BritishIdeas
Interesting Tech Projects
Stepper Motor Drivers and Interface
Oct 8th
We have to connect the stepper motors (three, one each for X, Y and Z axis) to a PC. This is achieved with an interface board and drivers. The interface board typically connects to the PC’s printer port and then connects to the drivers. We need one driver for each stepper motor.
When looking at what is available there are a lot of choices. Some come in kits, some are open source and some are just pieces of designs. I decided not to use the design used by Tom McWire for a couple of reasons:
- Using a microcontroller on the board reduces some of the real time requirements on the PC. The microcontroller can perform some local processing instead of having to rely on the PC to provide all the signals
- Supporting microstepping allows for finer control over the motor. Essentially microstepping further divides the steps provided by the motor. This can give a higher precision and smoother operation
In addition I have the following requirements for the hardware:
- Able to be configured to support specific PC applications
- Simple design
- Able to drive NEMA-23 stepper motors
- Uses a common microcontroller
- Preferably open source
I found the following website full of designs: PMinMO Electronics, including a Parallel Port Reference. Of these designs only a few support microstepping. Of those I am currently considering using the PICStep. Further research is required however to make sure it will be possible to interface to the PC applications I am interested in using.
Low Cost CNC Milling Machine
Oct 4th
The primary purpose of this blog is to document specific technical projects that I will have a go at. First up is an attempt at building a low cost but precise CNC milling machine. I will follow the design by Tom McWire shown here: Easy to Build Desk Top 3 Axis CNC Milling Machine.
So now you are wondering, why bother if how to build this machine has been described on the internet already? Because my aim is reproduceability and accuracy. The problem right now is that if two seperate people decide to each build a machine from the instructions, they will end up with slightly different machines that perform differently. For example the dimensions of the machine and which stepper motors used are missing. I want a set of instructions that people can follow to yield predictable results.
Also missing is a description of the kind of accuracy that can be expected. At this point I am not sure if this machine can generate an accuracy good enough for my needs. Hopefully it will. If I can figure out what design decisions to make to achieve the accuracy I need, and document them, then other people will know up front exactly what they need to do to also get the same accuracy. My aim is to be able to engrave commemorative coins. These coins have a small area where a name can be placed, and this will require precision.
I hope to also make some minor improvements here and there, and it might involve a few iterations before the machine works well enough. One of Tom McWire’s aims was to build it in less than $200. I also have the same aim, but if a situation arises where I can spend a few dollars more to increase precision then I will do it. For example I won’t be getting old motors from printers because they are all different and someone else cannot then come along and follow my instructions to get the same machine. Instead the specifications of the motors I use must be known.
(picture from Easy to Build Desk Top 3 Axis CNC Milling Machine)
