This article shows the steps I took to make a low cost linear actuator for Android 5 - 'Combotron'. Although it could have many other uses in robotic arms, legs or anywhere else where 'piston' style movement is required at high torque and relatively low speed.

I decided that the idea should be based around a nut moving up and down threaded rod as it turns. I started with some M6 threaded rod and some bits of wood:



I found these hex shaped threaded nuts that are for joining two bits of M6 threaded rod together. One of these will be my 'moving nut':



I made 5 holes in the bits of wood, inserted the hex nut into one of them and 6mm inside diameter aluminium tubing into the others. The outside holes are to hold 'rails' that the actuator will slide up and down on, the next two holes towards the middle are for the actuator 'push rods' and the middle hole is for the turning rod:

Here is the sliding part with the push rods attached:



and the rails. Fully in:



and out:



Here is the turning rod attached, it has 6mm locking nuts on each end so it is free to turn, as it does so the middle section moves up and down:



I plan to use cordless screwdriver motors as they are already high torque and only cost about ?4 (GBP) from my local household store:



However, this design is rather big and ugly, so I decided instead of 5 rods in a row, I would make it with them in a number 5 'dice face' formation, then it can be much thinner. For each section I decided to use large M6 washers:



the middle section has the hex nut inside a piece of wood held by a washer on each end:



This is much thinner compared to the motor, it is also mainly made of steel so it's quite strong:

Here are the two side-by-side:



I guess they both have their uses, I shall use the thinner design for the legs of Android5 - Combotron. The second design is also shorter as the washers are thinner than the bits of wood, but both designs have a travel of around 65mm.

The only thing missing is a bracket to hold the motor on, one end of the actuator could always be made of a larger aluminium piece to hold it.

05/03/05

Today I have built two actuators for use on the android. I have used slightly larger M8 washers and M8 threaded rod for the turning part - the rest is M6 rod. The washer that was nearest the motor has been replaced with an aluminium bracket to hold the motor.

The M8 rod has been filed down to a 'hex' shape to fit in the existing bit mount attached to the screwdriver motor: