Instead of hard coding a specific speed for your race car, here we will use a couple different ways to adjust your speed without having to constantly upload new code.

The first way we are going to adjust the speed is with a simple breadboard trim potentiometer. Pick one up on the Adafruit Shop:

These are our favorite trim pots, perfect for breadboarding and prototyping. They have a long grippy adjustment knob and with 0.1" spacing, they plug into breadboards or...
\$1.25
In Stock

Potentiometers, or Pots for short, are variable resistors that allow us to send different voltages to the Feather analog pin. Wiring it up is super simple. Just connect one of the outside pins to a 3.3V pin, and the other outside pin to ground. Then, connect the middle pin to the A0 pin on the Feather. For a reminder on which pin is which on the Bluefruit Feather, click here.

The code to get this all working is incredibly simple. Just copy and paste in the code below to the top of your main loop.

```//Set your motor speed

So, it should look something like this now:

```void loop(void)
{

}```

What we are doing here is reading that analog pin, and the Feather is going to pull a number from 0 to 1023, depending on which direction the arrow is facing on your pot. Because the motor controller needs a value from 0 to 255, we are using the map() function.

Go ahead and upload this code to your race car, and turn the pot, then press forward on the controller to see how it works. Keep changing to direction of the arrow on the pot to adjust the speed.

## Using the Controller to Control Speed

If you would rather just control your car's speed using the extra 4 buttons on the controller, it is also pretty easy to set up. First off, we need to set up a global speed variable. Anywhere above the sketch setup, add in something like this:

`int robotSpeed = 100;`

In the main loop, we can then use that variable to set the motor speed using:

```L_MOTOR->setSpeed(robotSpeed);
R_MOTOR->setSpeed(robotSpeed);```

Then, all we need to do is increment the speed up every time we press the 1 button, and down every time we press the 3 button.

```if(buttnum == 1){
if(robotSpeed <= 245){
robotSpeed = robotSpeed + 10;
}
}

if(buttnum == 2){
}

if(buttnum == 3){
if(robotSpeed >=10){
robotSpeed = robotSpeed - 10;
}
}

if(buttnum == 4){
}```

Here is the whole block of code for you to copy and paste in:

```/*********************************************************************
This is an example for our nRF51822 based Bluefruit LE modules

Modified to drive a 3-wheeled BLE Robot Rover! by http://james.devi.to

Pick one up today in the Adafruit shop!

Adafruit invests time and resources providing this open source code,

All text above, and the splash screen below must be included in
any redistribution
*********************************************************************/

#include <string.h>
#include <Arduino.h>
#include <SPI.h>
#if not defined (_VARIANT_ARDUINO_DUE_X_)
#include <SoftwareSerial.h>
#endif

#include "BluefruitConfig.h"

#include <Wire.h>

// Create the motor shield object with the default I2C address

// And connect 2 DC motors to port M3 & M4 !

// A small helper
void error(const __FlashStringHelper*err) {
Serial.println(err);
while (1);
}

// function prototypes over in packetparser.cpp
float parsefloat(uint8_t *buffer);
void printHex(const uint8_t * data, const uint32_t numBytes);

// the packet buffer
extern uint8_t packetbuffer[];

char buf[60];

int robotSpeed = 100;

/**************************************************************************/
/*!
@brief  Sets up the HW an the BLE module (this function is called
automatically on startup)
*/
/**************************************************************************/
void setup(void)
{
Serial.begin(9600);

AFMS.begin();  // create with the default frequency 1.6KHz

// turn on motors
L_MOTOR->setSpeed(0);
L_MOTOR->run(RELEASE);

R_MOTOR->setSpeed(0);
R_MOTOR->run(RELEASE);

Serial.begin(115200);
Serial.println(F("-----------------------------------------"));

/* Initialize the module */
BLEsetup();

//Set your motor speed (255 Max)
L_MOTOR->setSpeed(robotSpeed);
R_MOTOR->setSpeed(robotSpeed);
}

void loop(void)
{
L_MOTOR->setSpeed(robotSpeed);
R_MOTOR->setSpeed(robotSpeed);

}

// Buttons
if (packetbuffer[1] == 'B') {

uint8_t buttnum = packetbuffer[2] - '0';
boolean pressed = packetbuffer[3] - '0';

if (pressed) {
if(buttnum == 1){
if(robotSpeed <= 245){
robotSpeed = robotSpeed + 10;
}

}

if(buttnum == 2){

}

if(buttnum == 3){
if(robotSpeed >=10){
robotSpeed = robotSpeed - 10;
}
}

if(buttnum == 4){

}

if(buttnum == 5){
L_MOTOR->run(FORWARD);
R_MOTOR->run(FORWARD);
}

if(buttnum == 6){
L_MOTOR->run(BACKWARD);
R_MOTOR->run(BACKWARD);
}

if(buttnum == 7){
L_MOTOR->run(RELEASE);
R_MOTOR->run(FORWARD);
}

if(buttnum == 8){
L_MOTOR->run(FORWARD);
R_MOTOR->run(RELEASE);
}
}
else {
L_MOTOR->run(RELEASE);
R_MOTOR->run(RELEASE);
}
}
}

void BLEsetup(){
Serial.print(F("Initialising the Bluefruit LE module: "));

if ( !ble.begin(VERBOSE_MODE) )
{
error(F("Couldn't find Bluefruit, make sure it's in CoMmanD mode & check wiring?"));
}
Serial.println( F("OK!") );

/* Perform a factory reset to make sure everything is in a known state */
Serial.println(F("Performing a factory reset: "));
if (! ble.factoryReset() ){
error(F("Couldn't factory reset"));
}

//Convert the name change command to a char array

//Change the broadcast device name here!
if(ble.sendCommandCheckOK(buf)){
Serial.println("name changed");
}
delay(250);

//reset to take effect
if(ble.sendCommandCheckOK("ATZ")){
Serial.println("resetting");
}
delay(250);

//Confirm name change
ble.sendCommandCheckOK("AT+GAPDEVNAME");

/* Disable command echo from Bluefruit */
ble.echo(false);

Serial.println("Requesting Bluefruit info:");
/* Print Bluefruit information */
ble.info();

Serial.println(F("Then activate/use the sensors, color picker, game controller, etc!"));
Serial.println();

ble.verbose(false);  // debug info is a little annoying after this point!

/* Wait for connection */
while (! ble.isConnected()) {
delay(500);
}

Serial.println(F("*****************"));

// Set Bluefruit to DATA mode
Serial.println( F("Switching to DATA mode!") );
ble.setMode(BLUEFRUIT_MODE_DATA);

Serial.println(F("*****************"));
}

```

This guide was first published on Jun 01, 2017. It was last updated on Jun 01, 2017.