servo prolems

Dan E

Just bought A HITEC HS-645MG ultra Torque MetalGear Servo, to replace my Parallax Standard Servo because I needed more torque.

When running my program to center the servo, there is a clicking noise for a few seconds, then it jitters, then repeats this cycle (not the cycle intended).

THe new servo has a pulse width range of 900-2100us, and a pulse cycle of 20ms, just like the standard servo. It's the same size and same rotational range from 0-180 degrees.

Does anyone know why these side affects may occur?

Attached below is the code I used.

New servo - Archive [Date 2011.01.24 Time 23.40].zip

Thanks,
Dan

Duane Degn

I think some servos don't like the 3.3V signal. You might need a level shifter

Dan E

I am using a 5 volt signal from a 5v voltage regulator, do you still the the level shifter would apply?

Thanks,
Dan

Mike Green

You haven't described how you have things hooked up. High torque servos may draw much more current than a regular servo. You may be drawing too much current from the power supply when the servo starts moving. If the Propeller is running off the same power supply, it may be resetting.

Dan E

Your right, both are hooked up to opposite sides of a voltage regulator. I used the circuit that powers the propeller education kit, consisting of a 9 volts going to a 5v regulator that is attached to a 3.3v regulator, and the servo taps off of the 5v with another wire to ground and the 3rd wire to the input signal (3 wires, like the standard servo). I am using a 9volt 1A wall adapter as the initial source. Could I use an additional regulator hooked up to the 9v souce? or would it make sense to use a different power supply entirely?

Thanks,
Dan

Duane Degn

Dan.

By signal I mean the PWM coming from the Prop.

While many of the servos I use work fine with a pulse of 3.3V, some just kind of jiggle in place without the servo arm moving much.

Of course, Mike is almost always right so make sure and take his suggestion seriously.

Duane

StefanL38

Hi Dan,

I made a quick search with google for specs and came up with these two hits
http://www.servocity.com/html/hs-645mg_ultra_torque.html
http://www.servodatabase.com/servo/hitec/hs-645mg

the specs says Required Pulse: 3-5 Volt Peak to Peak Square Wave
so 3.3V should be enough.
Current Drain (4.8V): 8.8mA/idle and 350mA no load operating

so with no load a 1A powersupply should be enough for testing.
I guess WITH load the current goes up to 2A - 4A.
You should use a second powersupply for the servo. You just have to connect the ground of the servopowersupply with the ground of the propeller
otherwise the servosignal is "free-floating" and has no real reference.

best regards

Stefan

Dan E

Added second power source, thanks for the links.

I attached a separate power supply the ground tied to the ground of the propeller but the motor still continues to rev repeatedly.

I think I may take it in to school to see if my professor has any insight.

Thanks,
Dan

Graham Stabler

I think Duane may have the right answer, you may need a level switcher so that the signal from the propeller is at 5v. A transistor and pull up would do it, or a little logic buffer or similar.

Graham

Dan E

Thanks, I'll give tht a try later on.

Dan