Servo auto bed levelling - Problems

I am trying to get the auto bed levelling working but when i try to find the angle of the servo on pronterface it gives the wrong numbers - m280 s0 gives -53 then without moving the servo would change to 12 then go to -175 and randomly give out numbers also the servo wont move if i give it an angle - out of range - .

servo- sg90 (have tried changing the servo same problem)
ramps 1.4
marlin

You must use P0 with the command: m280 P0 S100
Use positive numbers only.

See this guide:

http://zennmaster.com/random-things/auto-bed-leveling-for-the-makerfarm-prusa-i3-part-3-final-setup

Edited 2 time(s). Last edit at 07/21/2015 06:35PM by imqqmi.

]that is not with setting the angle it it when trying to find out what the angle is.

Screenshot attached

(p4 is the only number that has any details apart from the numbers set in marlin)

I'm not sure if reading the angle is supported, why do you need to? Setting the angle is all that matters, with a bit of trial and error. The servo isn't capable of reporting back the angle as far as I know. If it would work, likely all you'd get is the angle you've given in.

I've looked at the source code, it will give an out of range message if you set S but don't set P which is the servo index, usually servo 0.

If you just do m280 S4 without having configured 5 servos in marlin firmware (servo 0 is the first servo, and I think 3 or 4 is the maximum supported) you read a memory area that's being used by a completely different variable, hence the unpredictable numbers you see. the firmware nor C does any bounds checking. It just checks if the servo index is >= -1.

Anyway, you're not using the command as it was intended. I strongly suggest to use the guide by zennmaster to setup your abl servo.

Got it sorted now thanks for the replies