Replacing a HubSan Q4 Motor

The front left motor on my HubSan Q4 stopped working recently, so I bought some new motors and replaced the broken one. This is a step by step guide to how I accomplished the repair.

The tools you will need to make the repair

The tools you will need to make the repair

In order to make the repair, you need a soldering iron and solder, a screwdriver, tweezers, and pack of new motors. A small pin vice might also be useful, but fingers can work just as well.

Remove the propeller by pulling it gently upwards. They usually come off fairly easily. If it doesn’t then use a soft plastic (or balsa?) implement as a lever between the top of the motor and the base of the prop hub.

Pull the propeller off gently with your fingers.

Pull the propeller off gently with your fingers.

Next, carefully release the motor.

Release the motor from its mount.

Release the motor from its mount.

And push the two white mounting clips inwards to release the white plastic motor mount from the PCB. This leaves the motor free, apart from the two soldered power wires. This is done after lifting the motor upwards and out, otherwise there isn’t enough room for the clips to move in and clear the PCB.

Push the two white plastic clips inwards.

Push the two white plastic clips inwards.

Next, desolder the two motor wires, noting that white is (+) and black is (-), although it’s identical to the other motor. Don’t use too much heat, it should only require an instant to release the wire. This is where the reason for removing the white plastic motor mount first becomes apparent. It’s too close to the solder pads to avoid melting it with the soldering iron otherwise. The picture below went a bit wrong as I accidentally clicked the motor back into place when I put it on the desk to take the picture. Just pretend the motor is hanging through the hole as in the previous shot.

Desolder the old motor.

Desolder the old motor.

Remove the old motor completely and mark it as defective so it won’t get confused with any of the new ones. Select the correct type of new motor from the pack. In this case it’s the black and white wire motor, not the red and blue one.

The new motor and the defective one it replaces

The new motor and the defective one it replaces

Insert the new motor into the plastic mount, making sure to get the wires coming out of the correct side and from the right hole. This is what the tweezers are for, as it’s a very fiddly operation.

The new motor goes into the mount.

The new motor goes into the mount.

Note the position and orientation of the motor wires.

Note the position and orientation of the motor wires.

Now solder the new motor in place. The pictures with the soldering iron are actually posed for the camera. There are two reasons for this: firstly, I don’t solder on a piece of white cardboard and, secondly, I only have two hands. The soldering iron is cold in the photos and propped up precariously on its stand with me holding the tweezers. The pictures show the motor, NOT clicked into position, but held by its powerful magnets against the metal pin vice. This will work well, but I found it just as easy to hold the job with my fingers and solder it that way. Obviously, not burning your fingers is the most important point if you choose to hold it, so only do this if you are confident with a soldering iron and do it every day. If you press the wire down against the PCB so that the exposed part sits on the solder connection, then you can just about get away with it without burning yourself. Otherwise, use the tweezers to press the wire against the PCB and use as little heat as possible. A little solder run onto the wires and pads always helps.

cpa1

Carefully solder the motor wires onto the correct pads.

cap2

The motor isn’t clipped in place at this point, I’ve just poked the wires through the hole in the PCB for now. Magnetism is holding it to the pin vice.

When soldering the wires, make sure to get the direction of wire entry to the solder pad correct. This will aid with tidying up the wiring afterwards and make sure it doesn’t catch on anything. They both point inwards like in the picture.

It's important to point the wires inwards.

It’s important to point the wires inwards.

At this point I like to test that the electrical connections are all good and that it all works as expected. In order to see the motor spin, I’ve attached a piece of tape to the spindle.

The tape allows you to see the motor spin. Buzz the throttle lightly and see that it works.

The tape allows you to see the motor spin. Buzz the throttle gently and see that it works.

That’s almost it, but you have to release the motor from the plastic mount as if you were going to take it out, then push the white mount fully into the PCB before replacing the motor. The reason for this is that there isn’t enough clearance for the mount to go into the PCB with the motor taking up all the space inside. Also, note in the picture two small plastic lugs which must be carefully located into a cut-out in the circular PCB hole. If you look at the circular hole carefully, you can just see the cut-out to the left of the “B” where the two wires are disappearing underneath.

Don't push all the way yet!

Don’t push all the way yet!

Release the motor to make space to click the mount in.

Pull the plastic over the top of the motor apart while simultaneously pushing the motor upwards to gently release it.

Pull the plastic over the top of the motor apart while simultaneously pushing the motor upwards to gently release it.

Now push the white motor mount downwards to click it fully into place. The white plastic is quite brittle, so it’s important not to use too much force. Slip the motor to one side before pushing down so that it reduces the stress and the lever effect as the clips go in. Otherwise you can crack the mount. In other words, make sure the motor isn’t pushing the top lugs outwards when you push the mount down into place.

The motor is now released.

The motor mount is now in position and the motor is about to follow.

cap

A different view showing how the mount fits into the PCB.

Finally, push the motor back into place and fit the propeller.

The motor back in position.

The motor back in position.

Push the prop back on.

Push the prop back on.

And we’re ready to go flying again!

TX on, RX on, blinking, bind, ready to go.

TX on, RX on, blinking, bind, ready to go.

Everything works and it lifts up into the air again. I’ve never managed to film myself flying it yet, because every time I try and get the quadcopter into the camera’s view I lose control and crash into something.

Also, don’t forget that the trim is likely be a long way out after changing the motor, so you might want to do a trim reset first on a level surface. Mine was drifting back and right quite a lot, but I was just happy to be flying it around again. I have a knack for finding the neutral operating point after years of test flying other people’s models and have a habit of just flying models the way they are. I’m not sure if that’s a strength or a weakness, but I have had a few occasions where I’ve flown a model seemingly perfectly, then, when somebody else flew it after me, they nearly crashed. There was that electric glider that went vertical immediately after launch which was a bit of a shock for the pilot, but I probably shouldn’t mention that.

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