I don’t think if the servo
I don’t think if the servo is off it spins 360 degrees. Otherwise this servo could not be used for air planes etc. Imagine the servo starting to rotate if you lose contact with the model.
Saw these servos: https://www.robotshop.com/world/specialty-servo-en.html
They have position, temperature, load, input voltage feedback, but the price…
You need to clarify "off"
Unpowered or powered without a control signal? I have seen some servos that react differently to the latter condition (stay where they are, center or twitch) and my analog servos offer little resistance to being moved when unpowered. When they are still on a plane, I believe they are powered and receiving a steady control value.
Here is a quote from the
Here is a quote from the reviews:
I bought this servo and just received it. Compared to other 0.08s servo nothing much different. but for price this servo wins a lot. Quite fast and the rotation can do 360 degree when it off. The only bad points is this servo does not come with heat sink. after 10min of use this servo become hot. But overall, Great servo for money.
I believe “off” means unpowered (or unplugged) and rotated by hand. As we all know from Anton’s magnetic servo sensor (https://www.robotshop.com/letsmakerobots/node/18615) it has no stop, so perhaps the manufacturers did not include a hard stop for the gears (usually used to protect the potentiometer from breaking). Also, if one looks at the “exploded” picture from the HobbyKing site, the PCB of the servo looks different than for a regular servo. So I was thinking "what if…"
A regular servo has a built in oscilator, who’s period is adjusted by the potentiometer. This period is fed to a comparator that compares it to the control signal. The difference is fed to the motor so it spins one way or the other until the signals match. Now think about this for a little. If the range of the built in generator is fixed (say from 1ms up to 2ms), feeding an out of range signal would make the motor spin continuously, as there will always be a difference. It’s as simple as that. So theoretically, it should work, but it all depends how the board was designed.
Cheers!
Edit: While going to work I was still thinking about this and figured that as the servo horn rotates over 360 degrees, the sensor will adjust the internal oscilator period and I figured the motor will start to turn the other way, but I was wrong. A greater control singnal period will never be matched by the internal oscilator, so the motor will still be spinning. But the speed might be affected if the motor’s speed is proportional with the difference between the 2 signals.
So here are the things that need to be addressed:
- clamping of the internal oscilator period so it works only in the 1ms-2ms range;
- adding an extra comparator(s) that looks at the period of the control signal and if it is in the 1-2 ms range it compares it further with the internal oscilator period, or it compares it further with a fixed value, say 1.5 ms period and feeds the difference as a proportional speed to the motor.
The last part is still blurry in my mind on how can be implemented with comparators, a microcontroller can simplify things a lot, but it will result in something similar with Anton’s method. I’ll keep on thinking, perhaps some of you guys can chip in some ideas…
