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300 Watt Scooter Motor Mod - Written and photographed by Aaron Knight


The 300 watt motor, we've all seen it over at - Oatley Electronics,
and some of us have looked at them and found them suitable for our robotics projects, like Team Nexus's

and Team Unconventional Robotics's

These are a low revving motor with plenty of torque while maintaining a minimal amperage draw at 24 volts. Some spec on these motors are shown below.

These specs are taken straight from the Unite Motor Company website who manufacture these motors, and install them into there Dolphin Scooter series.

This guide is to help those wanting to pull apart these motors for maintanence or for other mods. Pulling apart one of these motors and rebuilding them is a pain in the peverbal without at some mods. I know, I tried

The Modification:

Well enough of the boring stuff. Let's start pulling these suckers apart! You'll need the following tools to for this modification:

* Drill press or XU1 cordless* 2.5mm drill bit * Stubby Star screwdriver * 4 assorted paper clips * 12mm ring spanner * Marker pen * Butane Torch (Optional)

Beginning of the fun!

First we need to remove the face place screws. These suckers can be hard to get out, take your time so you don't strip them. Remove the nut and sprocket with the ring spanner while your at it. You may want a butane torch to burn of the epoxy on the nut as it makes it hard to remove with the glue still on the thread.

When your finished, it should look like the above.

Now remove the front plate

Your motor should now look like the above.

Now remove the back plate like above, remove it gently to prevent the brush springs from fying everywhere!

Now your motor will only have the armature magnetised to the magnets inside.

Now you'll have your motor laying all over the place :P DO NOT lose any of the peices!

This is where we will first start modifying. This is the back plate with the brushes

Push the spring and brush back into the holder, pushing the braid back with it. This shows the maximum distance the brush can sit back in the carrier and will help us determine where to drill the holes.

Now use the marking pen to make a small dot just infront of the loop of braid. This is where we will drill a hole.

Here you can see where I marked with the marker pen. Repeat this for each brush.

Now to drlll the holes, I found it easier if I sat the brush housing into the magnet ring shown above.
I'll be writing a magnet glueing mod tutorial for this motor

With the brush housing sitting in the magnet ring, it makes the housing sit level, which helps for drill holes square and accurately.

Drill through the garolite, only apply a small force while drilling garolite as it will crack if you press too hard. Let the drill cut at its own pace. Drill all the holes before mving onto the next step.

The brush holdeer should now have these holes in it. This will be the only outward visible modification to the motor.

With the 4 holes drilled, it's time to move on top pinning the brushes into place for re-assembly.

Paper clips are your best friend for this job. Mig wire and rivits work well too.

Bend the end of the paper clip like above.

Push the brush and spring in with your finger, and hold it there.

Make sure the loop of braid is behind the hole you drilled or this process will not work.

Now insert one of the paper clips into the hole aligned with the brush your holding in place.

The paper clip should come through the hole and stop against the braid, which holds the brush into place.

Repeat this paper clip process for each brush until they are all locked into place.

A view from the back. I'm color co-ordinated as you can see.

Now insert the armature back into the brush housing. This is a lot easier to do now that the brushes are locked. No more jamming your fingers between the brush housing and the commutator.

The armature safely back into it's bearing and brushes.

Remove the paper clips while holding the armature and brush housing together to prevent them from seperating.

Make sure this grommet with the power wires is in place.

Now put the magnet ring slowly over the armature. Push down on the armature with your free hand to stop the armature jumping into the magnet ring. If this happens, you'll be back putting paper clips in brush holders and working your way back here.

With the magnet ring placed on to the armature and brush holder, rotate it till the groove on the magnet ring matches the notch in the brush housing. I'll look at writing a timing mod tutorial for this motor in the future

Your motor should be half rebuilt by now.

Now install this small metal shim on top of the bearing.

Align the notch on the front face plate (Above) with the groove on the magnet ring (Below).

Close up of the groove.

Your motor should look like this with both the magnet ring and face plate matched correctly.

Now time to put the screws back in. This job is the hardest of all. When putting the screw in, tilt the screw so the head is facing the shaft and the end of the screw is rubbing against the magnet ring. If done correctly, your screw should sit up 5mm like shown above, if not, you'll be fishing around for a while trying to get the screw in.

I become annoyed after 5 mins of fishing for screws that sat flush with the motor when I tried to get them to thread in. So I came up with this little tool. That's right, a piece of cardboard! When you push the screw in and get it to sit up 5mm, insert the cardboard under the head of the screw. thi stops it from going all the way down if the screw slips of the hold inside and will save you going insane when you try fishing the screw back out!

When the screw threads in a few turns, you can remove the cardboard and finished the job like above. Now repeat for the other screws.

Only a few small things to finish now.

Put on the metal spacer before the sprocket.

Slide the sprocket and spring washer on to the D shaft.

Tighten the nut up and your finished! Easy as 3.14 (Pi)

Your motor completely modified. Only the 4 holes show that it's been modified. Enjoy!


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