Yeti – Electrical Design Part 1

I always knew that the electrical side of this project would be difficult but I hadn’t realized quite how difficult it would be. With the mechanical aspects of the build at least you can look at either the part or a 3D model and have a good understanding of whether it will fit together / work / etc. With the wiring you have a bunch of parts, each of which has tens of connectors that all need to be joined up correctly. Then there’s all the other little bits that need to add to the circuit for safety or to control this or that.

I started by reading a lot of threads on a lot of forums about electronics and came away with little more understanding than I started with. For some reason people don’t generally seem to discuss the electonics that control their machines in a way that is accessible to beginners. Everyone (apart from me) seems to start at the point where they know basically how to wire the thing together and just need some detailed advice on exactly which thingy-m-bob will invert the charge coupled whatsit.

One thing did come out of all the reading: it’s generally a good idea to build your own power supply if you can. The commercial power supplies are, generally, over priced and it can be difficult to find one that exactly meets your specification. This sounds like a daunting prospect but trust me it’s not nearly as bad as you would think, a linear power supply only has a dozen components in it and there is no end of good information on the web about building one (in due course I’ll provide plans for mine).

Since I was drawing circuits I thought it would be a good idea to use an application designed to draw circuits. To my surprise I really struggled to find anything that I felt really fitted what I wanted to do. I’m sure there are very expensive commercial products out there that would do what I wan’t but that’s a sledgehammer to crack a nut. Eventually I came across an open source project called KiCAD which is an electronic design automation tool. The interface is, lets just say, unusual but once you get your head around it the application works well enough. KiCAD is really designed for laying out circuit boards but it works well enough for linking together large components e.g. BOB’s, drivers, steppers, etc.

If you are planning on trying out KiCAD I suggest you have a read of this page on making schematic components. It’s very unlikely that the components you are building your CNC from will be in any existing library. Once you’ve got your head around how to draw new components though it should only take about an hour to draw all the parts of your CNC (I’ll link to my custom library in a future article).

To keep you goind for now though here is some light reading about the various parts:

  • PMDX-126 V1.8 Manual – Version1.8 of the manual which covers revision C of the board. You are probably better off getting this straight from PMDX.
  • PMDX-107 V1.2 Manual – Version1.2 of the manual which covers all revisions of the board. You are probably better off getting this straight from PMDX.
  • CNC4YOU 60BYG301B Steppers – Data sheet and wiring diagrams.
  • AM882 Stepper Drivers – Version 1.0 of the manual. This can be found on the Leadshine website but it takes some digging. It seems they are phasing out the AM882 in favour of products that are built specifically for their steppers / servos.
  • Huanyang VFD – Covers all the Huanyang VFD models (the most popular DIY model seems to be HY02D223B). There are a couple of different manuals available online but this seems to be the most up to date and relevant for the VFD’s that are currently shipping. In particular there is one on CNCZone that seems to be aimed at older models as the main power connector arrangement is different.

If you are like me then you’ll probably also need to read these to understand many of the terms in the manuals above:

  • Transistor – You need to understand this to understand…
  • Bipolar Junction Transistor – Used all over the place, for example the connection between the BOB and the stepper driver.
  • Open Collector – Used all over the place, for example the connection between the BOB and the stepper driver.
  • Parallel Port – Having a bit of an understanding of how the computers parallel port works is very useful. In particular study the pinout table towards the bottom of the page.