|
1-Axis Stepper Motor Controller Wing This is a microstepping single axis stepper motor controller based on Allegro A3979 device. Alternatively, it can also use the pin and function compatible Texas Instruments DRV8811 device. It is intended to be used with the S3E Cocoon. It can drive a bipolar stepper motor rated upto 35V and 2.5A, with a simple parallel command interface. The Wing uses a 8-bit Butterfly segment.
This board can be purchased online: Allegro A3979 based Stepper Motor Wing in Worldwide store TI DRV8811 based Stepper Motor Wing in Worldwide store Allegro A3979 based Stepper Motor Wing in India store TI DRV8811 based Stepper Motor Wing in India store
Applications
Specifications
Pinout
Direction is from the perspective of the FPGA or microcontroller.
The Prototype and BOM
Using 1-Axis Stepper Motor Controller Wing This Wing uses a 8-bit segment on a Butterfly Cocoon, like the S3E FPGA Cocoon. The board has ample copper area for heat dissipation from the tiny A3979 (or DRV8811) with thermal vias on the underside of the chip to transfer heat from the exposed thermal pad. 1. Use JP1 to select logic IO voltage between 5V or 3.3V that depends on the host device or the Cocoon. 2. Microstep selection inputs can be set from your host i.e. the S3E FPGA pins to appropriate value. 3. The logic inputs nRESET, nENABLE, nSLEEP, MS1, MS2 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 VR1 is used to set the current limit by setting the voltage that can be measured on the pad adjacent to the potentiometer. Resistor R7 ensures that the reference voltage stays within safe limits. The equation for current limit is: V(ref) = 8 x I(trip) x R(sense) R(sense) used on the board is 0.2E, therefore the reference voltage to set for desired current limit is: V(ref) = 1.6 x I(trip) A small table for reference voltage values for some values of current limit is printed on the 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 30V, and maximum recommended current limit is 2.25A, that is lower than documented limits. The 2.2K resistor R7 can be replaced with 5.1K one to ensure that the reference voltage never goes above 3.3V, to make maximum allowable current as 2.1A 2. Do not move the stepper motor shaft when power is off as it can generate high voltage transients that may exceed 35V 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 StatusThe 1-Axis Stepper Motor Controller Wing PCB's are built, tested and verified for functionality. Look for this item to be available in the store shortly.
|
|
