Hi.
There is more complexity to it, as the goal is to attach a 5mW laser diode (very lightweight) on top of a magnetic compass disc, probably flooded type and be able to change its aiming azimuth. All wirelessly.

In other words, I need your brains if can suggest a way to build this contraption. How would you do it ? A laser diode that can be lit and turned in azimuth attached to the top of a compass disc.

How to select the most convenient frequency to transfer energy ? Any mechanical actuator/contraption that could work ? A cell phone motor ?

 

As I understand cellphone motors they run continuously with an excentric load to produce vibration. How do you intend to use it as a servo motor to position the laser diode? I would look at hooby servos from Futaba. They work on a fairly simple PPM method.

http://www.futaba-rc.com/servos/digital.html
http://www.futaba-rc.com/servos/digitalservos.pdf

Not sure you can come up with a suitable wireless power transfer method. I'd break the problem into two parts and work on those parts independently.

 

I assume you know about hall effect sensors?

Why do you need to power it remotely, why not just use slip rings, assuming it must do multiple rotations?

 

Thanks PB.
No excentric load. Just the motor to somehow move the aiming azimuth. Or anything else.
Am now thinking that if that such motor has permanent magnets, may not work as it would deviate the compass aiming
Would have to be the anything else.

sirch2: How would you power not remotely being under a dome, on a moving disc ? Yes, I know about Hall sensors; can you elaborate how would you use them ? Slip rings would surely impair the compass disc movement.

The laser would beam towards a preset azimuth, regardless of a boat heading. Powering the laser wirelessly may be the simple part. The electromechanics of rotating it has me scratching my head...
External control would be - Power on/off (which would power the assembly and laser) and turn CW/CCW = 3 buttons
https://c1.staticflickr.com/5/4120/4778032914_061a4299e8_z.jpg

 

Would it be possible to put a mirror on the compass and bounce the Laser beam off it? I am no optics expert...

 

That was my original intention, 45 degrees mirror on the centre of the disc with an external laser aiming down from the outside. But it still needs rotating the mirror to preset to an azimuth. That is the hard part.
And the wave motion would vary laser incidence and reflection angles. So I prefer the whole contraption mounted on the disc.

Been also evaluating a substantial amount of focused infrared light to a solar or other cell on the disc for the powering part.

 

Could you use an electronic compass and use the output to drive a servo/stepper motor to position the laser?

 

Yes, that could work. But would need some brains I do dot have going that way. The electronic compass outputted signal would need a value added-sustracted from a laser azimuth servo sender feedback. I think.

 

I don't know what kinds of electronic compass elements are available out there but I think it would be relatively straightforward to achieve the processing you need within a small micro-controller or something more powerful like a Raspberry Pi; it would certainly be a lot easier than if you were to take the mechanical compass route.

Just spotted this:

http://www.ebay.co.uk/itm/GY273-HMC...al_Components_Supplies_ET&hash=item19f2bb7004

 

Thanks; will look into it.
Anyway, the laser wold have to be on a gimbal mount to maintain its horizontal aim at any heading, going back to wireless to power it together with setting azimuth. That is what the compass disc would achieve by itself.

The laser has to aim horizontally to a preset azimuth no matter where is north nor the vessel be heading.

 

There is no reason why the laser could not be held in a horizontal position by electronic means.

 

A Hall effect sensor is the the sensing part of an "electronic compass". As others have suggested you can use this with a microcontroller to drive the laser to the desierd heading. There are also IMU devices that give corrected headings - e.g. http://www.adafruit.com/product/1714

Would the weight of laser, etc not cause a magnetic compass to drag/bind and can you compensate for the magnetic effects of the laser and power supply.

 

Thanks. Will evaluate the option.

The weight of any attachments to a compass disc can be made neutrally buoyant, and with not much iron in them. Would increase its inertia/momentum somewhat, I think.

 

You missed my point about the cellphone motor. It is unsuitable because it has only one mode of operation, which is to run continuously at an uncontrolled speed. That is not what you need. You need a motor that you can command to go to a certain position and stay there. That is why I suggested the Futaba servos. They are light weight and easy to control.

I mentioned the eccentric load to explain the primary application of the cellphone motor. I agree that your load will not be eccentric.