I'm trying to control an unknown stepper motor with the high-end timer (NHET) module of a Texas Instruments Hercules microcontroller
I got a freebee from TI almost a year ago. An unknown stepper motor, a driver board and a Hercules RM57 LaunchPad. The code to run the motor was expected to arrive too (it was an assignment for an internal) but that never materialised. In this blog series I'm trying to program the NHET module so that it sends the right signals to make the stepper step.
In the first post I'll review the hardware and check what software components of the RM57 I'll need to drive the motor. |
Hardware
I received the microcontroller, a stepper driver and a motor.
| Microcontroller | RM57 on a XL2-RM57L LaunchPadRM57 on a XL2-RM57L LaunchPad |
| Stepper Driver | DRV8711 Stepper Motor Pre-driver and CSD88537ND Dual N-Channel NexFETTM Power MOSFET on a BOOST-DRV8711 BoosterPackDRV8711 Stepper Motor Pre-driver and CSD88537ND Dual N-Channel NexFETTM Power MOSFET on a BOOST-DRV8711 BoosterPack |
| Motor | ADAFRUIT 324 Stepper Motor NEMA-17 Size - 200 Steps/Rev, 12V 350mA |
Motor
Rumours go that it's made by Seiko Denko or Emis. It's available from element14 as the Adafruit 324.
It's a 200 stepper with two coils. the wiring image below comes from the Adafruit product page. It needs an H-bridge per coil. These are part of the TI Stepper Motor BoosterPack discussed below.
Stepper Motor Driver
Hercules CPU Modules
The stepper motor controller determines what's needed.At first glance seems that I need SPI and PWM.
SPI can be done with the Hercules MibSPI module. I guess the PWM will have to come from the NHET.
Luxury Situation
The Stepper Motor BoosterPack comes with firmware for the TI MSP4320G2 controller.
I have one that I never used (long story short: there was a TI Store campaign where you could buy an MSP430 + CCS Full License for $10. 2 weeks later they released CCS7 that didn't need any license at all ... )
I can use the MSP430 to pre-test the BoosterPack and motor. And to take samples of the signals going from the controller to the driver. Luxury!
(update: I have this working. I have a testbed now to compare stepper profiles. Quite powerful.)
Some remarks from trying the application:
- For some reason, the driver reports nFAULT. The led is dim but it's detected by the software. Something to look into.
- Current to keep the motor in position: 0.607A. When that current is applied, I can't move the axle by hand. Firmly stuck.
- Running in Full Step, 512 PPS, takes 0.133A, 1/8 step 0.530A
- Going above 900 PPS stalls the motor. Anything below that seems to work for a non-loaded motor.
My next step is to try and understand the firmware for the MSP430. I don't know that one and the code is all register based. Nice learning curve ahead...
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