Large Model Association Forum

I have added reverse polarity protection, not to servos connected but only to the unit it's self.
The unit will use standard 3 pin RC connectors so this is unlikely to happen, but at a cost of 3p per unit I thought it worth including
Should the flight battery have the plug on it the wrong way around the unit will not connect
The battery connector will be spaced away from the others to identify it

I have also added the recommend filtering for use in a noisy environment ( that means radio frequency and spark stuff ).

I have to say the Jeti system looks amazing but it would cost me a couple of thousand quid + to change all my stuff!
Think I will stick with Futaba and Steve's solution as I am just about to retire and will have to tighten my belt a bit.
Glen, I will try and take some pictures of my very crude cowl flap mechanics.

I put the circuit together on a breadboard today with an Arduino nano, connected everything and started testing, it almost worked as advertised except for the override switches (a coding error), and the face palm after an hour of trying to get the servo to move due to not having the power to it turned on lol
The Arduino cannot supply enough power to run a full size servo, hence the separate power to it on the breadboard, not an issue with the finished unit that will not be powered from the supply built into an Arduino

Youtube just gave me this video that may be helpful https://www.youtube.com/watch?v=8OmJISrSo-Q

All functions are now working
Adding the LCD display made it run dog slow with the servo ticking 1 degree per second, operating an override switch gave an instant full open but requiring a full minute to return to the prior position so I will not include an optional temperature display in the current form.

The issue that I am dealing with at the moment is hysteresis, if I hold the sensor to warm it up then the servo goes to fully open because the set temperature is lower than the 1 degree warmer sensor in my hand.
The next step is to use a hair dryer and vary the distance, adjusting the code so that the amount of additional opening depends on the difference between the set and actual temperature, some nasty maths may be required for this

Once it is working correctly with the Arduino nano I will put together the full circuit on the breadboard with the actual chip that will be used as a final test before ordering circuit boards.

To recap on what is working and tested ----

All adjustments are by screwdriver.
Upper and lower servo travel limits adjustable by 10 degrees.
Minimum servo travel 90 degrees.
Maximum servo travel 110 degrees.
Servo reverse option by pulling out a jumper ( like a bind plug, in or out ).
Broken sensor causes max open.
Temperature adjustable

The finished unit will draw naff all from the flight battery

Glen, here are some photos of the cowl flaps on the p40.
They are double skinned with a spacer and a Mylar connector. A servo is up front in the cowl with one arm split in two connected to control horns.
The Corsair has the same principle but a central servo on it’s side and six arms that push the flaps out.
Hope that helps.

Today's added feature is some spark suppression on the wires to the temperature sensor that will be in a very sparky area, something with the complicated sounding name of a "Common Mode Choke".
What it actual does is if a spark puts a spike on both wires like ____|____ then it turns one upside down and subtracts it from the other wire, 1 added to -1 = 0

I hope these occasional updates are actually of interest to more that one reader

I hope these occasional updates are actually of interest to more that one reader
Very interesting, the LMA resident nutty professor!

The new code works on how any degrees above the set temperature to control the amount of opening of the flaps, the sensor that I am working with has a max rating of 125C.
I may need to change to a higher rated sensor but at 200C solder begins to melt
The current sensor costs £1 for 5, the higher temperature one costs £10 for 10
The way that I am connecting the sensor at the moment is by taking the pins out of a servo cable a chopping the pins off, this gives a short section that the sensor wires can be inserted into and then soldered so that it is user replaceable

The main cost of the circuit boards as previously mentioned is the postage, the interesting part is that I am using surface mount where possible ( no wires on them to poke through holes to solder ).
There are 2 ways that I can build these, either order a stencil with the circuit boards at £5 , or to use the free assembly service that JLCPCB are currently offering.
Here is what is involved with using a stencil skip to 2:50 https://www.youtube.com/watch?v=uXvXwzQf1gU
The free assembly service is not exactly free, here is a video of what happens https://www.youtube.com/watch?v=pHNpayYhBvM

Standard components are already loaded on the machine, some components are from the Extended range that may not even be in a magazine ready to fit into the machine, there is a £1.50 charge for loading the machine with them ( the common mode choke for example is from the Extended range ). If there are 10 Extended range components on the pcb then that is an extra £15

Either way I still have to solder the through hole components, this gives the option of supplying a semi kit where the through hole parts are supplied but need fitting and soldering, initial units will be fully assembled

I am trying to keep this interesting and not bafflingly technical

There is also a customs charge (inc the postage) when it enters the country if above a certain level Fortunately I can get around this

I will try and upload some pictures and videos

Work on this is on hold for a few days due to having to urgently relocate some plumbing and electrical stuff in the house
Normal service should resume at the weekend once finished:)

Hope the plumbing and electrics go according to plan.

It's not quite going to plan on the plumbing side due to the required part is not available

Getting back to the topic, it will be easier if if the opening depends on how much above the set temperature that the sensor is:)
Working on about 100 degrees of servo travel then I can scale 50 degrees above the set temperature to give a 2 degree per degree C opening above the sensor temperature to give full opening at plus 50 C.
What I actually want is something starting at 1C per 1 Degree and ending at 5 per C at 50 over.

I am thinking of that movie where they are going to overheat on the ground and request to either get airborne or shut down

I had a play with the code tonight and will test it Friday, my furlough is ending so I have less time to spend on this. If the code works correctly then the next step is to build the same circuit on a 2nd breadboard using the actual chip and components that will be used in the finished project. This involves several small adaptor pcb's to plug in surface mount stuff.

[url][/url]PCB's ordered via 1st class mail, the extra 10 quid for DHL would get a customs charge on them, yes folks HM Revenue & Customs include the shipping cost, buy something for a fiver and pay express shipping and it may put you over the limit
The limits are £15 inc shipping unless sent as a gift, for "gifts" it is £39
HM Revenue & Customs only seem to look at stuff near the 39 quid inc shipping and bung on at least a tenner

For a full blown rant about HM GusThumbs & Neck Size I suggest Big Cive's -
https://youtu.be/rl59UN26gFM?t=10766

So a bit of old school engineering for cowl flaps, no electronics, no servos, just some wire or to be more accurate heat sensitive coils as per old carburetor choke control.

Why not use a coil mounted fairly close to the old cylinder head, with a bit of planning a few simple coils could easily open and close the cowl flaps without all those electronics.

I am fairly sure that quite a few systems relied on a bit of heat, I mean old yank tanks even loved the vacuum system to drive wipers and all sorts of other systems. I have used nicely wound coils to open cooling flaps on a purpose built heating system in my father's growing tunnels.

Just a different course to achieve the same result.

Interesting Alan, never thought of that.
Thanks for the update Steve.

The PCB's arrived last week, I now have to find the time to take some photos of the breadbord lash up, unboxing the PCB's, solder them and of the assembled board
Slight change to the amount of servo travel, it was from 90 degrees adjustable up to 120, it will now be 90 degrees +/- 5 at each end of the stroke ( 45 to 95 degrees total travel), which will make it compatible to use an ESC so that it can also be used to run a cooling fan

Here is the breadboard lash up
Bottom left the battery box, the white wire above it is servo power that bypasses the regulator board on the left.
The 3 blue things are the adjusters for temperature and servo travel end points.
Right hand size is an Ardino Nano and bellow it the 2 line display that I am using to debug things.
Top right are 2 override switches that cause full open.
Just to the right of the right blue adjuster is the jumper to select servo reverse by removing it.
And finally hiding behind the servo is the actual sensor that decided to be photo shy



The unboxing, 4 packs of PCB's and the stencil, I am showing the box for the JLCPCB logo because the do such a good service, although they forgot to put the free gift in this time.



A closer look at the order, 4packs of 5 100mm x 100mm boards containing multiple actual PCB's, they cost $2 for the first pack and $3 each for the other 3. The PCB's are top left mounts for the 200C sensor if needed, bottom left mounts for the 100C sensor, top right mounts for the temperature adjuster, bottom right the actual PCB's for the controller.
Everything is sat on the laser cut stainless steel solder paste stencil (about a fiver).

Great stuff Steve, getting very excited now. Let me know when you would like some dosh.

If you are wondering what the stencil is for then this video shows and explains things
https://www.youtube.com/watch?v=qyDRHI4YeMI