I’m trying to build a waterproof enclosure for a standard rc servo motor.
The motor will be submerged in shallow depths (max 5 meters).
The tricky part is realizing a waterproof interface between the servo shaft and the underwater environment.
After searching for a while, I was able to find this approach:
However, it is not clear to me why the bearing above the shaft seal (spring-loaded seal in the figure) is necessary.
Since It’s my first time designing something like this, I kindly ask if anyone else has tried this approach.
Also, here is a cad model developed in onshape that should be a housing for two servos. I did not include the extra bearing(s) as I’m still trying to understand what it’s used for. Housing CAD model
The shaft seal used in the model is this one from 123bearings: 123 bearings shaft seal
Please let me know what you think about the design.
Hi @Funky -
Welcome to the forums!
The second bearing is likely included so that loads on the output shaft do not affect the compresison of the spring-loaded seal. If it was not present, and a load pushed on the motor output shaft radially, nothing would prevent it from compressing the spring loaded seal. This could result in a seal failure!
Blue Robotics is getting closer to releasing a waterproof servo, in the meantime Blue Trails Engineering has a good one available!
@tony-white , thanks for the shout-out, and I agree with you about the purpose of the bearing.
@Funky, on Blue Trail Engineering servos, we use double ball bearings, both on the dry side of the seal. And the seal itself is a 20-cent nitrile “quad-ring” (an O-ring but with a quad-lobed cross section). It works amazingly well. A lip seal like the one you linked to would only be necessary if the shaft were rotating much faster than a servo rotates.
