Good ideas with bad execution, or good execution of what should be bad ideas - an analysis of inferior, off-beat or malfunctioning products, and how other people's failures can help us design better stuff.
Chinese-Made Drill Cheaps Out on Power Supply
Andrew Morris cautions readers to beware when you see one of these made-in-China (shocking, isn’t it?) mini-drills as engineers made some bad trade-offs in the design. “I see many of these things at flea markets and garage sales. Highly useful for PC work, but I think people buy them and then are disappointed with their performance. The motor screams at high RPM unloaded and the small 9 or 12 volt AC adapter is almost useless. It is so underpowered that the drill motor slows to a crawl, not to mention that it has no speed regulation.
The newer ones are using a 12 volt (instead of 9 volt) AC adapter, perhaps to keep them from slowing down to nothing, but they still can’t deliver the required current. The one shown here came with a 12 volt 500ma adapter. The motor needs 2 amps of current for decent torque, with the voltage determining the speed. To get decent (I would say usable) performance from the motor, you have to use something else. Even a 0-12 volt, 2 amp power supply would be a huge help. The speed would slow down under load, but performance would be a lot better than what we have here. Here is a control that I designed for just this purpose. which provides further improvement by adding load feedback. The circuit requires a power supply of 12 to 15 volts at about 2 amps for full performance. Note: some assembly is required. (Perhaps the Chinese should sell a controller like mine as an optional accessory. I can’t even buy parts for what a similar, fully assembled Chinese-made unit would cost.) Anyone who doesn’t want to build the controller can use a variable 2 amp bench power supply to run the motor. It would be way better than the AC adapter. The little motor fits very nicely in the hand while doing delicate work, it’s such a shame that the Chinese cheapened out on the power supply.”Tags: andrew morris, delicate work, performance note, such a shame, variable 2