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Purchased A 'FlySky' FS-GT2E - Transmitter & Receiver
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 Posted: Wed Nov 29th, 2017 02:33 am
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W C Greene
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Now boys...settle down. There's room for everybody here and feelings shouldn't be an issue.
It doesn't matter how much you spend or what you have, all that matters is if you are happy with what you accomplish.
I don't post much these days, seems that nobody wants to see my tired old lokies with r/c car boards.
But while I ain't posting, I am building and operating and having fun.
When I got into this, r/c car boards were THE ONLY things that were available to do what I wanted.
Some might remember that the reason Freerails has a nice r/c forum is because yours truly badgered the list-owners until they set this up.
Otherwise, there wouldn't be an r/c forum.
Warts and all, this is still the best and the most on the internet.
So, chill out and run a (r/c) train today!

Woodie



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 Posted: Wed Nov 29th, 2017 05:06 am
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Bernd
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That's what I said in #58.
Yes you did. Unfortunately I didn't listen. It was an interesting experiment anyway.
Phil is using a 10amp versus my 30amp. Could that be the difference.  Or is it the frequency of the ESC?
Also need to question whether Phil hooked a motor to his ESC. Lacking a bit of info there.
I'm sure Si will fill the space with useless chatter before we get some semblance of an answer, if we get one at all.
Either way I'm done with that junk equipment.

Bernd



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 Posted: Wed Nov 29th, 2017 02:15 pm
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Helmut
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@Bernd
current rating is not a criterion. There's another aspect which is essential for RR operation - the minimum duty cycle an ESC will offer.
The cheap ones are intended for the car/ boat racing market where you do not need the slow starting speeds a loco does.
Then there's the motor characteristics, such as its own starting voltage.
It is not uncommon for a 6V motor to start at 2V.
The average customer doesn't tolerate a dead band in the beginning, he wants immediate action once the trigger is pulled.
So it is very likely that when you plot R/C channel pulse length vs. duty cycle, you see an offset of the ESC ,
that is a minimum duty cycle >0% ( which would be the ideal theoretical value ).
To test this, one must use a servo tester where you can vary the channel pulse length with a reasonable high resolution.
If you connect the ESC to it, you can determine that minimum duty cycle (= starting voltage ).
Only ESC's with a low offset are really useful for model RR purposes, if you can tolerate the PWM noise.
As Bob laid out, you still may have a jump-start phenomenon that can only be overcome when you use rather low-frequency PWM,
something you don't find in the Chinese ESCs.
This is logical as they aim at a completely different market demand.



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 Posted: Fri Dec 1st, 2017 12:18 am
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Helmut
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Hi all,
after some consideration I finally decided to show how to convert that FlySky 2-channel car TX/RX into something sensible for loco operation.
As you buy cheap, you must be prepared for some tinkering and butchering.
It is not that straightforward a system you can employ as someone here wants to make believe,
at least if you want a decent control sensitivity and range.
You have to replace that noisy cheap car ESC as well if you want something that doesn't torture your ears up to midrange speeds.
Let's concentrate on the TX/RX system first.
I bought mine some years ago, but as the innards are FlySky, I don't think they changed the electronics.
My housing looks differnet, but that's a minor issue.
First, here's what you see once you undo the screws and open it:


Attachment: Conrad9.jpg (Downloaded 116 times)



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 Posted: Fri Dec 1st, 2017 01:25 am
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Bernd
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You have my attention.

Inside  of yours looks close to the one I have.

Bernd

Last edited on Fri Dec 1st, 2017 01:26 am by Bernd



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A REALIST sees a freight train
The LOCOMOTIVE ENGINEER sees three idiots standing on the tracks
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 Posted: Fri Dec 1st, 2017 11:42 am
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Helmut
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The steering knob, which will be used for speed control later, can rotate by 90°.
A steam loco's throttle has the same swing. Direction will be changed by a toggle switch.
So that's pretty close to prototype, and one can live with that.
In another conversion, I just used the electronics ( see my picture in #17 ) in a flat housing where you have that 270° turn.



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 Posted: Fri Dec 1st, 2017 02:51 pm
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Helmut
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Next step is to make the mechanical changes. The "TH" (speed trigger ) pot has to be removed.
The "ST" (steering) pot's centering spring has to go, too. First, you take out the TH pot:





Pull the plug out of its socket and undo the two screws that hold it. It is set aside for later use.
Then there's the ST pot which will become the throttle. Remove the center screw in the wheel and pry it off the pot's axle.
Then remove the three screws in the housing, unplug that, too and pull it out.





That lever and its spring have to be removed.
As soon as you remove the spring the lever will follow and free the pot's movement to some 300°.
We will not be able to use that, however, because its inner workings are such that there is only a useable travel of some 90°.





(Here is an inset I forgot)
The potentiometer will be used to set speed from 0% to 100% for its full 90° swing.
Therefore, its electrical circuit has to be adapted to that prerequisite.
To understand this, one has to see how a channel pulse is used in an ESC.
The channel pulse's 'neutral' duration is 1.5msec.
Full forward is assigned to an 1.8msec, and full reverse to an 0.8msec duration.
The 'ST' pot's respective positions are middle( halfway), full CW, and full CCW.
Its nominal value is 5 kOhms in most cases, so that corresponds to 2.5k, 5k, and 0 ohms.
The input is seeing 2.5, 5, and 0 Volts.
So in this application, the swing from 0% to 100% has to be translated into 2.5V --> 5V,(forward) and 2.5V-->0V (reverse).
The schematic shows how that is done:





I chose these values to arrive at roughly the same resistance value as before,
but it will work when on just replaces the 2k2 resistor with one of the same value as the pot, and omit 3k9.
Anyway, here it shows how it is done.
First you cut the PCB strip leading to the black wire's terminal:





Then you solder the resistors in place (I chose 1% types just to be sure ):





( End of inset)

The pot is to be mounted again, and the knob will get a friction pad, so that it will keep its position easily:





I used a self-adhesive felt pad they sell to protect the floor from chair marks.
More later.



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 Posted: Sat Dec 2nd, 2017 11:01 am
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George Ruthven
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Thks Helmut, you've made my weekend:bow:



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 Posted: Sat Dec 2nd, 2017 06:15 pm
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Bernd
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Helmut,
Excellent step by step.
If I understand the values right of the resistors, they are 2000 ohm and a 3000 ohm or are they 2200 ohm and 3900 ohm?
Bernd 



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A PESSIMIST sees a dark tunnel
An OPTIMIST sees light at the end of the tunnel
A REALIST sees a freight train
The LOCOMOTIVE ENGINEER sees three idiots standing on the tracks
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 Posted: Sun Dec 3rd, 2017 01:32 am
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Helmut
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@Bernd
The resistors are 3900(3k9) & 2200(2k2) Ohms 1%. You can also use just a 5100(5k1) Ohms 1% in place of the 2k2 and leave the 3k9 out.
All this is true only when the pot is 5000 (5k) Ohms! If in doubt, check with a multimeter.



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