RF Servo's Problem


Active Hunter
I have a servo installed in my bucket to move my rangefinder up and down and it works great!..... but I find that sometimes, usually when I'm looking down towards the ground, when I raise my RF, and stop it at the top, it will slowly go back down again a little bit. It's like the gear ratio in the Servo is not strong enough to hold the weight of the RF (which is hollow resin without LED's).

I am using the Hi-tech HS-77BB low profile servo powered by 2 AA batteries.
What model Servo are you using?
Can you change the gears in the servo?

Also sometimes the servo will raise the RF then the RF post stops when it contacts the ear cap and kinda bounces off. How do you stop that from happening?


Gator Fett

Active Hunter
I am using the Hi-tech HS-77. Which looks like the old model # for the same servo. I am using the Hyperdyne kit, which has (2) 9V batteries. One for the servo and one for the remote control board. Since you are using (2) AA's you only have 3 volts of power. It may be a power problem, not a gear problem.

I don't know if you can change the gears in a servo. I took a dead one apart to see what was in there, but I don't think I could have got it back together. :facepalm

Every once in a while mine acts funny at the top of the ear cap too. I usually try activating it a couple times, and that usually clears the problem. If that dose not work, I take my RF stalk off the servo end, and activate the servo without the RF. I let the servo return to its "up" position, then reattach the stalk.



Active Hunter
Gator Fett,
Thanks for the reply, I wondered if increasing the voltage would help. The sevo is rated for something like 4.5 volts. But the problem really is when the servo is not powered......
Aslo I would think increasing the voltage would just speed up the RF movement which would increase the bouncing off the ear cap problem.

.... I guess I could just keep my thumb on the button to hold the RF in the upright position until it is stable. But that may also cause it to bounce a bit.

I will try to hollow out the RF a bit more to lighten the load.... I guess I'll never get LED and a mercury switch in there then?

HS-77BB is a ball bearing servo, HS-77 has bushings. I don't know anything about the hyperdine kit...does it have endpoint adjustments for the servo? If it does you can tell the servo where to stop for each direction of movement. As for the batteries, every servo I have seen in the R/C industry operates best off of 6 volts (4 AA batteries). And yes, the voltage affects the speed, torque, and holding/centering ability of the servo. Let me do a little digging...I've been doing RC waayyy longer than Boba Fett so I'll see what I can come up with. :cheers


Active Hunter
Thanks Flatspunout. That would be great.

I sent the same question to the Tech Support guy at Hi-Tech. He said to bring the voltage up and that will help. I just can't figure how it will help since the problem is when I am not applying power to the servo...... unless it draws power to keep the servo in one place when ever a battery is installed?? But I didn't think it did that?

Anyone else have this problem?
The servo is always drawing power (unless the switch is off), especially in this case where it is not allowed to return to center. From what I can gather from the Hyperdyne site there are no endpoint adjustments, just 90 degress of movement, which means that the servo (and rf stalk) must be able to move through a 90 degree arc without binding or hitting anything AND must be oriented properly on the servo output shaft so that when the board sends the signal "down", the servo can go to the full "down" position and likewise for "up". In other words, make sure the rf stalk is at 0 or 90 degrees relative to the servo (depending on how it is installed) in both the up and down positions. Hopefully addressing these 2 issues will stop the bouncing off the earcap problem you described.

I'm with the Hi-Tech guy on the droopy rf issue...more power. The Hyperdyne site actually recommends a 9v battery to power the board and servo so at just 3 volts you are definitely underpowered. I'm guessing the board has a voltage regulator for the servo to keep it at 6v. Hope this helps!

-rocky b
oops...I just assumed you were using the HD kit but I just took the time to carefully reread the original post and noticed nowhere in it do you mention HD!

Anyway, the same rules apply, just make sure that servo is getting 6 volts! And I would think that working LED's shouldn't be an issue...that servo should have plenty of grunt with the right power source!