How I waterproofed/potted a gripper servo

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Lucas
Posts: 33
Joined: Oct 2nd, 2012, 10:19 am
Location: MN

How I waterproofed/potted a gripper servo

Post by Lucas »

So I'll probably jinx myself and kill this servo on my next dive but it has survived 10 dives so far (~25ft depths) and is still working. I used a basic Hitec HS-311 and slightly modified "The Ultimate Waterproofing Method" found on this page: http://www.societyofrobots.com/actuator ... ervo.shtml

READ ALL DIRECTIONS THROUGH FIRST - many steps must be completed in a short time window.


What you need:
Here were the steps I followed:
  • 1. Opened the servo up and desoldered the motor leads on the circuit board. This will give us room to work and make sure everyone else is completely covered in epoxy before soldering back together
    2. In this servo, there is a potentiometer next to the motor at the bottom of the cavity that needs to move for referencing current servo deflection. In my case, it had some grease on it so I didn't need to add anymore. Additionally, I used a small piece of electrical tape to lightly cover it up. This is just to keep the epoxy from getting into it and binding it up.
    3. This step is quite the balancing act ha :| Fill the cavity mostly full with epoxy, making sure to avoid the contact pins of the motor so they can be soldered against later. While that is settling, coat the circuit board with enough epoxy to cover all components but again keep the motor solder section bare for the time being. As soon as this is complete, set the board back into place, solder those motor leads back up, and fill in any remaining voids with epoxy so everything is potted.
    4. Put the cover on, this should squeeze out any excess epoxy so wipe that up.
    5. Before putting in the screws, we need to fill the gearbox with some kind of oil or grease. In my case, I used white lithium grease. Fill it up as much as possible, and put the body back together, and install the screws.
    6. Add the o-ring to the output shaft and slide on the required horn, being careful to get it tight enough to seal but not too tight where it binds unnecessarily. In my case, I had to also add a drop of RTV silicone to the screw holding on the horn to prevent grease from leaking.
    7. I don't know if it's necessary, but for good measure I went around all the seams on the outside and applied a thin layer of epoxy as another barrier to getting into the servo.
    8. I also gave the control horn a couple twists to verify something wasn't getting glued together that shouldn't be.
    9. Give it a day to dry and test it out!
Unfortunately I didn't take any pictures during this process but I do have some of the finished project (and a hint at some needed updates to my project post :D )

Image

Image

Next step is to try with a higher torque servo. I'll report my findings here, good or bad.
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