Signal noise on R/C car channel output

Doing a little project for work and trying to get the Arduino hooked to an RC car to read the throttle channel output and send that via bluetooth to a nearby laptop which will output an animation based on that speed.

Initial test worked very well and signals from my airplane Tx were solid with very little variance. Once the proof of concept worked, we went ahead and purchased a Traxxas car. I have a wire going from pin 5 to the signal wire on the Rx. With the serial monitor up and arduino powered via my usb cable, the #s jump from the 1400 (where its supposed to be) to 6000 and sometimes 11000. Even more interesting, is when I engaged the throttle via the transmitter, values went down to 30-50...?? I removed the Rx from the car and powered it via the 5v on arduino...#s are solid.

So, it appears the battery or esc is giving a lot of interference. Do I need to use a different kind of wire? Or ground it somehow?

int ch1; // Here's where we'll keep our channel values
int ledPin = 11;

void setup() {
  pinMode(5, INPUT); 
  pinMode(ledPin, OUTPUT);

  Serial.begin(9600);
}

void loop() {
  ch1 = pulseIn(5, HIGH, 25000); // Read the pulse width of the channel
  
  //Serial.print("Channel 1:"); // Print the value of 
  Serial.println(ch1);        // each channel
  
  ch1 = constrain(ch1, 1120, 1900);
  int brightness = map(ch1, 1120, 1900, 0, 255);
  analogWrite(ledPin, brightness);

  delay(250);
}

ESCs put out huges amounts of interference, they are switching 10's of amps.

Keep signals well away from high current paths, use shielded cables, definitely
check the ground layout isn't feeding IR noise directly into your Arduino / RX.

I figured as much. I also found it interesting that I was getting random readings just touching the wire when it wasn't plugged into the Rx. I tried moving it as far away from the other components as my arduino starter-box wires would allow me, but made no difference.

What kind of shielded wires would you suggest? With those, would I still only need to plug it directly from my Rx to the arduino?

Touching the wire is putting your voltage on it, which will be typically 50V or so
inside a building with mains electricity. The current available is tiny so that doesn't
hurt you or the Arduino.

Shielded cable with a shield? Go for cheap and flexible if you can, shield to ground.

I found some shielded microphone wire at the store. Wired that up and the issue disappeared. Thanks all.

Good - its not always that simple, but luckily it was for you!