We have one Makita rotary hammer drill in the club already, but for this expedition we wanted another so we could have two teams bolting at the same time. Jarv already described the LiPo batteries in a previous post, and he also an excellent blog post on modifying Makita drills to add long leads for external batteries. We bought a new drill off eBay for £99 (all the cost is in the batteries, so 'naked' drills are quite cheap). Having nothing better to do with my Sunday evening, I decided to crack it open and poke around inside.

Disassembling the Drill

Under the two black plastic caps is this little copper cap holding the carbon brushes in

First, I pulled out the carbon brushes. There are two, hiding under two layers of black plastic caps that you can pry out with a flat head screwdriver.

The carbon brushes are on little springs and like to fly out at random

Once they are out of the way and stored in a little pot for later, I removed off the four long screws that hold the motor and drill chuck in place.

The front part of the drill is held in with four long screws

After switching the drill from hammer mode to drill mode to lock the hammer mechanism you can pull this section out - the large permanent magnet in the back section puts up a bit of a fight. Then I removed the seven short screws that hold the two halves of the back section together, revealing all the wonderful electronics inside.

Lots of wires inside the drill, many of which I have no idea what they do
.

Adding the external leads

More Wires

There are two nice holes left exactly as if Makita wanted us to attach some long wires to their drill. I found some thick multi-strand wires in the caving club stores, cut about 1.5 m off, and soldered them to these attachment holes. I used a soldering iron to melt a hole in the casing for the wires to pass through, and tightened two cable ties to the wires to stop them being yanked out.

Blue cable ties just inside the casing to stop the wires being pulled out

Unfortunately, the drill refused to work.

After pulling apart our old drill and checking it over, I noticed there is an additional contact on the battery on our new drill, and I had no idea what it's supposed to do. After umming and ahhing for a bit, I decided to do something stupid and short this extra contact to the positive terminal of the battery, and suddenly the drill sprang into life. So that's a win for mindless experimentation. Inside the case this contact leads to a yellow wire that I cut and soldered to the positive terminal.

Seemingly extraneous yellow wire soldered to the positive terminal

I've been told by Jarv that this could be a wire leading to a thermistor on the battery that makes the drill cut out if the battery overheats - for our purposes, it's an unhelpful safety feature.

Putting it back together

Reversing the steps above gets the drill back together nicely - it's worth cross tightening the screws to keep the watertight seals on the drill in proper working order. Now we have two working drills for New Zealand, and I have learnt far more about the internals of this specific drill than I ever, ever wanted to know.

Jack Hare