Different motors speed?

Using Arduino Motors, Mechanics, Power and CNC
1

So i have 2 motors connected to a ESC each and both ESC's are connected to battery, GND on the arduino board and two different pins (8 and 9).

Servo M1;
Servo M2;

I initiate them with :

M1.attach(8);
M1.write(40);
M2.attach(9);
M2.write(40);

After that i can change the speed using the command
M1.writeMicroseconds(value);

But the problem is, each motor accepts different values. Like if I set both of them on 1300, they will have different speeds.
M1's minimum value is 1160 , M2's minimum is 1080.
So why is this difference and how to fix this?

2

Are the Motors identical? Does one have a different stepping Ratio than the other?

3

ESC's can be calibrated. Look at the instructions for the ESC to find out how. For example, ESC's running the SimonK firmware use this process:

8. How to do throttle calibration
Disconnect the battery. Push your radio throttle to maximum, 
connect the battery, wait for the 3 beeps (di da di), wait for 1s, you 
will hear a short beep (di). Then immediately lower the throttle to minimum. 
You will then hear another unique 2 beeps (di di), indicating you are setting
 the low value. If you hear a long beep, it means the low throttle set. 
Disconnect the battery, throttle calibration is done. If you hear a short beep, 
it means low throttle set failed. You need to do the calibration again.
4

JaBa:
Are the Motors identical? Does one have a different stepping Ratio than the other?

They are identical.

5

You probably need a set of variables for each motor which you can adjust to get values that give the same RPM. I certainly would not expect the same number to give the exact same RPM. There will be some variations in the ESCs and more variation in the motors.

...R

6

Many people re-flash ESCs to get predictable and fast response for use with quadcopters - worth
investigating.