Android 4

The last Android, ‘Discotron’ works ok – it walks in a ‘fairly’ stable manner but was very slow. It is also ‘statically stable’ which means it puts all it’s weight over one leg very slowly and can lift the other leg off the ground – then stop like that. When a person walks they don’t lean over nearly as much, putting the opposite foot back down on the ground before falling.

This is called being ‘dynamically stable’, or a ‘dynamic gait’. In order to realise this in a walking machine, it must be able to move a lot quicker but still be strong enough to support it’s weight on one ankle.

For this reason I have used pneumatics for this android, it will swing it’s weight onto one side and step with the opposite leg a that exact time. The ‘natural swing’ of the android should enable it to walk like a human without leaning over nearly as far as it would to balance on one leg and stay there.

So far, the legs are the same length as mine…

I purchased some cheap pneumatic cylinders from an educational website along with a foot pump adapter, a special top for a plastic drinks bottle and a manually operated three-port valve:

I constructed this test rig with one cylinder to see how strong it would be. I am using about 2 bar (~30psi) as the cylinders are plastic and I don’t want them to explode. Even at that pressure one cylinder is too strong to for me to hold in with one hand:

Eventually I will buy a pneumatic compressor for around ?70 with a 2 gallon air reservoir, however for now the foot pump and the drinks bottle will have to do.

The Android itself is based around the last design with parallel tubes in the top and bottom of it’s legs, thus simplifying the design:

It can lean to one side, both legs are attached together right at the top above the hips, with the hips as a lever point. This means the legs cannot move sideways in opposite directions, but the legs can still turn independently so it can turn on the spot or walk around corners.

Each half of the leg will have two cylinders to drive it (both ‘pushing’ together), the leg will only be bent in one direction, or straight. This is still sufficient for it to walk with smallish steps. Bungee cords will pull the leg straight when the pressure is released:

I need to purchase some more cylinders and valves. The valves will be driven by radio controlled servos as this works out around 3 times cheaper than solenoid valves – this will be fine for low pressure work.

There will be four more cylinders on the legs – two on each ‘bottom section’. There will also be one either side between the inside of the knee and the inside of the foot – these will push the android onto one foot or the other.


After much thought and the discovery of some higher power 12v motors I have decided to convert this android to electrical power. There are the motors which are more than strong enough to move the android even though it is made of wood and steel. They are windscreen wiper motors:

They are quite large so I have to replace one of the steel tube sections with a new box style thing in each section of the leg. The bits of wood:

They will be arranged like this with the motor in the middle:

The middle section is the motor mount:

Here are the four sections all finished:

And here they are attached to the android, the front tube sections have been removed:

This is the back view, the windscreen wiper motors can be seen in each of the four sections:

I have used the original rotary levers and rods to move the each leg section – these were from the windscreen wiper assembly:


So, I have done quite a few things to this android since discovering the windscreen wiper motors. I have built most of the upper body structure, it has a motor to lean left / right, a motor to turn each arm and car door central locking motors to move each arm in and out:

Here the ‘workings’ can be seen, the motor right at the top operates a lever that pushes the hips side to side – this is currently just the right speed and power to lift each foot off the ground in turn and the android actually moves along (backwards and with very small steps) when the motor is powered up. The motors in the middle of it’s back are to operate the arms on levers to the shoulders:

The ‘spine’ in the centre of the body is at an angle leaning backwards – this makes space in the ‘chest’ of the android for the electronics (and a nice control panel etc). So altogether it looks like this, it is 1.60m / 5’3” tall (without it’s head):

Next will be the lower arms and some sort of grippers, also a start on the control electronics – this will be based around switches and relays – it will be very simple and may even use 555 timers to control the gait.