Building a PICAXE controlled rover

P1250840I’ve already shown how a PICAXE can be used to build a simple Robot. I know that this blog is really meant to be aimed at Raspberry Pi users but the techniques would be similar. As a result, I thought it’s worth uploading the photographs that show the robot being constructed. If I can get the technical Lego back from my son, it might be possible to rebuild using the Raspberry Pi, and even extend the functions to make more of it!

The original blog post shows the robot in action.

Chassis parts

The chassis is constructed using a variety of beams and plates along with a couple of gear trains. You’ll need:

  • 8 x 1 beams (4x)
  • 8 x 2 plates (1x)

Chassis parts

Chassis beams

Once the chassis is assembled, it’s time to start putting together the gear mechanisms on top.

P1250898Grab a couple of 24 tooth spur gears and axles ready to build the worm drive mechanism. You’ll need some narrow spacers to keep things in line but it’s all pretty simple.

P1250887The worm drive with a 24 tooth spur gear ready to drop onto the wheel drive gearing.

P1250897

P1250896 24 tooth spur gear used as a “wheel” to complete the worm-and-wheel mechanism. This will give a reduction of 1:24.

P1250895 Fit the wheels on to the end of long beams and add plates on top to keep it strong.

P1250894Assemble the wheels and beams to the main part of the chassis. Remember to tuck the axles carefully into the chassis and check that these rotate freely. You may need to adjust the position of the wheels to help this along.

P1250893Extend the size of the chassis with plates.

P1250892Create a front skid using a small rounded spur gear and an axle.

P1250890Gather the parts to link the chassis together and provide support for the next layer.

P1250888

P1250886Add in the worm mechanism created earlier. You will find that the wheels can be tested by now gently rotating the higher of the 24 teeth spur gears. Repeat the check for free-running.

P1250885The standard Lego motors are rated at 4.5v. A couple of volts seems to be lost across the output transistors in the motor driver so it’s safe to use a higher voltage power supply. Add 24 tooth spur gears to the motor shafts.

P1250884Fit the Lego motors and prepare to start joining the chassis together using various plates. The overall speed reduction is based on a worm/wheel mechanism (1:24) combined with a simple spur gear mechanism (1:3). The overall reduction is therefore 1:72 which seems adequate for this weight of vehicle.

P1250883Build up the framework so that a platform can be easily fitted.

P1250882

P1250879

P1250877This platform will support the PICAXE motor driver board. It’s also big enough to fit a Raspberry Pi.

P1250876The blocks at the end are used to ensure that the battery pack doesn’t wobble around too much.

P1250875Create some bumper switches using lever arm microswitches and blu-tak.

P1250872

P1250860The LDR modules are easily made with a 2×2 block, a 2×2 plate, a 5mm drill bit, some wire and a hot glue gun. These can be used with the analog inputs to aid navigating around a black line drawn on the ground.

P1250859Fit the LDR modules to the bottom of the plate carrying the bumper switches.

P1250857Here’s a simple push button created with a 2×2 block and plate with a long shaft 5mm tactile switch. These work really well for sending on-off control into the PICAXE

P1250854The light module is created from a Superflux LED embedded within the 2×2 block. There’s also a 180Ω resistor hidden in there. The transparent blocks spread the light out a bit more and the cap makes a really pleasing looking light. I’ve used it in the final model to indicate that it has bumped into something.

P1250847The overall wiring for the PICAXE motor control board. There are two pairs of cables for the motors, one output for the LED, two digital inputs for the bumpers and two analog inputs for the LDR sensors.

P1250842

The finished PICAXE controlled Robot

Once the project is built, it’s necessary to write a control program. The algorithm is featured on the original page. I would suggest start by using just the bumpers and then work towards using the analog inputs.

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