Author: Chris Lawton

After learning the lessons of my previous flight (http://blog.smfc.co.uk/2014/07/fpv-on-a-new-glider-in-the-wind/) and with Scott kindly donating a Super Cub to the cause I have now fitted the FPV equipment, GPS and OSD.

Firstly I removed the brushed motor, speed controlled and unfortunately the receiver since this is a single unit, and because I don’t have a battery with an EC3 connector, or an adapter.

Replaced this with an AR400 receiver, 35amp brushless speed controller (top right of the picture below) and 1300 kv brushless motor with a 8×6 prop.

Then mount the GPS unit on the back of the plane behind the main wing, this gets 5v power from the receiver. The OSD (on screen display) unit is mounted to the side of the fuselage (bottom left of the fuselage cavity in below picture) behind the 5.8Ghz transmitter (bottom right), and the antenna of the transmitter being on a flexible stalk will fit over the side of the fuselage to be tucked under the main wing. The FPV and OSD both get their 12v power from a jst-xh connector connected to the balancing connector of the main flight battery. The DORA unit (in the centre, but not visible) also plugs into the receiver and the OSD to display the RSSI (Received Signal Strength Indicator) on the FPV screen.

Finally the wing goes on and the camera on top

all ready for a test flight

Well after a little problem with the E-Fair, I’ve put the FPV equipment on the Minimoa glider and took it up for a bit of a test today

http://www.youtube.com/watch?v=3NVf5Imvuec

Apart from the wind which at various points took the glider most noticeably at the start of final approach and just before touchdown, I think I had the camera mounted pointing a little too much down, although I thought through the goggles I was flying quite level I was flying with a lot of up elevator and was told the glider looked very tail heavy.

Secondly EPP foam seems to block GPS signals much more that I expected it to, since it never acquired a GPS lock. I was hoping to check the home position and test the point to home functionality of the CL-OSD update which I flashed to my mini-osd unit, but since a GPS lock was never acquired the home position could not be set.

Also the 5.8Ghz transmitter antenna was fully enclosed in the plane. Again EPP must interfere with 5.8Ghz a reasonable amount since I wasn’t anywhere near as far away as I was with the E-Fair (with the antenna poking out under the wing) and the signal was breaking up far more.

So in future, the FPV antenna should be outside the fuselage of the plane, as should the GPS receiver unit (at very least to obtain an initial GPS lock), and I need to check the horizon position on the screen when the plane is level on the ground.

I recently purchased 2 Turnigy receiver controlled switches, neither worked. I searched for alternatives and could find none, but I then found a post on another blog that suggested using a servo, and turning the pot so that the power is off when the switch on the transmitter is in the ‘off’ position. This seemed like a great idea, but I thought I could improve on it a little and effectively make a switch which worked in the way that the Turnigy switch should. So I did and for anyone that is interested here is how it all works and how I made it.

First thing to do was to take apart a servo, we don’t need the plastic bits, gears or motor

Take the top and bottom off, the motor and the control board come out quite easily and the gears come of the top with a bit of persuasion.

 To get the pot out I needed to smash the plastic casing

Next step we need to cut the motor from the circuit, but we want the wires so cut it as close to the motor as possible

This leaves the controller board and the pot. I have also trimmed the shaft of the pot since we only want it to set the center point of the switch, once this is set we don’t want it to change.

So now we think a little about how the servo works. The servo is (was) made up of the 3 components, the controller board, the potentiometer and the motor. The potentiometer is connected to the arm connector and is used to tell the electronics board were the arm is. The board is then fed the signal from the receiver which tells it where the pilot wants the arm to be. If the arm is actually to the right of where the pilot wants it then the board will spin the motor to the left to move the arm to the left, if the arm is to the left of the motor then the board will apply a reverse voltage to the (brushed) motor and spin it to the right, if the arm is in the right place then no voltage will be applied to the motor. So if we move the potentiometer to the central position then when we move signal to it above and below its position we will get a positive and negative signal. See the following 3 pictures, the contraption is connected to the elevator channel, and I have connected a voltmeter in the place of the motor. When the elevator stick is in the central position we see zero volts on the voltmeter. When we move the stick down we see 3V on the meter, when we move the stick up we see -3v on the meter.

We only want the switch to work in 1 direction so we can use a diode so that current will only flow in one direction, in this case I decided to use an LED (Light Emitting Diode) this works as a diode and also works as a signal to show if the switch is on or not. Before you solder the LED on its worth trying the LED each way round so that you can make the switch turn on when your switch is in the direction you want it to be on, if it is on in the off position (if that make sense) simply turn the LED round, then solder 1 leg. (This was the LED which I purchased for this http://www.ebay.co.uk/itm/271457390406?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649  they are significantly cheaper if you can wait for them to come from China such as http://www.ebay.co.uk/itm/200972608918?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649)

This now should work as a switch but will only be able to deliver about 500ma at about 3v (maybe 5v maximum since this is the receiver voltage), but I wanted to ensure that this would allow me to switch more power, so I also connected a relay switch so that the LED and the relay are in series on the output of the servo board. I purchased this relay www.ebay.co.uk/itm/351041618488?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649, RS and other suppliers will supply suitable relays, a non latching relay with a 3v nominal coil is required. I found that the LED connected in series created too much of a voltage drop and failed to activate the relay correctly, so I removed the LED and found that this relay is actually polarized so it works only in 1 current direction so the diode was not necessary, I then initially connected the LED in parallel to the relay as an indicator, using the Normally Open connections on the really I connected the JST plug and the load connection.

 

This is now ready, a bit of packaging with some insulation tape and its all good

 I actually thought that the LED was causing a further problem, so I removed it, but it turned out that the pot position had moved which was causing the problem, but this now all works nicely giving a full 12v output on the connector I attached when the switch is activated.

 

 

There is a lot of information here that you don’t really need to make the switch from a servo, so in summary what you need to do is:

1. Remove the controller board, pot and motor from the casing, getting rid of the gears.
2. Cut the motor away
3. Connect the coil of a relay switch to the motor connections (the direction determines which throw direction the switch will be on at)
4. Use the Normally Open connections on the relay output to connect your load and power source.

 

I hope someone understands this and finds it useful.

 

Update:

The relay that I listed here is rated at 2 amps switching current, it is double pole, I only used 1 pole and using it for the rocket igniters did blow the relay contacts, so if you are using this relay then connect the 2 poles together to give a better rating, or use a different relay such as this one:

http://www.ebay.co.uk/itm/251487355244?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

rated at 10amps switching current @125v but they are larger than the other ones.