How a drill stops?

[efik]

Can some one explain to me how a drill stops when releasing the trigger?
I notice that there is some kind of electronic parts involved, but couldn't figure out how it works.
Thanks

[Chris Smith]

Depending on the brand, there are many ways. The simple way is to disconnect the power in, while shorting out the commutator. The commutator while spinning or freewheeling [power off the trigger] generates electricity like a generator and shorting it out in the off trigger position puts a load on it, slowing it or stopping it quickly.<p> Electric trains use this for brakes with a variable dummy load.<p> Add this to the high gearing of the motor,... to the out put speed of the drill,.... and it appears to stop almost instantly.

[efik]

Thanks.
Would shorting out the commutator cause damage to the conduction coil? Should it be using a resistor?

[dyarker]

No. At the instant the motor is switched from power to shorted, the current reverses polarity and jumps up stalled ammount. (Stalled is like when the drill gets stuck.) Motors can handle being stalled for short periods. The current decreases rapidly with decrease in speed. (Faster than when drill gets stuck, and you take 2 or 3 seconds to release the trigger. As Chris said the gears have a fair amount of friction. The drill would stop quickly anyway. It's just faster with electric braking.<p>If the load had a lot of inertia (like a real train), braking with a short would burn out the motor's winding.

[Chris Smith]

Well said.

[efik]

Thanks