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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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.
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.
The really good news is I don't think there is very much difference between #1 and #2 in general.
It seems the UHU controller program was the best at the time and probably now- Henric's controller handles faster encoders. It has gone through 3 version updates (current version). The circuits are nearly identical. There are code listings of builders on the CNC Zone sections and I suspect that we have some good code talent around these parts who can adapt/improve the situation.
The EAS version of the circuit has several features not found in the originals. He has quoted me a 50+ quantity price of $8/board. That is *bare* board to be clear.
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.
Yeah, that's great. What is the web site for the ELM? Can you post a link so that I can reference it, when I send out the email to my board guy?
It is in the post up top.. but here it is again..http://elm-chan.org/works/smc/report_e.html
Note the original date is 2001. Me thinks this project predated UHU. Uli just ended up with code for his controller.
UHU-HP (high power) is another candidate. I have not studied that variation yet.
I have about 3 more DIY motor control posts before starting sections called "OTS (off the shelf) motor control".
Again, the EAS board is essentially the same as all the later variations (except high power). EAS has added some features that can be used, or not, depending on the application and interface to the PC.
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.
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.
If we have a good open source design, I think it's a good idea, if 3DR makes the boards.
I too agree that having 3DR involved is a good idea.
What we don't know is their level of involvement.
Do they want to support/sell hardware from an open source design from 'Us' i.e. be a job shop/board house?
Do they want to design the entire thing? (not likely as it is out of their normal realm).
I keep adding/suggesting options for motor controls because regardless of 3DR involvement, not everyone is going to do the same thing. My additions are somewhat of a 'review' of the controls based on my experience and the specification sheets.
3DR has a lot on their plate just keeping up with APM and related projects and learning to develop a customer service/support group. I suspect if we had the perfect motor control design yesterday, there would be a significant delay before we saw product.
Monroe, I don't think the motor decision is not a show stopper for the rest of the project.
The frame should be designed for standard sized motors, and to accept the encoders, so as to be able to accept both the servos and the stepper, right? Also, as far a software is concerned, I think we should have enough volunteers, in this group to be able to handle it. Once we get all the hardware figured out, we can start on the software aspect.
I totally agree with you that servos are the best. But having the flexibility of both using steppers and servos will make the machine more accessible to everyone. Would the stepper and servo solutions would be compatible with each other, and people could start with the steppers, and have the potential to upgrade to servos, in case they later plan to do production work.