Here's a bit of rambling on what I got up to with a Big Trak...
My aim was to build up from simply "not breaking it" to having an autonomous robot that could map it's surroundings using sensors - and preferably not run over the Mrs or the cat in the process
I'd never done any electronics (or been remotely interested) before I got my first Raspberry Pi - which went straight behind the TV running OpenELEC. Fortunately, that early morning frantic clicking session way back when paid off and I eventually had two of them
I started, as you do, by searching on the interwebs and finding guides to dismantling - like raspberrytorte
Didn't take too many pictures early on. I'll do better in future
This is a "V2" Big Trak - got it from Maplins and the first one was DOA (well, 50% DOA in that only one drive wheel drove
) Maplins replaced without any fuss - I'd been told they do that, never bought anything from them before though. I went for the option of removing "IC2" (you can see the black blob on the circuit board above) and that worked (knew I'd eventually need the heat gun I bought years ago and had never really used
). That led to me also removing several of the surface mount resistors at the same time - no big deal. Then I then went to solder a wire to one of the IC pads (aiming to follow the raspberrytorte idea of partially using the original circuit board) I gave it a good tug to check my soldering - some of you know where this is going already, don't you
. Yup! That left me with circuit board and a piece of wire with a pad attached to it - nowt wrong with my soldering then
Next was to build an "H-Bridge" so Google led me to a post by Chuck McManis
. Off I went to the RS website and the very next day I got all the bits I'd ordered - lots of bits given the minumum ordering quantity (each one was very cheap though
). Then I discovered that translating the H-Bridge schematic onto stripboard was not at all trivial, to say the least . After a day of grief I have to admit that I just gave up and bought a TB6612FNG motor controller for a few quid from Proto-Pic
who I've used a lot and seem to have a very good range, very impressed with the speed of delivery and quality of service too (standard disclaimer: I have absolutely no connection with them apart from being a very satisfied customer).
Now for more pictures...
Checking out the motor controller on a breadboard (seemed sensible to me)
Stripboard motor driver all assembled in the BT
By this time, I'd spoken to a mate who knows about re-chargeable batteries and he'd pointed me to something that would be easy to use (easy to use, not necessarily "good" was the objective so a sort of iPhone USB 5000mAh cheapo thingy from eBay - he described it as "numpty friendly"
). Motors driven by 3 Maplins Hybrid "D" cells (in original battery compartment), then 5 (hot glued a 2xD cell box to the back) then 4 on the grounds that I could ony recharge 4 at a time.
Despite never having heard of them until getting the pi, I now have a couple of Arduino boards (well 2 x Uno, an Uno Pro Mini, a couple of ATMega 328Pu's and some ATtiny's - I seem to like Arduino
) I decided to drive the motors and everything else from the Arduino and let the pi do "command and control"
By now I'd added an Edimax wifi (with antenna, it's a tank, got to have an antenna
), acquired an HMC6352 compass module and some HC-SR04 ultrasonic range finders. I had a lot of traction issues with the BT which was solved by wrapping several elastic bands around each drive wheel.
Here's a shot of some testing on my desk
Ultimately, I don't think I spent enough time thinking ahead - the wiring became a real mess. I rushed all the software (bodged together bits of Tcl - not even doing what I know justice really) and when I came to try to control it though my cobbled together web interface it really wasn't very good.
Here's a video of it in action (before the final sensor fitting)
I'm not very good at video - all you'll see at the point where wi-fi drops out and it disappears to crash is my shredder and my left big toe
I've given up on this now - made too much of a mess with the wiring. The Edimax wifi was crap - ended up swapping it out for their nano adapter which is absolutely bullet-proof (to be fair, the antenna one is too if you don't use the USB extension cable bent through 90 degrees and stuck on top of a plastic toy with hot glue). My ultrasonic sensors and compass stopped working (I think I cracked the bits of stripboard I'd used) and I removed my stripboard with the motor driver on it and cracked that too. I've had enough of stripboard - it's not for the ham-fisted
The Adafruit perma-proto stuff is much better and stronger and I'll be using that in future (it's not cheap but given the amount I'll be doing it's not a problem).
My personal Big Trak project is now over. I've learned a lot (well, not hard from knowing nothing
) and I've already taken delivery of an inexpensive 4WD platform (the Seeedstudio one, $51 delivered from China
). More on that later (and hopefully in short and interesting posts, rather than this one