Disassemble Old Cordless Drill

While working on my NEXTEC Dustbuster project, I took the work-in-progress to various local maker meets to as a show-and-tell subject. This inspired another local tinkerer to bring a really old cordless drill for a compare-and-contrast session. It hasn’t run in years so nothing was risked by taking it apart. Which we did.

We see a motor that’s roughly in the same class as the motor in my Dustbuster. Instead of an air-moving fan directly attached to the motor output shaft, we have a simple reduction gearbox instead of the planetary gear popular with modern counterparts. Other missing convenience features common in current generation products include a torque-sensitive clutch and key-less chuck.

The most surprising part of this old design is how they implemented the two-speed mechanism. The trigger moves a switch into one of three positions corresponding to “off”, “low”, and “high” speed. Obviously “off” is an open-circuit and “high” speed connects all five (six?) battery cells to the motor. It’s the “low” that was a surprise – as far as we can determine, it connects three of the battery cells to the motor and bypasses the rest. This will certainly send less power into the motor, but it also results in uneven discharge pattern for the battery cells. Such behavior is considered absolute no-no with modern lithium-ion battery cells, and it couldn’t have been very healthy for these old NiCad cells, either.

In theory this drill could be revived with a battery transplant, or maybe upgrade to two-cell Lithium-Ion power. Whether it’ll happen depends on the owner, who should definitely find an alternative implementation for variable speed.

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