I had posted a message earlier regarding making the base servo rotate continously for 360 degrees. lynxmotion.net/viewtopic.php?t=2764
I modified the HS 422 servo, but it obviously does not have control over positioning anymore. This is causing more complications than i thought, as where the rest of my arm goes depends on the exact angle the base has moved from the neutral position.
Now, I was thinking of buying the HS-785HB.I understand that it will not rotate infinitely, but only for 3.5 rotations, but can I achieve positioning accuracy with it?
Would be really helpful if someone could explain the operation of this servo. Also, what is meant by 1/4 scale of the servo?
Thanks in advance.
Looking at the specs for the HS-785HB the input signal range is the same as for normal servos but it has 1260 degrees of output. So you would have to expect the resolution of the servo to be 1/7 that of a standard servo (180/1260 = 1/7). So if your controller is generating say an 11-bit resolution PWM output the adjustment you will get considerably more coarse adjustment per bit.
It may be possible to modify an HS-475HB such that it only operates over the 360 degrees for the normal servo input range. That will no be continuous rotation however.
You may need to consider converting your base to use an encoder that returns absolute position and some sort of gear drive. That might be a project worthy of documenting and making available for others to study/replicate.
“1/4 scale” refers to servos sized for r/c aircraft built at 1/4 scale to real size. The servos are roughly 2x the size and have considerable more torque.
You also have to be careful about having more then 360 degrees of rotation in the base, lest you now require a slip ring for all the cabling. (Slip rings are not cheap, I have looked…)
Thanks!
All your info really made things clearer. I may buy the servo because as I understand, the resolution will change from 0.09 degrees/us to 0.63/us, which is tolerable in my project.
In the longer term, however, an encoder design would be good. I googled some articles on it but I have the project deadline coming up so I don’t see it going that far…
Sienna, I faced the slip ring problem too, but i was able to get some ideas from the forum . My solution for the wiring is to redesign the base such that the servo is upside down. If you keep the horn fixed, the body of the servo rotates which i connected to the rest of the arm. of course, it makes the whole thing a little less stable … and then i mounted the controller on the arm and the battery too and so on.
You should be careful with your assumed resolution. The resolution of the signal sent by a servo controller or received by a servo may not (and probably does not from my experience) equate to the actual mechanical resolution capability of the servo. Below is some discussion on actul servo resolution.
hmm… that thread was pretty interesting…
the measurements were done without any load. So with varying loads the resolution will also vary because the torque generated to move to a new position within 2 us may not be enuf to move the load, hence the servo won’t move. Does that make sense?
or does the motor withdraw more current to move with the same resolution?
I have them here and have done extensive testing with them. They have no useful purpose in robotics as we normally use them. They will hunt and flail without continuous tension on the output.
