2-Axis Stepper Motor Controller Wing

This is a microstepping single axis stepper motor controller based on Texas Instruments DRV8821 device. It is intended to be used with the S3E Cocoon. It can drive two bipolar stepper motors rated upto 27V and 1.5A, with a simple parallel command interface. The Wing uses a 16-bit Butterfly segment.

Applications

• Position control systems
• Robotics
• Plotters and Scanners
• CNC machines

Specifications

• Integrated Dual Stepper motor driver with built-in translator with microstepping support
• ±1.5 A, 27 V output rating for each motor
  
• Full, Half, Quarter and Eighth step modes
  
• 3.0 to 5.5 V logic input levels
  
• Slow or Mixed current decay modes
  
• Internal UVLO, overcurrent and thermal shutdown circuitry
  
• Crossover-current protection
• Easy step/dir interface to host controller
• Wing interface pins can be specified down (for use with Butterfly Platform) or up (for other use) while ordering

 Following the DRV8821 documentation, the two motor drivers are referred to as AB and CD respectively.

Pinout

Direction is from the perspective of the FPGA or microcontroller. 

Testing Prototype

Using 2-Axis Stepper Motor Controller Wing

This Wing uses a 16-bit segment on a Butterfly Cocoon, like the S3E FPGA Cocoon. Following the DRV8821 documentation, the two motor drivers are referred to as AB and CD respectively.

 The board has ample copper area for heat dissipation from the tiny DRV8821 device, with thermal vias on the underside of the chip to transfer heat from the exposed thermal pad.

1. Use 'IOV Select' jumper to select logic IO voltage between 5V or 3.3V that depends on the host device or the Cocoon.

2. Microstep selection inputs ABUSM0/ABUSM1, CDUSM0/CDUSM1 can be set from your host i.e. the S3E FPGA pins to appropriate value.

3. The logic inputs nABRESET, nCDRESET, nEN_AB, nEN_CD, ABUSM0, ABUSM1, CDUSM0, CDUSM1, ABDIR, CDDIR do not have any built-in pullup/pulldown resistors. They must be externally set to their active values.

4. Phoenix connectors (terminal blocks) are used for easy integration of power sources and stepper motors.

5. Variable resistor R5 are R6 are used to set the current limit by setting the voltage that can be measured on the pad adjacent to the potentiometer. R6 sets reference voltage VREF_AB for motor AB and R5 sets reference voltage VREF_CD for motor CD.

A small table for reference voltage values for certain values of current limit is printed on the top silkscreen. Start with the lowest possible value and increase it gradually till you get adequate torque output from the motor.

Operational Limits and Precautions

1. The maximum value of motor voltage recommended is 27V, and maximum recommended current limit is 1.5A.

2. Do not move the stepper motor shaft when power is off as it can generate high voltage transients that may exceed 27V limit of the motor controller IC, leading to damage.

3. Do not set too high a current limit for a given load at required speed as this may lead to overheating of the controller IC. Current draw is directly proportional to the load and required torque. Torque is inversely proportional to the speed at given current limit. Refer to your motor data for optimal settings.

4. Always start at low speeds and gradually accelerate to desired speed, as torque output of the motor is high at lower speeds that can be used to overcome load inertia and get it into motion.

FPGA support

While this controller Wing can be operated by discrete IO signals from the FPGA or a microcontroller, a special peripheral core for the FPGA is being developed that will take care of applying timed pulses to the controller and also manage acceleration, deceleration and direction control through simple register interface. Please check the Stepper Controller Peripheral core project page.

Current Status

The 2-Axis Stepper Motor Controller Wing PCB's are currently being built and tested. Look for this item to be available in the store in the next couple of weeks.

• Board Design - Complete
• Board Manufactured - Complete
• Board Assembled - Complete
• Preliminary Testing - Complete
• Board completely Verified - In process
• Board available in Store - Pending