) the rotor position, more possible motor induced errors (physical coil position relative to magnetic field and cog position). The Trinamic sine and cosine tables, interpolation and so on could also contribute, not too mention the actual motor waveforms and any "glitches" due to wiring, power supply, decoupling and grounding.

If the motor wiring paths & resistance are not equal, this could introduce a small error as a function of micro-step angle.

Would think that the better motors have tighter control of cog, coil and magnetic field parameters.

Best,

Adalbert · Post by **Adalbert** » Sun Aug 04, 2019 9:04 am

Hello Mike,
Thank you for the hints!

Would think that the better motors have tighter control of cog, coil and magnetic field parameters.

What kind of motor would you recommend?
I have the Nema17, 1.7A, 4200g.cm,0.9°，42BYGHM809 Wantai.

BR, ADi

mawyatt · Post by **mawyatt** » Sun Aug 04, 2019 10:45 am

Adalbert wrote:Hello Mike,
Thank you for the hints!
Would think that the better motors have tighter control of cog, coil and magnetic field parameters.
What kind of motor would you recommend?
I have the Nema17, 1.7A, 4200g.cm,0.9°，42BYGHM809 Wantai.

BR, ADi

ADi,

For example, the Lin Engineering types are very good. I suspect any of the inexpensive eBay types are not as good, like Wantai, Moon, etc. However these are usually a good choice for our less demanding macro use since a small variation is step size usually isn't an issue if you selected step sizes well below the DoF range (which you should normally do).

I have and use both the Wantai (810, 2.4A 0.9 degree) and Moon motors, also have a few of the Lin Engineering NEMA 11 motors, they are all good, but the build quality of the Lin stands out.

Best,