Modifying a brushless high speed Servo (Savox) for continuous rotation.

[Hokeypokey]

Hey guys,

I am currently building a camera stabilization system for an university project. The goal is to automatically align the camera (Go Pro Hero 3) with the horizon. I am using the hoverfly gimbal system as controlling unit. The last thing that's still missing is a very fast actuator for the camera rotation, that's strong enough to rotate the camera with its unbalance due to the camera lens not being in the center of the camera housing. I only need to rotate the camera on a single axis. I decided to go with the Savöx servos.

I want to use the SB-2272MG or SB-2271MG Servo. I have some questions before buying these and I hope you can help me out

1) Does anyone have experience with these two Savöx servos?

2) I read about the brushless servos not being able to be modified for 360° continuous rotation due to the magnetic encoder used inside the servo?

jes1111: The new Savox brushless servos (including the 2271 you linked to) can't be modified for 360º rotation. Like the Hitec 7990, they use a magnetic encoder - a magnet on the bottom of the output shaft sits directly above the encoder chip on the PCB. Besides, the backlash in the gearhead exceeds the resolution of the encoder, making this type of servo very "nervous" for this application.

As far as I can see, the hoverfly gimbal only has two pins for the servo connectors, that are for controlling the servo-motor. Do I really need to care about the potentiometer / encoder?

3) How much torque would you suggest for the servo to get the Go Pro Hero 2 or 3 rotated without too much of a backlash? I have big rotations (approx. 60°, that need to be realigned/stabilized) with moderate speed.

4) Is anyone of you using Savöx Servos? Which?

5) I think I want to use a 2:1 timing belt for rotation the camera. What are you using for gear ratios and why?


Thank you very much in advance and I hope to get some interesing answers, that help me getting my final university project working after months.

Christian

 

[Multirotorcraft UK]

Christian

Here is a link to modifying a servo. Its from Photohigher
http://www.photohigher.co.nz/assets/Uploads/External-Potentiometer-Modifications-for-Skyline.pdf

Hope this helps

 

[Bartman]

I tried it on a savox brushless and i don't think they can be taken apart without desoldering the board that is just inside the lower case. It's a lot of disassembly...i went back to the 1268....much easier to modify

 

[Hokeypokey]

Thanks for your replies! I read about the 2272 having a magnetic encoder. If that's true, wouldn't it be enough to only modify the gears and leave the rest untouched?

 

[Hokeypokey]

Okay, I got the Savox SB-2271SG modified for CR. I made a short photo-story to show you my steps. It's possible, not too complicated and works perfectly.

1) Remove the screws, the top and bottom cap and the metal gears.

2) Use a small screwdriver or similar to push the top plastic up and apart from the rest. Do this firmly in order to pull the pins out of the potentiometer. That way you don't need to desolder anything. The three pins came out quite well without destroying anything else. Just some scratches on the aluminium case.

3) Losen the two screws holding the rest of the potentiometer in place and remove it.

3) After that nothing really changed to all the other guides. (Solder two 2.7k resistors to the remaining pins of the ex-potentiometer, cut the gear for CR and screw everything back together.

Here are the photos:

View attachment 7587View attachment 7586View attachment 7585View attachment 7584View attachment 7583View attachment 7582View attachment 7581View attachment 7580

If there are any questions, just ask. I will give my very best to help.

Christian

 

[Bartman]

Christian,

I pried and pried and pried and couldn't get the top plastic frame piece to pop off. I sold two of the four I had so I'll try again with the remaining two.

Thanks for the tips and good job!

Bart

 

[rickmellor]

You have to pry with more force than you're comfortable with. You're ripping the leads out of the potentiometer when removing the top piece, so you're literally ripping it apart. The rest of the internals are strong enough so if you go slowly, the potentiometer should be the only part that gets trashed ... which is ok because that's the part you're taking out anyway.