My first play with a PicAxe controller and a servo based robot.
The first place to start is here: PicAxe.com
Well, actually this wasn′t the first place I started. Firstly I spoke to a friend Dave White who explained the different Picaxe controllers, showed me some code and then proceeded to build me a board and populate it and do some initial basic coding.
The wheels were machined from 3mm thick aluminium sheet and the diameter is too big for my Hobbymat lathe so I had to use a mandrel that bolted to a hole in the centre. The plate was then pulled back against the 3 jaw chuck with the larger outside jaws fitted to maximise the radius of support. A small groove was machined in the outer rim to give a location for the tyres.
Drive is provided by two servos, I bought the servos as continuation rotation ones – this means that you can set a direction and speed and they just rotate, saves the messing around and they were only £5 each on ebay.
The servos were mounted back to back on 6mm thick cross-beams. The servos are fixed with screws direct into the wooden frame, to make these fixings robust: the holes for the screws were drilled, the screw wound in and then back out and then super glue was placed in the holes and allowed to dry thoroughly. This then gave very secure fixings.
A bumper beam that pivots freely in the centre is at the front of the robot. Two small micro switches are located to the left and right of the beam and are activated when the robot bumps into something. This trigger is then used to stop the robot, activate reverse and to give a differential speed to the wheels so that the robot turns whilst reversing.
This means that when the robot continues forward it is on a slightly different heading from when it originally hit the object.
The brass beam adds to the “steampunk” look of the vehicle overall.
The battery pack is hidden inside a fake boiler, this cover locks into a groove and the copper pipe locates into a hole in the back of the main body.
The brake lever is a piece of brass drilled to fit over a small switch and glued in place with a small amount of epoxy.
Sadly the steering tiller is fixed, maybe in a future version that should move and the operator of the vehicle should be automated as well – now that would be interesting.
The wings were made from walnut with thin ebony guards over the wheels. Sitting on top of these are the port and starboard lights.
For the lights I bought some small test tubes: 50mm long and 6mm outside diameter.
The wire you can see in the test tube is enamelled copper wire that has been wound around a screwdriver and to get the shape. The wire was then pushed into the test tube.
An LED was then machined down to 4.5mm OD and glued into the end of the test tube using 5 minute epoxy.
These test tube are quite fragile and I must admit to being a bit concerned if I break one on the model as I will need to remove the wing and then the housing that the test tube was glued into.
Another admission is I did not have any green enamelled wire and so used blue with a green LED on the left hand side and red wire with a red LED on the right hand side.
The seats consist of a piece of machined wood on the bottom that was then covered in rubberised cloth – this was stuck down using evostick.
The back of the seat is made from 1.5mm plywood, again covered with the red rubberised cloth. The top curved beam was cut from 3mm thick walnut and then glued onto the top edge of the plywood.
You can just make out a nail in the curved back at the lower corner that I used to hold the plywood firmly – I pre-drilled a 1.5mm hole and then fixed the nail into the hole using instant adhesive.
The LDR′s were fixed into brass hexagons that are fixed to the main body of the robot using brass tube. The LDR (light dependent resistors) are arranged to detect light on the left and right hand side and then move towards the brighter side. A random element is added to this to make it more interesting. If you turn the lights out and point a torch at the robot it will follow you.
Sometimes it is great to build the fun parts and so I thought the person needed a hat. If anything it needed to be a tall hat made from tin plate.
I rolled up a piece of tin into a cylinder, flanged the two edges so that they clipped together and then made the top of the hat and pushed it into the cylinder. The bottom was simply a circle with a hole punched in the middle.
The edge of the hat was worked with a pair of pliers and then lightly sanded to give a smooth edge. The hat was soldered together by holding the hat in a flame and getting it hot and then applying lots of solder. After cooling the hat was then sanded to remove the sharp edges and any odd bits and then buffed using a fine brass wire brush.
I’ve included the code for the robot in it’s basic form on the next page.