Motorspeed on Full, Half and 1/4 Step on myFP2_DRV8825HW203_301

Version 2 of the myFocuser Project

Brought to you by: brownrb

Motorspeed on Full, Half and 1/4 Step on myFP2_DRV8825HW203_301

Forum: General Discussion

Creator: Andreas Exeler

Created: 2020-11-29

Updated: 2020-12-03

Andreas Exeler - 2020-11-29

Hi Robert,
i build myFocuserPro2 new (because the to small Stepsize on my old Hardware).
Now i use a Stepper with 7.5° per Step (42 Steps per round) and the Motor gets Hot (no CoilPower on) and i found out that the Pin8 (drv8825 enable) was shortcut to GND.
I cut the layer in the PCB, Coilpower is now OK. (enable and disable works now).

But i think there is a other fail in my Focuser.
The Motorspeed change from slow, Mid and Fast works in Full and in 1/4 Step Mode, but in Half Step Mode the Speed is much slower then in Full or 1/4 Step Mode.
Is this possible?
I Use the PCB 4.2 from DRV8825-HW203-RE Manual.

Thanks for Help and your great Job!

Greets
Andreas

Last edit: Andreas Exeler 2020-11-29

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Andreas Exeler - 2020-11-29

Hi Robert,
the same poor speed on 1/8 Stepmode, but on 1/16 Stepmode the Speed (RPM of the Stepper) is much higher!?
Greets
Andreas

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brownrb - 2020-11-30

Hi Andreas
I had made an attempt in the firmware to get the speed somewhat the same.

The problem is that with 1/4, 1/8/ 1/16,it becomes near impossible to control the rotational speeds or make them any where near the same as full and 1/2 step. One would end up just trying to pulse the motor too fast and the result would be lost steps. At 1/8 step the motor is moving 1/8th the distance of a full step - to get the same speed you would have to pulse it 8x faster - and there is a definate limit to how fast you can a stepper and we are near those limits now.

The loss in torque when you get below 1/4 step is huge which is why the advice is always try to gear things to full stepping.

Full = 100% torque
Half = 70% of full torque
1/4 = 70% of half torque
1/6 = 70% of 1/4 torque and so on.

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Andreas Exeler - 2020-11-30

Hi Robert,
sure, but on my new Focuser is the "true" RPM on the Stepper on Half and 1/8 Step-Mode about 10 times slower then on Full, 1/4 and 1/16 Step-Mode.
I will check the M0,M1,M2 an try to messure the pulssize and timig.
Greets
Andreas

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Andreas Exeler - 2020-12-03

Hi Robert,
i am sorry, it was my fault!
The M0, M1, M2 on the DRV8825 came on wrong signals, (eg. on Half-Step the M2 was High).
After two Clean Set (Arduino and PC) the Signals are OK.
Now i can Test the new Stepper.
Sorry for my fault.
Greets
Andreas

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brownrb - 2020-12-03

Hi Andreas
No problem, happy to hear issue is now resolved

Regards
Robert

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