Step per revolution 4x of the isvexpected?

[LEO YU]

using tmc2208 stepper drive and drv8825 solderless firmware I'm expecting 400 steps per revolution in half step mode but I'm needing to 1600 steps to complete a revolution? i have tried all 4 combination of ms1 and ms2 for tmc2208 and this is the smallest.... the largest need 12800 steps so everything seem to be 4x more?

[brownrb]

Hi Leo

That is not how TMC chips work. You cant program a TMC like that. The stepper behavoir you are describing is a DRV8825 chip, not TMC.

The TMC steppers are much more difficult to get right. Step mode is not handled the same way as for the drv8825.

Big tree recommend that stepper motors are set to 1/4 step mode. Then, interpolation is enabled which the stepper will automatically use higher step modes as required.

The firmware does this. Once configured for 1/4 stepping that is all, and users should not configure the stepper for some other mode.

It is also important that the diag and ps pins are configured correctly, and the tmc chip needs to use a serial interface over which the driver can be "programmed" on the fly. Once such options are enabled, the tmc driver chip does all of that internally without user intervention.

The Solderless options presented on the project site are NOT applicable to TMC chips, because there is extra circuitry on the PCB versions that correctly interface to the chip.

I strongly recommend reverting back to DRV8825 for the Solderless version you built. There really isnt any advantage in using the TMC, other that that being less motor noise when moving. And I would also suggest that on the list of important things for a focuser, noise really isnt on that list.

Regards
Robert

[LEO YU]

Thank you!

1) I used BTT TMC2208 because I had them left over from my 3D printer projects. I can buy some 8825 i guess, using the solderless version because my solder skill is very bad and the driver board and nano shield keep things cleaner for me.
2) I updated the arduino nano to the TMC2225 firmware and it didn't make a difference.
3) The MS1 MS2 config does change the step mode but not in a way matching documentation neither in expected step count or even the expected microstep ratio, I tested each mode and counted the steps per rev

MS1 MS2 Steps per Rev   BTT Step Mode
0   0   1600    8
1   0   6400    2
0   1   12800   4
1   1   3200    16

4) I thought the TMC2208 can work in standalone mode? So am I to understand correctly if I want the TMC2208 to work correctly I need to switch the UART mode and no way to do it in stand alone mode? I mean it works, but the problem is that I'm using the focuser with a SCT which has huge backlash (6500 steps in the 0, 0 MS1 MS2 mode) which exceed the max allowed backlash value for apps like Sharpcap. If i can even HALF it from 1600 steps per rev to 800 steps that would resolve the issue for me.

[brownrb]

3) The MS1 MS2 config does change the step mode

The MS1-MS2 pins are not required for TMC, as I posted earlier, step mode is changed using a serial connection to the TMC chip. All command settings for the TMC is over the serial connection.
Only DIR, ENABLE and DIRECTION are required.

If you have 6500 steps of backlash then I would comment that your step size is extremely overkill.

Another piece of advice, For an SCT you should be looking at running the stepper motor in FULL stepmode for that very reason, I used to have an Celestron Edge HD, so I have some experience with using a motorised focuser with an SCT. Unless you are using F2 then that does not apply, but at F10 you will get better results at FULL step mode.

Regards
Robert

[LEO YU]

i 100% agree on the step size overkill that's why I'm trying to get to the 1/2 step size that's supposed to be possible via the ms1 ms2 pin. but changing the ms1 ms2 pins the resume was very much not what the spec said they should be... if i can get from 1600 steps per rec to 400 steps as a 1/2 should be, my backlash would only be 1600. Sharpcap max out at 5000 steps for backlash compensation, so even 1/4 at 800 would have still been enough at 3200 steps.

[LEO YU]

i 100% agree on the step size overkill that's why I'm trying to get to the 1/2 step size that's supposed to be possible via the ms1 ms2 pin. but changing the ms1 ms2 pins the resume was very much not what the spec said they should be... if i can get from 1600 steps per rec to 400 steps as a 1/2 should be, my backlash would only be 1600. Sharpcap max out at 5000 steps for backlash compensation, so even 1/4 at 800 would have still been enough at 3200 steps.

[brownrb]

As I said before in an earlier post
The ms1-ms2 etc lines DO NOT CHANGE STEP MODE for the TMC driver chips.
Changing those lines WILL NOT CHANGE STEP MODE

[LEO YU]

sorry i meant changing them physically via jumpers or dip switch on the expansion driver board