Wednesday, October 13, 2010

The Work Continues...

Well, yesterday saw my first step into a larger world - I etched my first PCB(s). Normally, I'd just use experimenter/vero/whatever-board - when you're trying experimental stuff, it's easy enough to use. The problem with that stuff, though, is it's only for relatively low amperage. For driving motors, you need to be able to control reasonable currents... Assuming around 4-6 amps, I decided it was easier to make a small board to mount the MOSFETs which, for the uninitiated, will be the electronic switches for controlling speed and direction.

So what is called for is a couple of small boards, with big tracks - so I decided to make a couple of small boards, using Copper clad board, a special pen, and the required etching compound. Of course, manually drawing onto the copper (protecting the bit that I don't want eaten away) means that it won't be consistent, nor the optimal size... But I'm making this for myself, and just wanted something quick to do the job. Plus it's the first board I've etched - clearly a milestone.

Easy enough to do, but not an optimum result. What aren't readily visible are the bits that haven't been protected enough - but it's enough to do the job, especially when I give a coat of solder over the tracks to ensure good power transfer. It will be enough to control the power, give the MOSFETs something to be attached easily enough...

For those not technically minded, MOSFETs are a type of transistor made for switching high power - and hence good for running motors. For those technically minded, I've been reading up on Complementary Pairs - and how easy they seem to use in an H-bridge.

The end goal being that although controlling motors is simple enough, I want to not only have a good control system, but plenty of feedback to any control system - ie proprioception - available. So, experimental circuitry is being made and will be tested

I could probably buy what I want, but cost is a killer, and I'm learning plenty.

Wednesday, October 6, 2010

Droid with a good motivator...

My new motors arrived from Oatley Electronics on Friday... They're a bit heavier than they look - but hardly surprising when you think about it, really. Brushed motors, which means that they're not as efficient and won't last as long as would be ideal - but so much easier to drive than any other type, such as brushless.

They're 100W at 24V, so they'll put out a bit of power, while not needing too much amperage. Of course, it means playing around, and plenty of batteries in order to get the full power... On the other hand, because they are brushed motors, it will be possible to run them at lower voltages - and therefore lower power.

I've just checked from the standardised astromech plans (available online), and it looks like there will be plenty of room in the feet to fit them - the whole frame is about 5 inches wide, 3.5" at the top, while feet are 7 wide at the bottom but 3" or so at the top... What I will do is do up a paper foot to double check... If I have to fudge... I suppose it will have to be... I doubt any hobby builder would call me out about it - once you know how much work it is to do, you don't denigrate others... If someone does, I reckon that a couple of hundred watts propelling quite a few kilograms bearing down on them will change their minds.

The other step is to build a couple of motor driver boards - a few high power MOSFETs, a current shunt (to test for motor stall, etc., rotation encoders...

Wednesday, September 29, 2010

Now underway!

I've started building the dome - ie the head part. I'm building an initial full-size model out of paper, on the grounds that it's cheaper. Much, much cheaper. So, an hour or so spent with scalpel and rotary cutter have meant I have the beginnings of a dome.

It's not going to be the final version, but it's worth doing - if I end up going to a local plastic cutter to get the sheet styrene cut, if I can give them a DXF or DWG it will be easier.

So I've used a bit of mathematics to build 1:1 scale, flattened PDF versions of parts.

So I've got the top section cut out (at least one, I'll double layer it), and the mostly vertical bit of the head. Next will be the neck, and the body skins...

And on their way - two 24 volt, 100 watt motors, with a mounting frame and wheel!

Thursday, September 23, 2010

What is an R6 astromech?

We shall start off defining our problem... What is an R6 unit? Well, in the SW Expanded Universe (all the stuff outside of the movies and series), a lot like R2 - a bit more capable, the biggest difference is a different shaped head.

R6-D14, current colour scheme

The advantage with the head shape is that it's much easier to scratch build than is a hemispherical(ish) dome. And I find it a bit more aesthetically pleasing. Why is scratchbuilding important? Simple - money. Until I have enough money to throw around getting the top end equipment (like a machined aluminium inner frame), I'm going to have to make do.

So, at the moment, I trying to find ways to make do. A bit of searching, a bit of maths, and some talking online (thanks to Dan Stuettgen, builder of R6-D1 for his dome plans, I'd link to him, but he has no current website), a demo copy of Turbocad, and a couple of visits to a local retail store with a printery (that can handle printing A1 and A0) has lead me to having copies of the front and rear skins (of the body), and two of the head. At this stage, I've only put the hatches on the top of the dome in, will slowly get the other ones for the head done as I can.

The paper plans will eventually be used as templates for making a frame (admittedly, machined aluminium would be nice)... and paper with give way, either to more aluminium, or to sheet styrene. No guessing which will be cheaper, easier, and lighter, though. I might have to make do with wood for a frame...

For those of you who haven't guessed, this could be an expensive hobby... and I haven't started talking about what I want as the electronics inside. I'll give you a clue - not an empty, static display, and not radio controlled...

Sunday, September 19, 2010

In The Beginning...

So... after many... well, I have to admit years of wanting one, I am going to actually start making my own Astromech.

Firstly, the legal: The design is owned (as far as I know) by Lucasfilm... or whoever. It's not mine, is the main thing. The look of the Star Wars astromechs is copyright.

Secondly: Don't ask me to make one for you. For starters, I don't have the time. Additionally, you don't have the money that you would have to pay. Also, the fact that the design of them is patented means that the money would go to George Lucas, via the Clone Army of lawyers that would be launched. However - Mr Lucas has gracefully allowed fans (such as myself) to unleashed our creative and/or technical talents in recreating elements of the SW universe.

Now that we have that out of the way...

What strikes me is that the internal, electronic systems are an interesting (albeit potentially major) engineering project. The stuff beneath the shell is up for grabs - think of it as building a robot, except having an external design to adhere to. External sensors are limited (for the most part, I might have to fudge) to what can be seen, but under the skin has plenty of options open.

So - Why an astromech?

Simple. I'm a fan of the rotund 'bot. Yes, I know how much "personality" was not much more than puppetry, but they are an interesting design. Yes, using a set design makes it more difficult... but I'm claiming that as part of the challenge.