Projects – Page 2 – Solihull Model Flying Club (SMFC)

FPV on a new glider in the wind

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.

Turning a Servo into a Remotely Controlled Switch

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:

Remove the controller board, pot and motor from the casing, getting rid of the gears.
Cut the motor away
Connect the coil of a relay switch to the motor connections (the direction determines which throw direction the switch will be on at)
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.

3…2…1… Launch!

First test launch of the rocket glider.

3…2…1…

https://www.youtube.com/watch?v=BVycHil999A

OK, the wind has moved round a bit, so move round, change the angle of launch, change the position of the rocket motor slightly on the glider.

3…2…1…

https://www.youtube.com/watch?v=uJm2YH2K2K8

Hmmm, still needs a little something.

Dusters maiden and Prop Selection

I recently finished the FT Duster, I’ll not go into the build since the video on Flite Test goes through the build so much better.

http://flitetest.com/articles/ft-duster-build

The maiden flight could have gone much better:

http://www.youtube.com/watch?v=l4SJHfTz_IA

I reduced the throws slightly and increased the expo a little more, reduced the size of the battery I used from a 2200mah to a 1400mah 3 cell. At Mels suggestion I also removed the cab. All this moved the COG slightly back so it is on the back side of the spar in the wing.

I don’t have a video of this, but this made it a much easier plane to fly, still a little twitchy and under powered but much better.

So I then decided to pick a better prop I had a few to choose from:

from left to right an 8×4.5 triple blade, a 6×4, and 8×4 which was on duster for its maiden, an 8×6 orange, and 8×6 black and a 9×5 orange prop. I then setup Duster with an amp meter and anchored it through a set of scales to give some idea of the thrust generated:

Although the measurement of the trust is by no means perfect it should give some idea of how good each prop is. The motor that is in duster is a 1580kv motor with a 20amp 14.8volt maximum power rating, so I have installed a 30amp hobbyking speed controller. I will be running it on a 3 cell (11.1 volt). The results of the current draw and trust measured is shown in the table below:

Prop	Max Current (amps)	Max Thrust (grams)
6×4	10	Did not register
8×4	16.5	220
8x6Orange	23	250
8x6Black	25	320
8×4.5 Triple	27	520
9×5	27	320

Apparently a plane flying through the air will take approximately 10% less current than the same plane static on the ground (due to the air movement over the prop, so I have found on the internet). Based on these numbers, although I think that the 8×6 black and orange trust figures are skewed by the setup, but I would say that the best prop would either be an 8×5 of the black type or the 8×6 orange prop, giving the maximum thrust with closest to the maximum power of the motor, and running it on a 3 cell should give the extra allowance to mean that it will take the current tested without burning out. The triple or the 9×5 prop would give more trust, but are both too far above the motors maximum working load current.