Let's Make Robots!

Power toool motors - worth scavenging?

It's been a while since I spent any serious time at LMR, or indeed building robots. A pressing need to totoally renovate a Victorian house has taken priority so that I can generate enough money top pay the mortgage interest when rates rise again !

However, a by-product of the rennovation is that I retired some of my old power tools. They worked, but having moved up from occasional DIY to extreme DIY I wanted tools with more grunt. So,sitting on my desk I have a hammer drill and a jig saw - both mains powered - and a cordless screwdriver. I have posted these on Gumtree but no takers, so I'm wondering if I could strip the motors out for future robot projects. I see two challenges here and am looking for ideas/assurance that it's worth the effort to keep these rather than bin them.

Challenge 1: a power source. The drill is a 240volt, 400watt device, and the saw 240volt, 350watt. How can I power these from batteries?

Challenge 2: speed. The drill operates at a fixed speed of 3,100 rpm. The saw has "electronic speed control" - whatever that is - but appears to be based on 3,200 rpm. Somehow I need to get this down to something that's more useable - I have this mental picture of a robot head whipping round at 3,000 rpm :). A gearbox or step-down of some sort will be needed. Does anyone have experience of finding and fitting gearboxes to old powertool motors?

The cordless screwdriver is a 3.6volt device delivering 180rpm under no load. This looks a lot more useful.

LMR seems to have had a makeover since I last visited - I think it was being hinted at in The Pulse. Haven't searched for new features, but have noticed a few changes to the logo. Looks good.

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In the robotics team, we sometimes use Drill motors (with gearboxes) and modify them so we get exactly the performance we want. Make sure you get drills with voltages near 12VDC.
It is worth. But don't use AC drills and saw's, its complicated. I have similar idea myself, but i plan to use NiCd battery powered drill engine. I buy a cheap drill and I get one 12V engine with gearbox, a 12V NiCd battery and a charger. Full set! Only H-Bridge is missing.

If I was going there, I wouldn't start from here!

Question is, how can I use what I've got, not how can I get a cheap motor. :)

As an Electrician, all the AC powertools I repaired actually used what they call a "Universal Motor". Unlike the DC motor you find in many toys, a universal motor has electromagnets rather than permanent magnets. This allows the motor to opperate on AC because the magnetic field of the stator reverses polarity at the same time as power to the rotor changes polarity.

To boil this all down, they should work on DC nicely if you find the right voltage. Here is an instructable on the subject.

WARNING: no garantee that electronic speed controls will be happy with DC. 

Thanks for the Instructable. It seems to suggest that I'm going to need a set of car batteries to provide enough juice to run the motor. Might work for a static device - perhaps a robot arm. But if it's static why not just plug into the mains supply?

Drill GutsI cracked the drill's case - in the name of science, pursuit of knowledge, et. The A/C goes pretty much straight to the motor. There's a white "component" at the base of the hand grip, but I think it's some sort of smoothing capacitor. Or possibly it supresses spikes and noise going back into the mains supply. The more interesting thing is that there's already a step-down gearbox on the output. So is the motor turning at 3,100 rpm or the drill chuck?

Saw Guts Having started ... The saw is marginally more interesting. Motor is visually very similar. Looks like there might be a voltage regulator on the PCB. Also looks like the voltage controller has severly overheated at some point in the past :( But its till works fine. Must be a gear box in the pendulum chamber. As pushing the arm won't turn the motor I assume that it includes a worm gear.

To use a 240 V AC motor from a DC battery will be a challenge. Converters do exist, but those are mostly designed to operate heavy stuff (like your drill) from a car battery. I don't think any small robot will benefit from that setup. Who needs a 400 W of power in a DIY robot?

Consider recycling those motors, rather than reusing. There is magnets and enameled copper wire inside them.


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