Waterproofing of brushless motors

If you've ever tried it, you probably know that a regular brushless motor from a model airplane can work underwater. But when you test it in something like salty seawater, you’ll quickly realize that these motors aren’t built to last in such harsh conditions. The main issues are:

• Corrosion and Rust
• Electrical Shorts
• Wear and Tear from Particles in the Water

To make a cheap and reliable underwater motor, we need to address these problems. Here’s how:

1. Preventing Electrical Shorts

This is the easiest problem to fix. The wires inside the motor are coated with enamel, so they won’t short circuit unless damaged. The only exposed parts are the three solder joints where the wires connect.

Solution:

Cover the solder joints with resin and let it dry. This is a simple and effective way to prevent shorts.

For motors without solder pads, wrap the joints with heat-shrink tubing. You can also add hot glue before shrinking the tubing for extra protection.

2. Dealing with Corrosion

Corrosion is the trickiest issue to solve. Saltwater can eat away at the motor’s parts, causing it to fail.

Motor Housing:

Most motor housings are coated or plated to resist corrosion. Using materials like stainless steel or anodized aluminum helps too.

If you really want to go all out, titanium is the best choice because it doesn’t corrode at all.

Bearings:

Bearings are especially vulnerable to corrosion, which can cause noise, vibration, and even make the motor hard to disassemble for maintenance.

Solutions:

Use stainless steel or ceramic bearings. Ceramic bearings are great because they don’t corrode and can even lubricate themselves.

Another option is high-performance plastic bearings, but they might not handle high speeds well.

If you’re handy, you can use a copper bushing, but it might be noisy when running in air.

Motor Core:

The inner part of the motor core (made of silicon steel sheets) is usually coated with insulation resin, but the outer part isn’t because it needs to fit precisely.

To protect the outer part, you’ll need to treat it with something like lubricant or waterproof coating. Regular maintenance is key to keeping it in good shape.

Coils:

The coils are the heart of the motor, and if their enamel coating gets damaged, the motor is pretty much done for.

Protection Methods:

You can coat the coils with resin, glue, or spray paint (like the white coating in the picture).

Transparent resin works well too, as shown in the image.

3. Preventing Wear and Tear

Underwater particles like sand or dirt can get inside the motor and cause damage over time. To avoid this:

Make sure all openings are sealed properly.

Use bearings or bushings that can handle debris without failing.

Summary

To make a brushless motor work reliably underwater:

Prevent Shorts: Cover solder joints with resin or heat-shrink tubing.

Fight Corrosion: Use corrosion-resistant materials for the housing, upgrade to stainless steel or ceramic bearings, and protect the coils with resin or paint.

Reduce Wear: Seal the motor to keep particles out and use durable bearings.

With these steps, you can turn a regular brushless motor into a low-cost, reliable solution for underwater propulsion!