How do you reverse a servo?

Hi guys,
Can anyone tell me how to (electronically) reverse the operation of a servo?
I need to do it this way as opposed to using the Tx, for a scale project and as the servo will be irritrievably burried by the end of the week, I need the answer quick!
Please keep the reply simple and tell it like you are telling a complete idiot!
I know there is someone out there with the answer!
Cheers and merry Christmas to all,
Rob.

[gambit]

The yellow (or white) wire going to the servo is the signal wire. The signal is a pulse of +5v, whose length determines the position of the servo. A 1ms pulse is the minimum pulse length and indicates the lowest position of the servo. A 2ms pulse is the maximum pulse length and represents the highest servo position. So a pulse that is 1.5ms will put the servo in the center position.

To reverse the servo, you need an electronic servo reversing circuit that basically changes the length of the pulse. I'm sure you can find one on the internet. Look here:
http://www.welwyn.demon.co.uk/by_me.htm



[This message has been edited by gambit (edited 12-18-2001).]

[JJ]

If you need to make a servo which goes the other way in itself, two things need changing inside it.
The motor connections need swapping.
The feedback pot (should be at the bottom of the output shaft) needs its outer two wires swapping. The pot will have three wires, the centre one stays put.
Warning - at micro servo sizes these mods are tricky and need good soldering skills, and will of course invalidate any warranty!
If you aren't sure, finding a "servo reverser" circuit to fit between the receiver and servo sounds a better idea.
They are commercially available, the SMS one would need to be de-cased http://smservicesuk.co.uk/acatalog/sm29rev.html for weight for a microheli, or ring and ask if they will do a shrink-wrap version for you.

Or you could reverse the transmitter !

Martyn, TX is an alternative way of writting transmitter. Hope this helps

[This message has been edited by anks (edited 12-18-2001).]

Thanks guys,
I reversed the servo tonight and it works just fine.
Gambit, although I chose JJ's solution, your reply is more than helpful.
The scale model is not (for a change) a Heli', but a large(ish) DH Mosquito, and I want to slow the U/C. http://www.welwyn.demon.co.uk/by_me.htm
have the answer!
Thanks again, it just goes to show what this BB is best at!
Cheers and merry Christmas all,
Rob.