Impulse DIY fuction for cordless screwdriver power tools

[smilem]

Hello, I have an idea to make the impulse function on a makita brand cordless screwdriver.
It is very handy to unscrew old bolts, or to drill to shiny surfaces like tiles.

Unfortunatelly the impulse is metabo "inovation" - if you can call pulsed power to the motor
innovation. It is available on few cordless drills, and I have one of them that's when I understood how handy this is.

You can see a video here how the impulse function works

Is is possible to design a simple circuit with power fet, etc to pulse the power to the motor?
I'm sure a power fet, capacitor to select pulse cycle length and some other parts would make this
doable for DIY project.

 

[(*steve*)]

I would start by looking at a PWM motor controller and slow the frequency right down to something between perhaps 4 and 10 Hz

 

[smilem]

I would start by looking at a PWM motor controller and slow the frequency right down to something between perhaps 4 and 10 Hz

AFAIK the motor controller is in the switch of the screwdriver, it is very small and I think they build them to not be serviceable to protect from dust etc. Why not use a MOSFET on motor or battery pack with 555 timer it would be easy ?

 

[BobK]

I probably don't know what I am talking about , but I suspect the impulse mode is more than just turning the motor on and off quickly. I suspect it is increasing the torque by having the motor running, then coupling it to the bit only in short bursts, the inertia of the moving parts gives a burst of torque that will not be duplicated by turning the motor on and off.

Bob

 

[smilem]

I probably don't know what I am talking about , but I suspect the impulse mode is more than just turning the motor on and off quickly. I suspect it is increasing the torque by having the motor running, then coupling it to the bit only in short bursts, the inertia of the moving parts gives a burst of torque that will not be duplicated by turning the motor on and off.

Bob

Did you see the video? That is motor being turned on and off, the power on switch like on any drill control the speed - torque. The more you push the switch the more the drill turns in pulsating action that is longer because speed is higher.

It is not soft starting the motor, you can see sparks on the motor brushes if you push the switch and higher current starts to turn the motor.

 

[smilem]

Here is schematic I've built using google and some information about MOSFET drives on vibration motors, should apply to DC motors too.

Any suggestions, improvements?
I need to select component values that is safe to use, any suggestions?
The drill switch is rated at 12A 24V, the battery is 10.8V Li-ION

 

[(*steve*)]

Yep, looks (from the video) exactly as if the pule mode just turns the thing on and off. The duty cycle looks quite high and does not appear to be related to the speed.

So it appears to be a slow modulation of the PWM signal applied to the motor.