Stepper Driver Choice
Stepper Driver Choice
Before purchasing any motors for your printer you should always check what drivers are available for the control board you are going to use. The next step is to take a look at the available drivers data sheets. The most important items to help with the final motor choice are the driver Continuous current and if the driver allows you to adjust the stepper current (some boards have this built in).
We have chosen to use the Rumba (V1.1) control board and the drivers that are compatible with it are the A4988 and the DRV8825
|PCB Colour||Green Or Red||Purple|
|Maximum Micro steps||up to 16||up to 32|
|Adjustable Stepper Current||Yes Trim Pot||Yes Trim Pot|
|Rs Values||0.05 or 0.1 or 0.2 Ohm||0.1 Ohm|
|Vref Formula||Vref = Current Limit x 8 x Rs||Vref = Current Limit / 2|
|Driver Continuous current without heat sinks & cooling||1 Amp||1.5 Amp|
|Driver Continuous current with forced cooling & heat sinks||1.7Amp||2.2 Amp|
|Thermal Overload Protection||Yes||Yes|
To get the full torque from your motor you should always choose a driver with a continuous current greater than the motor rated current per phase. Then reduce the current limit on the driver to match the rated current of the motor. It is very important to carryout this procedure before you connect your motors as we find new driver current levels are always set high. This will cause damage to your motor even if it is not moving because generally stepper motors always have current to hold position.
Looking at the motors we are planning to use
- For X, Y and Z axis the Nema 17 (17HS4401). These motors have a Rated Current/phase of 1.7 Amps.
- For the Extruder the Nema 17 (17HD34008-22B) has a Rated Current/phase of 1.5 Amps
The rated current/phase on our Nema 17 axis motors are 1.7 Amps so this would be pushing the A4988 driver to the top of it’s limit even with the forced cooling and heat sinks. We could choose a motor with a smaller current/phase rating but then we would be losing torque and we do not want that. Therefore the DRV8825 would be the better choice as it will be operating in its lower limits and it gives us space for future motor upgrades if the alloy heated bed requires a motor with more torque.
The A4988 driver maybe able to cope with the extruder motor as the 1.5 Amps is within the drivers top limit. We would have to fit heat sinks and we have already planned to have cooling fans on the electronics case so the A4988 is an option. What else can we look for?
Well the DRV8825 is capable of 32 micro stepping that means the filament extrusion can be controlled better especially on small detailed prints with finer nozzles. For this reason we will be using the DRV8825.
Another advantage of a driver with a large continuous current is that it gives you the option to run more than one motor on the driver. To do this you must consider both motor rated currents if you decide for some reason to wire the motors in parallel. For example if we wanted to do multi printing (side by side heads) we could run two Nema 17 motors with rated currents of 0.8 Amps (1.6A total) on the same driver. On an Core-XY design you would do this to both the X and Y axis drivers plus the extruder driver. You can now print the same item twice, side by side with only four drivers in the time it takes to print one. Ummm one for later….maybe?
Some useful links with reference to this blog
Wiring Stepper Motors In Series