Phoebe’s new frame

Sorry for the lack of updates recently – I’ve been testing longer term drift suppression primarily through horizontal velocity PID d-gain tuning.  It’s definitely improving but not yet to the extent that it’s worth reporting on.

So instead, I present you with the revised version of Phoebe.  What do you think?

Phoebe's new frame

Phoebe’s new frame

Lithium Ion Battery Power

All of my headless projects use Lithium Ion batteries.  These are made up of 1 or more battery cells which each produce 3.7V and potentially many amps in a small, light package.  Their only downside is you need 5v to run a Raspberry Pi, and so need to add some form of regulator.  My three projects have 3 different power requirements, and use 3 different regulator circuits which I thought I’d share:

  • Turtle needs a 5V supply able to supply up to 3A for the stepper motors.  This means starting with a 2 cell combination delivering 7.4V.  However delivering 7.4V at 3A means 2.4V (7.4 – 5) @ 3A is wasted as heat – given it’s a recharchable battery, I don’t really want that level of waste (nor heat melting the Lego Turtle!).  So the turtle uses a low drop out, switched mode regulator LM2596T-5.0 with the circuitry as suggested by the data sheet (a schottky zener diode, a couple of electrolytic capacitors and a 33uH 2.5A inductor).  This has proved perfect in all but one respect – the LM2596T has 5 pins packed into a TO-220 package – that means the pins are closer that the standard 0.1″, meaning they need to be bent carefully to fit.  I broke one doing so, so caveat emptor!
  • SkySpy has an 11.1V LiPo (Lithium Polymer) battery to supply up to 30A to the blade motors.  So the low-drop out is not needed in this case, but since the drop-out is now 6.1V at up to 1A for the Raspberry Pi, I still don’t want to waste the power; once again another switching regulator steps in: 78SR105HC. this one is not cheap, but it’s efficient, has only 3 pin (like a TO-220 plus heatsink) and lies flat on the breadboard which is critical when you have helicopter blades whizzing round.
  • Finally for the SkySpy controller, this is using the same battery as the Turtle, but doesn’t need anything like the high current, so the wasted power will be minimal, so I’ve gone for a non-switched regulator (LM2940T-5.0) which has feedback circuitry to minimize the loss in high drop out situations

All of these came from Farnell as always!

To infinity and beyond!

But where exactly to go next, now that the TurtlePi is essentially rolling on command? I’ve got some lego tinkering and some polishing of the python to do, but that’s it. Or is it?…

  • I’m starting to build up a order with my favourite electronic suppliers to assemble the electronics necessary for home grown voice / speech recognition, so I can boss the turtle around verbally
  • I’d considered Quadracopters as my Pi in the Sky project, but that’s living up to its name requiring cashflow.
  • In the meantime, I seem to have acquired an excess of RPis so I’m waiting to see the Pi Screen for use as a portable media player; the other as yet has no role to play.

For the moment though, it’s voice recognition using a 12 bit ADC, via the SPI bus to the Pi, and then all I have to do is to invent my own version of voice / speech recognition algorithms. Voice first (who is talking?), and then speech (what are they saying?). Certainly the latter will likely be dictionary based upon teaching / caching the Turtle commands for everyone who wants to use it. But first, I want to get the electronics and SPI bus working – that’s the stuff I love most.

Finally, when I finally finish fine tuning, I’ll see if I can get a video up here.


It’s alive!

I’ve been fiddling for the last couple of weeks now, on and off, playing with my 25 year old Lego (thanks Mum & Dad for saving it for the grand-kids – I’ll let them have it once they’re old enough!). I’ve been using Lego kit 8860 which is Lego Technic kit (no longer available, I think) which amongst many other things built a car chassis with steering, gears, adjustable seats, and engine with moving pistons. The Turtle luckily was much simpler…

The only fiddly bit really is how to attach the motors with 5mm shafts to the lego “+ shaped” shafts.  Proto-pic do an adapter for 3mm shafts, so I have a couple of those, so I just needed to carefully drill them out to 5mm.  One of the few times in my life I wished I had a lathe!