Over-engineering and excessive technology

[Elliot]

Hi There,

Are there any FPV(first person view) RC pilots on this forum? I am taking my first flight this weekend weather permitting in the Hangar 9 spitfire (electric) and would like a few tips if anyone has any experience in this area.. (Pictures in my gallery).

Thanks

[David Ashby - Moderator]

Very interesting pictures Elliott, can you tell us a little more about the set-up?

David.

[Elliot]

I am using a PIC microcontroller (PIC18F4520)(£1.80) on the main PCB in the plane, this reads a temperature sensor(£0.80) just to the rear left of the canopy, a 15psi pressure sensor(£14) on the PCB for altitude, a 30 psi pressure sensor(£15) (pipe feed) on the PCB for speed(venturi), also battery voltage and signal strength for the 433MHz receiver(£10) as analog inputs and displaying them on the GLCD.

It also looks at 2 inputs from micro switches mounted at the retracts when they are down, this is displayed on the graphical LCD(£8) inside the cockpit. I am feeding the flap servo via my PCB and reading the PWM from the receiver and displaying the flap position on the GLCD also.

The colour camera (£75) video feed is sent via a 2.4GHz transmitter (£34) on the underside of the PCB, this is received by a 2.4GHz TV receiver (£80)with video output for the i-goggles (£110) which uses two gyros(£30 each) for pitch and yaw. This data is sent via a 433Mhz transmitter (£14) to the receiver on the plane, the data is read by the PIC and sends servo commands to the camera pitch and yaw servos...

Pretty simple hey!

The range of the system is 1km but I am yet to test the range, everything seems to be working well although I am leaving it running on the bench for a couple of days just to be sure.

I am currently working on a cut down version which displays the information in the screen using an OSD chip like your video player or TV has, it will also use micro servos.. The aim is to put it in the Ripmax spitfire and make it more accessible to the majority.

I won't be producing it in any way as it is purely for pleasure but will be happy to have a number of PCB's made if I get at least 5 people who want to make one for themselves.. I will give them the parts list and HEX code for the chips and they can put one together.

You'll need a fine tip soldering Iron and an melabs usb pic programmer to program the PICs.

I might be persuaded at some point to produce a couple populated PCB's at cost, camera, servos and i-goggles will still need to be acquired though, I am quite busy at the moment and I have a baby girl due in December so maybe after Christmas if I get enough nutters wanting to do this as well.

I am very interested in anyone in my area who fly's quite regularly so please let me know if you do.. Electric only though Heli or plane.

[David Ashby - Moderator]

Very impressive, please let us know how it goes

[Bladerunner]

Interesting...You may get a couple of takers if you release the source, esp in C (Hitech, CCS, IAR).

Have fun. 

[Lee Morgan]

OMG I like to edit vids and I fly around with my flycamone straped to the belly pan but I am gob smacked by the tech that you using, If your able to, a few pics of the system up and running would be great, maybe even a vid or two.

Watching this thread in aww

Lee

[Elliot]

Weather permitting I am aiming for a maiden flight this weekend, all will be video'd...

[Elliot]

Unfortunately I had some serious vibration issues just as she took to the air and ended up stalling and kart wheeling on the strip, I bent one of the undercarriage slightly and the tail wheel.

I aim to correct this and get her in the air this comming saturday, I have a video of the flight which I am currently uploading to youtube.. I will post a link shortly.

[Elliot]

Not the video I had hoped to post but once I have resolved the vibration issue this week hopefully I should have something good to post next sunday..

http://www.youtube.com/watch?v=noMFudwK4TQ

You can hear the noise just as I fully open her up, lucky none of the good stuff got damaged.

[Former Member]

[This posting has been removed]

[Elliot]

You may be right about the tip stall although this plane had enough power to pull vertical, I had it doing so on Friday at full rpm..I had noticed that the nerl on the spinner back plate was radial and on the prop adaptor it was all in one direction, this lead to a varying offset angle of the spinner which varied at different rotational radii.

I set the position to an almost nil wobble with the tip of the spinner creating a circle less than 0.5mm in diameter and testing the day before showed that it was fine, I beleive that it must have been on the edge of it happening at a point of resonance with perhaps the difference in temperature of almost 20 degrees C and due to the chassis mount for the Hacker being quite a distance from the main fusilage and the vibrations through the plane from the uneven ground on take off allowed the oscilation to become exaggerated once a certain rmp was reached, as a result a large amount of power and thrust was lost causing the plane to stall.

My Hacker A50 16S is 380 kv (rpm per volt) and as I am runing 6 cells that makes 25.2v maximum.

This is an rpm of 9576.....

 My Prop is 15 inches from tip to tip and with an air temperature of 10 DegC I calculate that my prop tip speed is 427.3mph or Mach 0.5! half the speed required for the tips to reach super sonic.

[Tim Mackey]

Insufficient airspeed at take off is my .02 worth. Glad the damage was minot though - you have done some excellent work there Elliot

[Elliot]

I have just found that all four allen key bolts have come loose from the vibration of that one attempt, all tightened up and ready for a test once the threadlock goes off....

I'll try without the spinner then with to see it it is cusing the problem.... there is a slight wobble which is only really visible on the outer edge of the aluminium spinner back plate, I am hoping its not the motor shaft. Same amount as pre flight so I know it's not crash damage. 

Does anyone have a good suggestion for 3 bladed with Hacker A50 16L and a H9 Spit? I would like to go down this avenue when my spinner arrive next month and want to make sure I am optimum.

[Tim Mackey]

Well this motor is suited for a fairly wide range of 2 bladers with an 5 cell LiPo @ approx 18.5V nominal and you are using  6 cells @ 22V nominal.  I doubt very much that you are holding 25.2V under load, ......more likely  around 21 -22V, depending on the quality of the packs, and of course the load which is the sze of prop. Furthermore, although the K/V is 378, that too will drop a bit under load, so I would expect static of around 7800- 8000 realistically.

Have you done an RPM measurement?

The motor is rated at 40A on 5s so that equals around 720 watts, lets call it a 750 watt motor, with short bursts of up to 850 - 900 watts. I dont know the AUW of your model, but the kit as standard states 8.5 -9.5lbs and thats before you add in all the extras that you have fitted. You are using 6s on a 15" X ?? prop, and the recommended range is 14 X 7 - 16 X 12 ( on 5s ) which obviously will be at the top end of the current limits. If I may assume for a moment that she has come out around midway of 9lbs, you may actually be a little marginal on that setup. Do you have a wattmeter, and if so, what Amps are you pulling static? Once you have established this, the usual rule of thumb to move to a 3 blader is to drop an inch in diameter and as the maximum recommended for a 5s pack was a 2 blade 16 X 12,  allowing for the fact you are on 6s not 5s I should think you could probably go to 16 X 8, therefore in 3 blader terms how about 15 X 8? -rememberng of course not to exceed the 750-800 Watt limit of the motor.

[Elliot]

Thanks, I am not sure exactly what current I am pulling.. I will order a shunt resistor tomorrow to find out although at the moment I am getting to about 60% throttle and everything is shaking to bits... the motor mount has fractured and I have puth the prop adaptor in the lathe to see if it is at fault... And it seems to be.. I will order a new one of these when I get home shortly and try again to spin her up.... I'm itching to get this bird airbourne!

[Tim Mackey]

I would have thought a keen electric flyer such as yourself would get a proper wattmeter, using a shunt is a bit inflexible and not altogether accurate.

[Elliot]

I've not really needed one up to now, I did a project for greenpower racer electric cars for schools which involved building a speed controller which had to measure the current, I used a 70A shunt resitor which seemed to be very accurate although a bit on the heavy side...

Do you have a link to where I can get one? 

[Tim Mackey]

Amongst many others, Brian Collins have them

HERE

[Elliot]

I expect it has a microcontroller reading the voltage across the wires and across a shunt resitor inside and displaying the readings on the GLCD, I was going to include a current measurement as part of the system but the shunt I was looking at was too heavy.

[Bladerunner]

He! He! You gotta love electrickery. Good luck and have fun.

[Steve Hargreaves - Moderator]

Like Timbo I think you might be a bit marginal on power here. If we use the 100 watt per pound rule you would need around 900 watts for reasonable performance....from Timbos calculations you only seem to have 750 watts so a bit of a shorttfall. Looking at the video clip it does look as though the aircraft lifted off too soon.....more speed needed methinks!!!!!!

Incidentally if you don't know what current you're pulling might it be way in excess of the 40A max of the motor? Might you have blown a coil or two which could account for the rough running & vibration....take the prop, spinner & adaptor off & run the motor...all smooth? Add one part at a time until you find the culprit......

Some good stuff with the electronics though...I even understood some of it!!!!! Can't wait to see the results!!!

[David Ashby - Moderator]

Hmm, I'm worried about those flaps. I never bother with flaps for take off with my H9 Spit' and if they're working unevenly could they have contributed to that sudden jump and stall?

[Elliot]

I have just founf the problem after some serious head scratching, the A50 shaft was very slightly bent causing a wobble... I've had it in the vice and with the 15x8 3 bladed suggested it is running nicely... Possibly to much flap on take off may be the case and not enough speed.... More or less ready for saturday now though...

[Elliot]

Not sure if anyone is interested but I am loging progress of this project on a web page..

http://www.harrison-croft.com/Hangar9Spitfire/Hangar9Spitfire.htm

It's easier and quicker to put up images and video clips..

That spinner and prop looks very sexy!

[Former Member]

[This posting has been removed]