DC Servo Motor Controls

The purpose of this section is to discuss motor controls for the DIY Drones CNC project.

There are really only two options - purchase ready-to-go controls or DIY/kit controls.

A major player in online motor control information is CNC Zone. They have had open source and commercials control discussions for years. It is a priceless resource.

The DIY Drones CNC project is a budget bound project. As such the emphasis will be on price.

If when a mechanical assembly (the steel/metal parts) is made, the drive system for the motors can be the owner's choice if price is not an object.

All electronics are subject to obsolescence. What is hot, popular, and fast today may be cold, common, and slow tomorrow or next week.

My gainful employment and hobby has been in the electronics world for over 35 years. It continues to change and amazes me constantly at the power we now have at our finger tips.

With only one CNC project under my belt, I am no expert. On the other hand, the 2nd CNC project is always in the back of my mind.

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  • OTS (off the shelf) motor control #1

    Jeffery Kerr PIC-Servo SC This brushed DC motor controller is available through Jameco. The max current of the board is 3A @ 48VDC continuous and  6A peak. It uses RS-485 to communitcate with the board. A RS-232 adapter is available. It uses a power IC, similar to the MakerBot Servo controller and not discrete FETs. Single unit price is $160 with price breaks at 5+ and 25+. The best price is $145 each with 25+. The RS-485 interface would require some research on the control software because the board does not use the simple parallel port approach to motion commands (like TurboCNC and others that use the parallel port for X, Y, Z drive).

    For a single purchase buyer, this control scheme would set you back $480 for 3 axis, NO control PC, software, cables, power supplies, and everything else needed to get a machine running.

  • DIY motor controls #3

    MakerBot DC Servo Controller This unit, at $65, is a bargain but somewhat lightweight for our purposes. The max current is specified to be 2.8A @ 36V. This motor current is through the H bridge chip, the A3949 from Allegro. The plus side of the product is that is comes ready to use with wiring and connectors supplied. The negative side is that it was designed integrate to MakerBot's encoder products. Those are a magnetic linear encoder - kinda neat at $50 and their magnetic rotary encoder at $50.

    Using their products, a functioning servo is $115 AND we are still limited to 2.8A of motor current.

    At this time, we do not have specification for forces needed to perform the desired machining. Commercial systems have higher current ratings (and bigger motors) because the motors may be called on to make heavy cuts or cuts on hard materials.

    I think these electronics would be fine on a wood working machine of some type. Until we get more information about the forces needed in our project, I have reservations regarding metal work using these controllers.

  • From what I can determine, the ELM Chan and UHU boards developed somewhat in parallel though the ELM Chan seems to have been the genesis idea - I could be wrong. There is very little difference between the two and the attached zip file is a blended version is seems. Eagle is needed to view the schematic.


  • DIY motor control #2

    UHU Servo This not-so-open source project has been around a while. CNC Zone has a very active section on this design. The controller chip is *only* available from the originator. Do not expect a neat clean store interface if you want to obtain the controller chip. The good news is that a commercial blank board is available from EAS. At the time of this post, the board was $10 + shipping. There is a Digi Key part number BOM at the top of this project secition. I have 3 of the boards and plan to build them for testing/use. More good news is another source for a drop-in replacement for the controller chip is available, Henric's page for his controller.

    Homepage Huber
  • DIY motor controls #1 (not the first choice, just the first discussed)

    Elm Chan  This open sourced project has been around a while with the last updates made in September 2009. No commercial blank board is available. It has a chip count of 4, 6 if your count two 3-pin voltage regulators. It uses a classic H bridge motor drive. The control chip is a ATTiny2313 from AVR. At least two discussion threads on CNC Zone exist for this project. There are claims of success with TurboCNC control software somewhere in those discussions.


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