motor exposure question

DIY Builds
#1

I’m admittingly surprised how much water, mud and debris the motors on the MTBs seem to be able to handle. To my non ME engineering side, seems like these conditions will kill a motor in a short period of time. Especially exposure to water. Does it require frequent disassembly / cleaning of the motor interiors? Maybe just a regular blasting with compressed air? Or is the exterior shell of most motors that good at protecting it from the abuse?

While certain parameters for motors vary with manufacturers, they all seem to employ the same casing / materials… at least to my eye.

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#2

The nice thing about brushless motors is that they are naturally water resistant, all the coils are insulated so they can get wet without immediate issue

And because they spin so fast you don’t get much large debris going in, usually just a thin layer of dust on the outside

If you are feeling a little on the worried side go for a mostly sealed motor or get a mesh cover for it, or if you are really worried you can get an inrunner, but it’s not going to be an issue for the majority of us

The other thing you can do is to battle harden the motor, that will protect all the wires from anything that gets in that tiny gap

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#3

The sensors are far more fragile but if you don’t use those, the motor itself is rather waterproof and resilient. Water shorting out a winding will have a much higher resistance than the winding itself and should have little to no effect on the operation.

The bearings are the only consumable and there are ways to extend their life by keeping them oiled.

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#4

Wow - I didn’t know any of that. Thanks - good to know!

#5

Same thing! :grinning: Wow - I didn’t know any of that. Thanks - good to know!

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#6

Flipsky motors are a pretty solid choice these days, they are solid quality for the price, and they are mostly sealed (they claim to be battle hardened but I haven’t cracked mine open yet)

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#7

They do seem to be reasonably battle hardened but not quite all they way to the ends of the magnets

There was discussion recently of this being the source of a noise in a certain rpm band.

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#8

As mentioned above, brushless motors rarely if ever have any issues with water or debris, at least electrically, and can even be run submerged with little issue.

The most susceptible components are the sensors (hall and temperature), and the bearings.

Since the sensors have a constant 5-volt DC supply going to them, they’re somewhat susceptible to corrosion if exposed to conductive (salty) water if they haven’t been completely waterproofed or encapsulated in conformal coating or epoxy.

The bearings are usually made of a fairly high-carbon, low-alloy steel (AISI 52100), which while extremely hard and wear-resistant, isn’t all that resistant to rust and corrosion. There are stainless, coated, and even ceramic bearings, but they’re far less common and more expensive.

As long as you make sure to dry the motor out thoroughly after it gets wet, and rinse off any potentially salty or corrosive contaminants (salted roads are awful for cars and PEVs alike), you should be fine.

A little water now and then won’t hurt them, especially if it’s fairly pure water - it’s long periods of exposure and salt that really do a number on them.

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#9

This.

I’ve found that after riding in salty wet conditions, hosing off the motors [with fresh water] while running them IMMEDIATELY AFTER the skate is over, helps immensely in limiting nearly all damage.

#10

Pro tip, if you tighten your set screws when they are frozen they are hella tight when they warm back up :joy:

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#11

That’s big brain shit.

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#12

Also if you freeze your motor shaft you don’t have to hammer it in after servicing the motor, makes everything smoother.

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#13

thermal expansion for the win

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#14

I did something dumb and rode through salt water then didn’t wash off the board and left it wet. The BN 6384 was seized the next day…I was already ready for a ride so gave it some torque back and forth then forgot about it. Still waiting for it to start wailing.

#15

There seems to be a widely held misconception that water is antithetical to electronics. It’s not, at least not nearly as much as most people think it is.
Very clean, pure water (deionized, for example) is actually a surprisingly good insulator.
It’s when you have things in there other than pure water (salts), that things can get hairy.

In general, if a piece of electronics is powered off and has no battery, it’s perfectly okay to expose it to water, even dirty, salty, or otherwise conductive water, as long as it’s thoroughly and completely clean and dry before you apply power to it again.
This is one of the reasons removable batteries should still be a thing in phones! If your phone takes a dunk, and you pull it out, take the battery out of it immediately, rinse it, and then leave it sitting in a bowl of rice or desiccant for a day or two, chances are good that it will be completely fine afterwards.

I’ve actually gone so far as to remove the keyboard from my laptop after spilling soda on it, take it to the kitchen and give it a good scrub under hot water to remove any soda residue, before drying and reinstalling it. Lasted me another two years after that IIRC, and it wasn’t the keyboard that eventually killed the laptop.

Even with power running through things, in most cases you won’t see sudden death. You can get current leaking where it’s not supposed to, and that can mess with some things, but a lot of digital circuits will just ignore that because it’s below a certain threshold.

The main issue with water and running electronics is corrosion over time. That current leakage will strip metal ions from one side and deposit them elsewhere, eroding pads, leads, and traces, and can even form metallic conductive dendrites that can cause a proper short. The more salty the water is, and the closer the traces are, and the higher the voltage between them, the worse this can be. This usually takes minutes at least, and hours, days, or even weeks at most.

I will mention that this all mostly applies to low-voltage electronics, not line voltage (110-220+VAC). Water and that kind of electricity can be really bad, because the high voltage can cause enough current flow to electrocute a person if they accidentally make a circuit with the water and their body.

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#16

That’s not ideal, but my standard procedure after that is just to run it. The bearings usually loosen up with use. Just turn the wheels and/or motors with your hands until they spin without too many crunching noises. Then ride away :stuck_out_tongue_winking_eye:

You probably knocked a HUGE fraction of their life off in just a day though. :grimacing:

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#17

Don’t do this. Just skip the rice and put it on a towel.

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#18

There is nothing wrong with putting it in rice. It does draw water out and even if it didn’t, it doesn’t hurt. You can even cook and eat the rice after. :joy:

#19

I respectfully disagree, it can hurt (slow down the drying out process). This can cause additional damage to anything that is reacting to the water (rusting, etc.).

Rice (and any other substance) cannot possibly “pull out” moisture from something. There is no suction mechanism, no inhaling of air to allow extraction of moisture.

All rice (or silica gel) can do is absorb incredibly tiny amounts of water vapor that has already evaporated from the thing that is wet. Consider that carefully though…if the moisture has already evaporated from something that was wet, and that moisture is already in the air, then why go through the trouble of trying to absorb it? Just blow the moister air away.

Placing something wet in a container with rice actually slows down the drying of the item. The rice blocks any air flow, can only absorb tiny amounts of moisture (badly), and creates a high-humidity layer just outside the thing that is wet.

This higher local humidity level slows down evaporation and thereby interferes with drying. You can dry the item much, much faster by shaking out/off any excess moisture and placing in front of a fan.

The fan blows away the moisture that has evaporated and leaked out. This lowers the local humidity level, encouraging more evaporation. The fan’s air flow could also directly blow on the moisture, significantly speeding up evaporation.

If anything seems to have dried out (has anyone ever opened it up and confirmed that?) and works it has done so in spite of the rice, not because of it.

I’ve done very carefully controlled tests of this to confirm the science. Leave the thing out and grab a fan. You can cook and eat the rice that much sooner. :slightly_smiling_face:

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Water invasion sensor idea
#20

But could you cook and eat the fan afterwards?

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