Saturday, 18 May 2013

The Bit Bang Theory : High torque encoded DC motors for robots from car window motors

Second hand car windscreen wiper motors are still the first choice for many robot builders. They are easy to use, easy to control and you can normally pick them up for around £15 each from scrap yards.
They are normally pretty manky when you get them and need so cleaning up.
My process is
  • Strip them down to bits, taking photos at each step.
  • De-grease the entire thing with petrol and a on old toothbrush. (Goggles, gloves, outdoor space and obviously no smoking people!)
  • Make sure that each electrical carbon brush is isolated from the case, and replace each feed wire with 5A flexible cable. Add a third earthing wire to the case, as close as possible to the brushes. 
  • Fit 100nf capacitors between the brushes, and each brush to the earth point, so that's 3 capacitors. If you don't do this the moor can generate high frequency noise interference which will attract the attention of all around you, including the authorities,
  • Grease all moving parts with SILICON grease, not mineral grease, that can damage the nylon parts apparently.
  • Re-Assemble
  • Clamp the wires to the case with two cable ties and test with a 12V source.
OK this might not seem easy, but I actually enjoy watching something new and useful being born out of scrap, however there is a problem. For most projects you need several motors, often in closely matched pairs for drive systems, but scrap motors come in all shapes and sizes, and getting two the same can be a challenge.

Window Motors

I looked at using window winder motors, because they come in pairs and will be perfectly matched, but here the axle is fixed to the chassis and the rubber drive wheel moves round it, which isn't quite what we need.
However I came across a really interesting article on "The Bit Bang Theory" blog which solves this problem by stripping them down and re-assembling them with a fixed axle. I f I can make this work then that will solve another problem, especially for smaller projects.
Check out the article at http://thebitbangtheory.blogspot.pt/2013/05/high-torque-encoded-dc-motors-for.html
and let me know what you think
[Via Hackaday]

Thursday, 16 May 2013

Instructables: Making PCBs

This appears to be one of the simplest, cleanest, easiest ways I have ever come across for making PCBs.
  • Print your PCB mask on white paper with a laser printer
  • Use an iron to transfer the design to a sheet of copper clad board
  • Soak off the paper backing
  • Etch
  • Drill
  • Clean
  • Solder.
If this works you could easily make a working PCB in under an hour, possibly even less.
I am about to make a MIDI to CV convertor for my synthesizer, and will definitely be trying this method. I will post the results here.