Chainsaw Flashlight (gas Engine Powered Spotlight)




About: Dad and hubby, good food enthusiast, solar energy, boating, making stuff, melting stuff, and raising chickens.

I've been wanting to try this for a while as crazy as it sounds; make a mini electric generator with a small engine and a treadmill motor, add this to some car headlights and you get one very loud flashlight/spotlight. 

An electric motor is basically a generator and an electric generator is basically an electric motor. The chainsaw provides the power to spin the motor and booyah....electricity. I'm sure all kinds of electrically proficient peeps will shake their heads at the methods here, but it's all just fun, nothing serious. 

(I want to add that I squeezed this project out to meet the flashlight contest deadline; it still needs a voltage regulator, a protective shield for the chain and sprockets, plus some adjustments and fancy paint work.)
Final adjustments to this machine, a voltage regulator is not needed if the saw throttle can be incrementally adjusted with a hose clamp. Hook up a multimeter and set the throttle before plugging in the light. Also the gearing in this instructable is way too high, the DC motor sprocket needs to be much larger to slow it down. I can hand turn this DC motor and get 2 to 3 volts, so the chainsaw should barely be running above idle to get the right voltage. This project is a little dramatic; maybe next time I'll use a lawnmower engine ;).

Here we go:

1 old chainsaw
1 treadmill motor (DC permanent magnet motor)
1 one-piece 12 volt car headlight bulb
odds and ends tubing, wires, switches (see detailed steps)
bicycle spockets
bicycle chain
motorcycle voltage regulator
scrap wood and screws

welder or someone who can weld a sprocket to a chainsaw clutch and treadmill motor flywheel.

(Extra: With a few alterations, this project can be made into a mini generator or a go kart.)
Warning, this can be dangerous. I'm not liable for any injuries or whatnot incurred using the shown techniques. At your own risk and stuff. 

Step 1: Remove Sprockets From Bicycle and Line Up Best Fit

I needed a bike sprocket on the chainsaw and on the electric motor. An old bike somebody threw away worked well for the parts. I used the smallest outer sprocket on the hub to attach to the saw and the larger set behind it for the DC motor. Don't ask me how I got this apart, I'm not a bike mechanic; and all that is left of the wheel is a pile of spokes, ball bearings, and cut up pieces of the axle hub thing. ;)

Step 2: Weld the Sprockets

Most people would probably say "ahh, nevermind" at this step, but it's the only welding part. This is important to get straight an centered. I tried not to over-weld and warp things from too much heat. Then I cleaned up the weld splatter with a die grinder.
Also once everything was aligned, I put a spot weld on the treadmill motor shaft to keep the flywheel from unscrewing, it's not the usual lefty loosey, it is righty loosey here.

Step 3: Design and Configure the Machine

l lined things up for a best fit, brackets, handles, and lights will all be different with different models of chainsaws and stuff. A little creativity is needed here. I used metal plumbing straps, screws, scrap plywood, and some odds and ends here.

I tried several configurations until it seemed to look like it would work.

Step 4: Add Some Wood Framing

Wood screws and some scrap wood work well for attaching accessories to the saw platform. Like I said earlier, different engine models and motors will need different techniques to patch together. Not many people probably have a 1960's era chainsaw like the one used in this project. Look at how plumbing strap and wood screws are used in the pictures.

Step 5: Add Chain and Make Final Adjustments

I picked up one of those bicycle chain breaker tools and shortened the chain to what I needed.
I made sure the bicycle chain was lined up straight and snug, not too tight or loose.

Step 6: Mount the Light and Regulator

In the video I didn't use a voltage regulator and burned out the bulb . I'm going to get a better bulb/spotlight next round and an old motorcycle voltage regulator. If the chainsaw engine is not revved up too much, one could get by without it, but not for long. The negative (black) and positive (red) wires from the electric motor are connected directly to the bulb here; ideally a voltage regulator would be in between. I had one laying around the garage somewhere; when I find it, I'll repost the pictures and video.

Step 7: Video and Extra Notes

This video shows the first test starts and the light blowing out.
Also, I would use a pulley and belt next time instead of the bicycle chain; it's so hard to get it lined up and it likes to pop off and roll across the yard.

No chainsaws were harmed in the making of this video or project. The vintage 1960s era Homelite is still reversable. Most would think Homelite is a low end brand, but it was a great machine back then. It had been setting for decades before I added some fresh gas and fired it up on the third pull. 

Runner Up in the
Flashlight Contest



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    130 Discussions


    1 year ago

    This is the best thing I have ever seen on instructables


    8 years ago on Step 7

    Leave the bar and chain saw on it, then you could saw in the dark! ok, probably still a bad idea..

    2 replies

    Reply 8 years ago on Introduction

    "saw in the dark"! And the award for best pun goes to wheredgo!! :] In fact you could see/saw* in the dark... Ooops, best pun goes to me. Love the idea of the chainsaw light robbtoberfest: I'll have to try it ... "come here little chainsaw ... where are you boy? ... come into this nice workshop ..." *Or I saw where I could see to saw a seesaw in the dark. OMG!!!: robbtoberfest built a SeeSaw!! [tm]


    8 years ago on Introduction

    this would be perfect for a horror film just the effect of building it then moving around a dark house with the pulsing light and the posibility of the motor cutting out (for teh film of course) to plunge teh character in darkness only for a shocking reveal make this a perfect prop and effect well done

    1 reply

    6 years ago on Step 7

    +1 vs. Zombies, upgrade to HID for +2 vs. Vampires.


    Reply 6 years ago on Introduction

    if you want to build a gen set based upon a car alternator your best (and least expensive) is a single wire Chevrolet. The older ones run about 63 amps. They can be rebuilt to produce higher amps but you may run into problems with over heating. This can be avoided by using an alternator from a mid to late 1980s 80 amp alt and have it rebuilt to a higher (about 120 I think) rating. Because it is physically larger it does not have the issues with the cooling. I learned this from the owner of the local automotive starter/generator/alternator rebuild shop. good luck!!


    7 years ago on Introduction

    See the problem with this is that most of the time when I use a flashlight its at night and my neighbors would get pretty mad if I fired up an old chainsaw engine every time I needed to see.


    8 years ago on Introduction

    May I suggest that you replace the permeant magnet motor with a internally regulated car alternator. That way, you will be putting out 13v no matter what. The only problem is a small amount of power is required to energize the fields.
    My 2c

    1 reply

    Reply 8 years ago on Introduction

    Also also, at a constant 13Vdc hi intensity chip LEDs become an option (an expensive one though). that would be A LOT of lumens!!


    8 years ago on Introduction

    Only in America does one need gasoline to see in the dark. Awesome instructable!


    8 years ago on Step 7

    That is one BA flashlight, i want to bring on a boyscout campout. "WOULD YOU TURN THAT OFF?!?!?" "No, we need it to play magic"