Hi,
I was wondering if anyone had any experience with these servos? I just purchased one and it can rotate a couple of full revolutions but I stopped after 5 or 6 rotations because I was afraid it would break.
What happens if you issue a pulse longer than the recommended for a servo? Would it damage it? How can I determine the pulse width boundaries for a servo such as this?
Thanks,
Stephen
unless its continus rotation
then it will break the gears,pot(s),or the electronics
The HS-785 is a sail-winch servo, made to turn multiple revolutions, as opposed to a maximum of half a turn.
…but then, you already knew that.
In order to achieve the multiple-turn aspect, they had to eliminate the physical stops from the design, and use a multi-turn pot for position feedback. Either that, or they’re using a traditional pot on a separate gearing system, while the output rotates several times over the span of a standard signal width.
One way or the other, there likely won’t be any physical stops on the output to prevent you from overrunning the ends of travel, so I suspect that you would want to take it easy with the hand-spinning of the output shaft. Similarly, the lack of stops might make it possible to physically damage the servo by sending it an out-of-range pulse which could cause it to over- or under-run the pot. Then again, they may have thought of that already, including some sort of clutch or coupler to prevent damage, or a physical stop that works on the multiple turns that the output can produce. Still, much like micro servos, which are often quite able to strip out their own gears by commanding an out-of-range position, I’d suggest you take a bit of extra care when working with your sail-winch servo, just to be on the safe side. Maybe testing the code to send the positioning pulses with a standard servo in its place would be prudent; that way, you’ll know that you won’t accidentally be sending it off into the ether due to some rogue code or something.
Have fun, and let us know how your work with the multi-turn servo goes. the HS-785 has been mentioned a few times around here, though I don’t recall anyone telling us about personal experiences with them. They might be a viable - if not particularly low-dollar - way to get 360 degree rotation for sensor turrets, camera mounts, etc.
There is a separate gears system inside HS-785 instead of multi-turn pot.
I used to make a mistake by sending over than 2000 PWM, which make it spin continuously for more than 10 turn, but it still alive. I also have another of them that is completely dead, it only spin like DC motor, CW or CCW.
What I think is, the gear system are able to handle more 3.5 pot maybe till 10 or 15 turn then it damage the pot somehow.
Hate to bump a tragically old post but this one comes up on search engines allot when looking into multiturn servos.
The HS-785HB is designed for 3.5 revolutions but it does not behave well. So, I took it apart and discovered why. The feedback mechanism is actually a 180 degree pot that is attached to the servo drive shaft via nylon gearing which takes the 3.5 rotations and gears them to 180 degrees or a 7 to 1. Bad positioning error because of reduction.
The real problem is this. The brass pot shaft is pressure/slip fit on to the nylon drive gear. When the pot hits it’s limit it will stop turning but the servo motor will continue to drive in the direction of the ‘off scale’ command. This destroys any registration position the system might have had.
So, bad news is these servos have to be used carefully within their limits or limit switches and a calabration system must be in place.
Good news is they can operate pretty well as continuous rotation servos if you can tightly control your PWM timing and only need forward and reverse.
That might be a good servo for a camera pan.
Alan KM6VV
