How to Tell if an RC Motor is Bad: A Straightforward Guide.

Any RC motor can go bad, especially brushed motors. Brushed motors are cheaper but have wearing parts that do better with regular maintenance. Brushless motors are becoming cheaper and cheaper and last a lot longer. They’re also more efficient than brushed motors with brushed motors being about 75-80% efficient and brushless being around 85-90% efficient.

You can tell if your RC motor has gone bad by checking for overheating, listening for noises, or observing vibrations while the motor is running. Visually, if you take the motor apart and notice dark burn marks on the windings or loose magnets, it’s a bad motor.

Motor magnets attract small steel debris over time which can cause the motor to fail as well. Brushed RC motors and Nitro RC engines require the most maintenance while brushless motors require hardly any.

See a great selection of Brushed and brushless motors and replacement gears here

(Links to Amazon)

Brushed vs Brushless RC Motors

Brushed

These are normally your lower grade RC motors as they aren’t too expensive to manufacture. Brushed motors come in fixed and nonfixed variants, the fixed version doesn’t allow for any replacement of brushes and the motor can’t be modified.

The nonfixed version allows for some adjustments and the brushes can be replaced.

Brushed motors have brushes inside making contact with the motor windings to deliver a current to the motor.

Because there’s friction occurring in a brushed motor, it wears out quicker and a little extra maintenance can go a long way in extending its life.

Brushless

Brushless motors have become a lot cheaper than they were a few years ago. Brushless motors perform exceptionally well and don’t require much maintenance.

Brushless motors don’t have anything touching on the inside to wear it down but debris can still be cleaned off the motor whenever needed to keep it in good condition.

An Electronic Speed Controller (ESC) controls the electrical fields inside the motor in a way that causes it to rotate the permanent shaft magnet inside.

The ESC also controls the amount of power drawn from the battery at any given time based on the torque and speed required.

Brushless motors not only have a higher efficiency than brushed motors but they can also work with a higher voltage supply for super-fast speeds.

The fastest RC cars in the world are electric and outperform even the Nitro engines in terms of top speeds. Brushless motors are nice and quiet so you won’t have to worry about disturbing people that are sensitive to noise.

Brushless motors are lightweight compared to nitro motors giving the vehicle a high power to weight ratio for extreme performance. Unless there are specific reasons as to why you may want a nitro RC, the brushless motor powered RC’s are about the best all-around option especially in terms of low maintenance.

RC Nitro Motors

Nitro RC engines are on another level of performance compared to electric. With almost all the same parts of a normal-sized vehicle, Nitro RC cars are really just like miniaturized monster trucks, rally cars, and racing cars.

So what are the benefits of a nitro engine? The biggest advantage over electric RC’s is that you can run nitro RC’s for as long as you have fuel to top it up with every now and then.

Of course, nitro engines are also more water-resistant compared to electric RC’s. Some people just love the sound they make and enjoy the fact that they can fine-tune nitro engines to a huge extent.

Nitro engines are however very noisy. If you’re planning to run it around your neighbourhood don’t be surprised when some people complain.

The costs of maintaining the engine and refuelling it adds up over the long term and so it’s definitely the more expensive option. Most nitro RCs also don’t have a reverse.

How To Check If Your RC Electric Motor is Bad

First off you can check whether or not you can move the RC motor freely with your fingers. There shouldn’t be that much resistance and the entire turn should be consistent without any bumps. You can even just feel how freely the wheels turn, with the motor connected, if you push it along on the ground.
Now, if everything feels smooth and consistent, brushed motors can be directly attached to the battery to see if they spin, generally speaking, if they spin with direct power from the battery, they’re good. (Just don’t try this with brushless motors as it will not work)
You can test your motor out with another RC to see if the problem still persists.

Check to see if your motor has picked up small pieces of metal like staples, screws, nails, washers, or any other small metal objects as these can prevent the armature from spinning. If you do find anything, remove the debris until it’s clear and you are able to move the pinion gear with your fingers
Unless you have a completely sealed RC motor, spray it out with an electrical motor cleaner to remove any small debris.
Re-oil the bushings or bearings with high-quality bushing oil.
Check your windings to see if there are any that are burnt black.

Open up your brushless motor and check if there are any magnets out of alignment with the rest. Sometimes a magnet can come loose and shift around in the motor. If there are loose magnets you can carefully superglue the magnet back into the exact same place it was without increasing the height of the magnet with too much glue.

How To Check If Your RC Nitro Motor is Bad

To check if your RC Nitro is bad, take it apart and push the piston up through the sleeve, if it stops flush or above the sleeve, it’s worn down.
If your RC motor stalls when running warm/hot and then starts up again once it’s cooled down, it’s a sign of a bad motor.

How To Tell If Your RC Motor Is Going Bad

If your motor is heating up very quickly, it could be going bad

When it starts making unusual noises or gets very loud
If the motor starts vibrating there may be offset magnets inside.
If the performance you’re getting out of the motor is less than it was before, the motor might be worn out.

If you’re experiencing any of the problems above, clean out your RC motor as per the instructions below)

Also you will want to take a look at my article about what to do with an overheating RC motor

How To Dry Test A Brushless Motor

Disconnect the motor from the ESC and isolate all three wires from each other. Attach the motor shaft to a variable speed drill and slowly spin the motor up to 1000rpm and beyond.

The motor should spin easily without resistance with almost no noise. A bit of drag can be expected. Spin the motor with the drill for a couple of minutes while feeling the motor for temperature spikes.

The motor shouldn’t heat up if it does it means something is wrong. Check the magnets inside the motor and make sure none of them has come loose.

If you have a voltmeter you can test all the voltages of each wire. Label the wires 1, 2, and 3. Connect your voltmeter to an AC range and connect it to terminals 1 and 2, run the drill at full speed, and note the voltage.

You can check a Volt meters price here on Amazon.

Do this again for wires 2 and 3 and then again for 3 and 1. All the readings should be very similar at least as long as your drill was running at the same speeds each time.

Check for short circuits between the windings and stator. The windings are all connected to each other, test for a connection between the motor stator laminations and the windings.

You might need to puncher through the insulation to check. The voltmeter should give you an open circuit/infinite reading. There should not be a connection between these two points.

At this stage, you should probably check the motors’ “no-load current” and compare it with the manufactures specification.

This can identify “shorted turns” which will lead to overheating and motor failure. A shortened turn can be repaired by rewinding the motor. Running a motor beyond its maximum current rating can cause shortened turns.

How To Prevent an Electric Motor From Failing / Going Bad

Clean your motor:

Disconnect the motor from your RC and inspect the wiring, make sure the wires aren’t damaged. Wipe the motor off with a cleaning rag to clean off any dust and dirt.

Unscrew the motor separating all the parts so that you can clean them all individually. Make sure you lay everything out so that you know how to put it back together again.

Use a small brush to brush out any dirt from within the motor around the magnets and spray it out with compressed air. Lubricate the bearings of the motor and make sure that they spin freely.

Re-Oiling Brushed Motors Bushings

The bushes on brushed motors need regular maintenance in order to extend their lifespan. These bushings are at the end of the motor and support the armature of the motor allowing it to rotate smoothly.

You should use oil made for electric motors such as 3-in-1 oil (Amazon link). You can buy specialized lubrication from your hobby store as well. You can oil your bushings as much as once every hour of operation and use an electrical spray to clean the motor of any debris.

Re-Oiling Brushless Motors Bearings:

Take the brushless motor apart by removing the screws from the caps to gain access to the bearings. These are the steel circles on the cap that rotate, apply no more than one drop of oil to the bearing, and turn the bearing.

On some motor designs, you may be able to reach the bearing to oil them without removing any housing.

Keep the motor cool:

Keep the motor cooling with heatsinks and fans that are designed for that purpose. Follow this link if you want to see how they look on Amazon. Heatsinks like this one will also keep things cool for a better motor life.

How To Prevent Nitro Motor From Failing / Going Bad

Make sure to empty the fuel tank and run the engine for a moment to also empty the fuel line and engine crankcase.
Clean the exterior of the engine and carburettor with denatured alcohol. Use a small brush to clean everything thoroughly. Then finish cleaning and dry the engine with compressed air. Make sure to wear eye protection at all times while cleaning your Nitro engine.
Remove the air filter from the carburettor and squirt some WD-40 into the carburettor for just 1 second and also into the glow plug hole inside the cooling head.
Place a rag over the glow plug area of the cooling head to catch any WD-40 that might come out and crank the engine with the EX-Start system for about 10 seconds. With a pull starter, pull the starter a few times quickly to circulate the WD-40, repeat this a few times.

Remove the air filter from its housing and clean the element with warm soapy water and allow it to dry.
Clean the base of the air filter by removing it and cleaning it with the soapy water.
After cleaning engine parts, always allow them to dry properly.
Apply around 30 drops of filter oil to your filter element once it has dried. Work the oil into the filter element with your fingers until it has spread all over evenly. Now reinstall your filter.
After attaching the cleaned filter to your carburettor tie it down with a small cable tie.

Put the glowplug back into the engine and reconnect the glowplug wire.

Fuel Filters

If you’re using fuel filters, make sure to clean them as well whenever you’re cleaning your air filters. Make sure they are completely clear of debris and free-flowing. When choosing a fuel filter, go for the options that allow you to dismantle them or at least for ones that are transparent for you to see if there are any problems.

Conclusion

Most of the time you can tell if your motor is bad by checking for overheating, noises, and vibrations. If the motor isn’t providing as much power as it used to, it could be wearing down.

Brushed motors will fail the quickest while brushless motors can last for years without any problems.

Nitro RC engines require a lot of maintenance but can also last a lifetime if they are well looked after. Always opt for brushless motors over brushed as they will save you money in the long term.

If you only have enough for a premium RC with a brushed motor you could upgrade to brushless later and install it in the same vehicle.