10 Dollar Drill
$10 Harbor Freight Drill — How the heck can these guys sell a drill for $10?
Austin paid $10 for this drill at harborfreight.com (shipping was an extra 6 bucks). It’s a 14.4V cordless drill. And it’s blue.
The major components are straight-forward enough: drill body, removable/rechargable battery, some driver bits.
The main body is molded in two shell halves and joined with plastite screws; the black grip piece covered some of the case fasteners.
Meanwhile… while Austin works on the main handpiece, Tony attacks the battery pack:
Again, screws are the preferred method for joinery.
The battery packs 12 NiCd cells in a tight little package. All of the cells are prewired together and terminated at the clip interface below. The whole pack kinda folds up like origami into the plastic battery case.
12 Cells at 1.2V / 1000mA-hours each. Made in China.
Some of the molded parts had the mass stamped inside. A nice touch but we’re not sure where that would be useful. Perhaps to help with plastic material inventory.
The motor was a Chinese motor, very similar to a Mabuchi motor. Both had size RS550 in their part numbers and the motor has virtually the same form-factor. I’d guess the Chinese motor was interchangeable with the Mabuchi. Tony found the motor manufacturer/distributor here: Jin Ma Zhi RS550-S
Getting the chuck off was hard. There was a Phillips head fastener in the chuck – just try to turn it!
See the screwdriver shaft bend and twist…!
We gave up on that end and removed the motor from the rear of the drivetrain instead:
The motor had a metal pinion that acted as the sun gear – the input to a two-stage planetary reduction. The first stage is plastic, second stage is metal. All of the stages share the same ring gear – the ring gear made the housing. For what it’s worth, the planets are 18-tooth; the second sun gear is 9-tooth. Also note how the planet gear bearings get beefier and more robust as the speed goes down and the torque goes up!
At the output of the gear reduction we found balls – used in clutch mechanism.
Austin thought he could drill out that fastener we were talking about earlier…
We really wanted to get that shaft off of there. The chuck might be cool, but we wanted to look at the clutch. How to separate the two?…
This is looking dangerous…
Rock and roll.
The clutch mechanism…
All in all, there are some good examples in this drill of low-cost power transmission and reduction. Some of this will likely be applied as we design LEV shift mechanisms.
