Control System

**AppleBite** · Nov24-09, 12:33 PM

Hi everyone,

I'm designing a light-weight hovercraft (2 light fans, 4x1.5 V batteries, 30x20cm in size). It needs to travel 6m straight ahead, then make a 90deg turn to the right and travel on for another 2m.

The problem is that the craft must make this turn ON ITS OWN, meaning that there can be no external control system on it. The control system can be either electrical or mechanical, but weight will pose a serious problem for any design.

Are there any good engineering minds out there with some good ideas of a simple, light-weight but still effective design of such a control system?

Cheers

**berkeman** · Nov24-09, 01:55 PM

Originally Posted by AppleBite

Hi everyone,

I'm designing a light-weight hovercraft (2 light fans, 4x1.5 V batteries, 30x20cm in size). It needs to travel 6m straight ahead, then make a 90deg turn to the right and travel on for another 2m.

The problem is that the craft must make this turn ON ITS OWN, meaning that there can be no external control system on it. The control system can be either electrical or mechanical, but weight will pose a serious problem for any design.

Are there any good engineering minds out there with some good ideas of a simple, light-weight but still effective design of such a control system?

Cheers

What actuators are you using to control the direction? Do you already have a gyroscope as part of the system (at least in yaw)?

**AppleBite** · Nov24-09, 02:40 PM

We have no gyro on the system. The craft will be driven by the primitive mechanism of two fans; one horisontal (providing vertical thrust), and one vertical (providing forwards motion and potentially vertical thrust by use of an air divider). The direction will further be determined by rudders behind the vertical fan.

What we need is a way of turning these rudders and hence the craft after it has driven a distance of approx 6m.

**berkeman** · Nov24-09, 02:46 PM

Originally Posted by AppleBite

We have no gyro on the system. The craft will be driven by the primitive mechanism of two fans; one horisontal (providing vertical thrust), and one vertical (providing forwards motion and potentially vertical thrust by use of an air divider). The direction will further be determined by rudders behind the vertical fan.

What we need is a way of turning these rudders and hence the craft after it has driven a distance of approx 6m.

I'd use a small DC motor with a worm gear to actuate the rudder. You could do a simple timer circuit to generate the control signals for the DC motor (forward and backward to move the rudder left and right, for example). You would have to tune the timing to give you the distances and 90 degree turn that you want.

It would be much more precise with some kind of closed-looop direction control -- even just a compass or something...

**Mech_Engineer** · Nov24-09, 03:34 PM

I would recommend using two fans side-by-side in the middle of the craft for horizontal thrust, because you can also reverse one of the fans to achieve a zero radius turn.

As for the track you're trying to follow, remember that for the hovercraft to make a 90 degree trun, you will have to reverse thrust to stop (assuming you're already moving), turn (hopefully using your pair of drive fans), and then thrust forward again. The hovercraft won't roll to a stop like a wheeled robot might.

Of course to stop you could always just turn off the lifting fan also...

**Bob S** · Nov24-09, 06:37 PM

Do you have an on-board microprocessor? I would use four fans, and use banking to move forward or make the turns. By reducing the voltage on the two forward fans, the craft will lean forward and accelerate, For banking, reduce the voltage on the port or starboard fans and the craft will turn.
How far above the floor are you? Can you use ground-effect lifting? Do you have to be more than a few mm above the floor? Can you put a reflective strip along the floor that a photocell on the craft could follow?
Bob S