Hot Servos

[mackrackit]

All three might fail at the same time being they are all driven by the same in-correct code? You have already stated that the code was not good and with out the servos connected to the MCU all was well...

[The Master]

Thats true. The code was originally wrong. It was causing very short pauses of about 6ms. I assume digital servos are fine with really short gaps but could something like that actually break the servos? Or could it just be that the invalid code caused the initial buzzing and the heat caused the rest of the damage?

[Acetronics2]

Hi,

So ... let's resume.

IF those 3 wonderful servos are " so good " ... why not test their behaviour into the skull, with a so simple 555 based servo driver ( 10 components is a maximum ) that will produce neat-known signals ...

here is one of them:
http://www.hvlabs.com/555servo.html

would certainly save time to everyone and, may be money to you ...

Alain

[The Master]

Ok, sounds like a good idea. Ill try and make a 555 circuit tonight. Im pretty confident the signal from my circuit is fine now (it works on the digital servo and the old Sanwa). Im all for saving money though so ill see how the 555 goes.

[The Master]

Unfortunately the 555 has the same results. Again the scope shows quite a good signal. There are very slight variations in the line but they are present even when nothing is connected to the scope. They definately wont cause this problem. Ive zoomed right in and measured the pulses and they are identical width.

I accidentally extended the pause time through my PIC circuit to 30ms and they were twitching even more. I would expect that from analog servos but it seems that if i gradually decrease the pause time they gradually become more stable but 6ms is the shortest i can go to and at that they are back to buzzing and only moving very slightly. Its like the pause time the servos require has become shorter

[falingtrea]

I see that servos have an input voltage range of 4.8VDC to 6VDC. If that power is not clean could it cause the jitter? Are servos ratiometric, so to speak?

[The Master]

The slight variations on my scope are background noise. We are talking like 2mV. Im pretty confident that the supply and signal are both cleaner than my scope is showing and theres no way i could get it any cleaner.

[Acetronics2]

I see that servos have an input voltage range of 4.8VDC to 6VDC. If that power is not clean could it cause the jitter? Are servos ratiometric, so to speak?

Hi, Tim

servos are Theoretically not supply sensitive , actually it is very, very, un noticeable.

This, Halas, is the new proof those hum... servos are to avoid ...

reducing the pause between two pulses only increases the energy given to hold the position ...
what confirms the steady position behaviour is very very bad ... see my #23 post ...

No other solution than select good ones instead of those ...

or try to modify the servo amp gain and dead band ( 10% success ... no more, and 90% risk of oscillating around the position.)

One certitude: amplifier parameters have not been optimised ( often seen for Hitech servos ... )

Alain