user3638: I have found bunch of information about how to hack an RC car with a PCB; and how to control an Arduino from a receiver. Also how to run a servo from an Arduino, but I'm looking for a way to make an Arduino send signals to a 27 MHz 3 channel receiver, Using three potentiometers to decide servo location.
Is there any information about this somewhere? - I have an old transmitter lying around if needed.
Links, pointers - anything is welcome.
[It does not have to be 27 MHz AM, it is just what I have on the shelve, without investing in new gear]

user3913: Many RC TX have a remote connector where you can input the signal and not having to open them.
In any case, 27 MHz RC are a train of pulses, of variable width, from 2 to 20 ms each, one for each channel, flowed by a 20 ms pause.
This can be recreated in a single output pin.

user49887: Consider the methods of US patent 9,996,079 (linked URL):
"Radio frequency device detection and intervention": US 20180081354 A1
After reverse engineering the badly written descriptive, you should be able to come up with an Arduino board set.
P.S. Try not to copy the whole patent.

user643: The easiest way would be to open up the transmitter, desolder the potentiometer used for the stick and solder the cables to Arduino's PWM instead. Then use analogWrite() to simulate stick position. If your TX would use that potentiometer with more than 5 V, you'll not able to use full ppm values. A RC or a RCL filter may be needed between PWM output and RC input to "smooth" the PWM into an analog signal. There are a lot of online calculator to find good R, C and L to polish your signal.
This assuming your TX is using potentiometer like stick; if it is a really cheap one, it may be using buttons. If this is the case, then you connect a transistor in parallel with the button, that way you can keep manual button.
Another way is to program your Arduino to look for ppm signal (normally 50 Hz with high starting value with a period from 500 to 2000 µs) and then look for this signal into the Tx PCB; if found cut the trace of the generator and solder your cable from Arduino. I've seen around a lot of libraries outputting ppm (they are used on drones to mix single ppm channel back to PPM to use only one pin from logic board without having to hack standard RX

3638: <p>I have found bunch of information about how to hack an RC car with a PCB; and how to control an Arduino from a receiver. Also how to run a servo from an Arduino, but I'm looking for a way to make an Arduino send signals to a 27&nbsp;MHz 3 channel receiver, Using three potentiometers to decide servo location.</p>

<p>Is there any information about this somewhere? - I have an old transmitter lying around if needed.</p>

<p>Links, pointers - anything is welcome.</p>

<p>[It does not have to be 27&nbsp;MHz AM, it is just what I have on the shelve, without investing in new gear]</p>
 3913: <p>Many RC TX have a remote connector where you can input the signal and not having to open them.</p>

<p>In any case, 27&nbsp;MHz RC are a train of pulses, of variable width, from 2 to 20&nbsp;ms each, one for each channel, flowed by a 20&nbsp;ms pause.</p>

<p>This can be recreated in a single output pin.</p>
 49887: <p>Consider the methods of US patent 9,996,079 (linked URL):</p>

<p>"Radio frequency device detection and intervention": <a href="http://patents.com/us-9996079.html" rel="nofollow noreferrer">US 20180081354 A1</a></p>

<p>After reverse engineering the badly written descriptive, you should be able to come up with an Arduino board set.</p>

<p>P.S. Try not to copy the whole patent.</p>
 643: <p>The easiest way would be to open up the transmitter, desolder the potentiometer used for the stick and solder the cables to Arduino's PWM instead. Then use <code>analogWrite()</code> to simulate stick position. If your TX would use that potentiometer with more than 5&nbsp;V, you'll not able to use full ppm values. A RC or a RCL filter may be needed between PWM output and RC input to "smooth" the PWM into an analog signal. There are a lot of online calculator to find good <em>R, C and L</em> to polish your signal.</p>

<p>This assuming your TX is using potentiometer like stick; if it is a really cheap one, it may be using <em>buttons</em>. If this is the case, then you connect a transistor in parallel with the button, that way you can keep manual button.</p>

<p>Another way is to program your Arduino to look for ppm signal (normally 50&nbsp;Hz with high starting value with a period from 500 to 2000&nbsp;µs) and then look for this signal into the Tx PCB; if found cut the trace of the generator and solder your cable from Arduino. I've seen around a lot of libraries outputting ppm (they are used on drones to mix single ppm channel back to PPM to use only one pin from logic board without having to hack standard RX</p>
