Building the Robot

For full list of required parts see the Part List.

The Robot Arm

Build the arm as per the instructions provided in the kit.

The Track Base

The base was not an off the shelf kit but was instead assembled from parts provided mainly from Tamiya. I wasn't entirely certain whether it would be suitable. Tamiya make a single track tank base kit but this was not wide enough to accommodate the arm.

I have had issues with the tracks sometimes coming off when the base is rotating on the spot (although I have improved this - see later). However it works and its much cheaper than many of the other tank chassis available on the market.

To construct the track base, first build the two motor gear boxes. There are three ratios to choose from. I have used the the lowest ratio (203:1) will give the tracks more torque. This is the slowest speed but suitable for this kind of slow moving robot.

Dont worry at this stage about the position of the main shaft because this will be adjusted later. 

Use the bots included the Universal Plate set to attach the two gear boxes. They should be attached 6 holes in from the rear.

Attache the front axle brackets 5 holes in from the front.

Attach the wheel brackets underneath the main plate as shown below:

Now the wheels and tracks can be attached. The sprocketed wheels are attached to the gear box hex shaft.

At this point adjust the gear box hex shaft position so the the front and rear wheels are aligned. Rotate the shaft until the grub screw in the gear hub is visible, looses and adjust length.

Use all the lengths of track supplied to make four track loops. Loop the tracks onto the wheels.

The hex standoffs can now be attached, one in each corner. If using the screws as in the parts list, use one of the bolts as a spacer.

DC Motors

Solder two wires to each motor and color code the cable so they are easily identified. I left the cable quite long so that there's enough slack to remove the top plate without having to disconnect.

For doing maintenance to the base, the DC motors can be slipped out of the gear boxes. This allows you to leave the cable in place on the motors completely detaching the base from the top.

Attaching the Arm

Using spare screws from the Universal Plate Set, the arm can be bolted to the plate. Pre drill two holes in the front feet for the bolts to go through.

The USB cable for the arm is longer than it needs to be so coil it up and attach to the top plate using wire or tape leaving enough length to connect to the PI.

Power Supply

The gap between the bottom and top plate can be used to house the battery pack for the Pi. I found there wasn't quite enough space to fit the motor power supply in betweeb the plates so this is mounted along side the arm,

A short (15cm) micro USB cable is used to connect the battery and the PI.

Assembling the RTK Motor Controller

Full instructions for assembling the RTK Motor Controller is included with the board.

Lego Pi Platform

I used various lego bits to assemble a mount for the Pi. Lego is of course great because you can prototype different positions and layouts. 

Alternatively, hex stand offs and more plate sets can be used to create a platform. 

The lego pieces are attached using a lego piece shown below:

By chance the shaft fits into the holes in the Universal Plate Set. This allows a cross piece to be attached. Into the holes a lego axle is inserted and then connected to round axle receiving pieces that the platform can be mounted on:

This picture also shows the DC motor wires attached to the RTK Motor Controller going through the holes in the universal plate.

This rear shot shows the lego platform and the cables taped together under the top platform.

The Pi is attached to the play using two left of plastic motherboard pegs which are glued to two lego 2x2 squares which can be seen in the picture below.

I tried to minimise the amount of glueing at all stages so that it was easier to prototype different configurations.

Make sure you leave the Robot Arm on/off switch exposed.

The battery pack for the DC motors is mounted on the side.

I'm using a model B so there are only two USB ports which is just enough for the WIFI dongle and the Robot Arm USB cable.

Issue with Tracks Coming Off

Unfortunately, when the robot was doing a full rotate, i.e. one track going forward, one track in reverse, the outside track going in reverse had a tendency to come off. This was minimised by making sure the wheels were all in line. I also stapled the tracks together the tracks which helped. Also using the spare small sprocket wheels in the wheel and track set for the outside bottom wheels have also helped.

It might be that this configuration cannot deal with the weight of the arm. Any suggestions of how to improve this are gratefully received.

Camera Mount

The camera mount is made by attaching a lego hinge to the camera mount. The hinge is then attached to a piece of lego that is glued to the arm.

Summary

I hope this is enough to get you going building a robot controlled by a Raspberry Pi. The Tamiya kits are great low cost educational kits however, they are not as robust as some platforms and this robot may be pushing it to their limits with the weight of the robot arm.