Actuators
Home
Up
Motion systems
Actuators
DIY Motion platform I
DIY Motion platform II
DIY Motion platform III
DIY Motion Platform IV
DIY Motion Platform V
New ideas
Presentation FSCB

In order to make the platform move, each axis needs some type of actuator. These actuators can be of the rotational kind, where the actuator directly drives the pitch or roll rotation point, or the actuator is a linear travel type, that pushes the edges of the platform. The linear actuatorsí travel needs to be long enough to make the desired axis movement, and its force needs to be sufficient to push the platform weight with some speed. Quick response, accuracy, reliability and safety need to be considered.  The type of drive control is also important for interfacing the whole thing to the PC.

Hydraulic valves are mostly used where high forces are needed. They are normally not the choice for home-build platforms, since they require complex oil pump and driving systems.  

Pneumatic valves are easier to build, and can be successfully used for driving low loads. It is however more difficult to control their thrust and position accurately.   

Electrical linear actuators are becoming popular for driving motion platforms. They can be used for low to medium loads, can be accurately controlled, and interfacing is relatively easy, by using an analog electric driving system with positional feedback via a potmeter (servo control system). 

There are several options for home-build electric linear actuators:

 
Above a sketch of an actuator that consists of an electric motor that drives theaded steel shaft, over which a counter threaded cylinder moves in and out. These type or actuators are often used in CNC machines. The threads need to be specially made for this type of application, and normally cannot drive high forces, as they easily wear out. Industrial actuators of this kind often use ball-bearings in the thread (rollerscrew). The picture shows two types of actuators that (I think) are used in hospital beds. They are strong, but move too slow for our purpose.


An electro motor driving a gear box with lever is often used in small motion platforms. The gearbox and lever need to be very sturdy, as the forces on the lever and end gears are very high. On  http://www.jimspage.co.nz/intro.html  Jim has made a great description on how his platform works. With a 12V electric motor driving a car steering box, sufficient force can be generated for moving a small cockpit on tilting platform. It also has the advantage that there no problem with end-stops: The platform's travel is automatically limited.


The pulley driven cable method is shown above: It's relatively simple to build yourself, and can exert  quite some force. Some gearing may be needed, but winding a cable on the motor shaft can already be sufficient. Cable tensioning needs to be assured for this system to work well. I have used this system for Force feedback on the flight yoke , the DIY motion platform IDIY motion platform II and DIY Motion Platform III

Ian Hopper has designed a neat linear actuator for home-build motion platforms. For more info see http://buggies.builtforfun.co.uk/Sim/linear-act.html
  

 Back Next