OnStep Controller Hardware
There are three paths you can take to build your controller:
1. Use general purpose commodity hardware to build your own wiring everything together; we generally don't recommend taking this path.
2. Use 3D Printer and Engraver commodity hardware.
- We recommend using either the FYSETC S6 or WeMos D1 R32/CNCV3.
- The FYSETC S6 is more expensive, more flexible, and of good quality (typically.)
- The WeMos D1 R32/CNC3 makes a nice low cost basic controller.
3. Use a purpose designed controller like one of the Mini series or the Max series.
- We recommend:
- The MiniPCB Version 1 for a basic 2-axis controller if integrating into a mount.
- The MiniPCB Version 2 for a basic 2-axis controller stand-alone in its case.
- The MaxSTM Version 3.6 for a 4-axis controller with encoder, home switch support, and flexible auxiliary control options.
- The MaxESP Version 3 for a 4-axis controller with encoder and home switch support, but fewer auxiliary control options.
Basically any motor driver with step/dir inputs will work but the current chopping bi-polar stepper drivers are the ones usually used. Keep in mind the stepper motor that you plan to use will have a current rating and that should be within the stepper driver's capabilities. Below I cover the StepStick type drivers that we often use for this application. For large mounts that require NEMA34 and up stepper motors there are step/dir interface equipped stand-alone stepper drivers that can run these powerful stepper motors. Also step/dir interface equipped servo drives should work too.
For most users the StepStick style drivers as detailed in this in this summary are suitable to the task and the following are our recommendations:
- In most cases the SilentStepStick TMC2130 and TMC5160 (read about the TMC2130 and TMC5160 before buying!) will offer the best overall performance and feature set.
- The LV8729 is the budget champ but it isn't a good match for the Mega2560/RAMPS/Mks Gen-L builds (unless you are up for a little soldering and add jumper leads to plug in and allow OnStep to switch micro-step modes on the fly.)
- The S109 is good higher current capable option that's also budget friendly.
- The long available A4988 and DRV8825 seem to have more difficulties with smooth micro-step motion on a variety of hybrid stepper motors so their use should be limited to "tin-can" permanent magnet stepper motors, if they are used at all. Their only positive attribute relative to other options is low cost.
There two frequently encountered types of stepper motors. Permanent magnet "Tin-can" and Hybrid. Additionally, these will usually be classified as bi-polar (4-wire) or uni-polar (usually 6 or 8 wire.) Most of these stepper motors will work with a bi-polar driver by simply omitting a lead or combining the leads in certain ways, a little googling will find examples of how its done.
- Tip: There are other 3-phase and 5-phase stepper motors that will not work with a bi-polar stepper driver.
The Tin-can steppers (of a given size) are less powerful than a Hybrid stepper. They tend to come in 24 or 48 step per rotation models and often have a gear-head installed. The Hybid steppers usually come in 200 or 400 step per rotation models and more often don't have a gear-head installed.
Use my Configuration Calculator spreadsheet to see what range of gear reduction is workable, keep in mind that sometimes the best design is the one that's easiest to implement, gets the job done, and is reliable. It helps to test the stepper motors (and OnStep) "on the bench" before putting it all together. That way you might notice/correct performance as well as some acoustic issues (noise) before spending more time and effort on a unworkable design.
For an illustration of how stepper motors work, you can view this short video.
Often there have been others who have implemented and verified drive designs for common mounts, see the Showcase for ideas. If you're designing your own unique mount/drive and have carefully considered requirements be sure to read over the Wiki sections on Drive Design and Stepper Motor Accuracy.