Introduction: Chainsaw Flashlight (gas Engine Powered Spotlight)

Picture of Chainsaw Flashlight (gas Engine Powered Spotlight)

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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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. 


masoon (author)2017-11-28

This is the best thing I have ever seen on instructables

devicemodder (author)2015-03-15


randomray (author)2014-10-12

Uhmmm, I love the insanity of the project.

wheredgo (author)2010-08-12

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

dudes (author)wheredgo2014-03-28

that would be AWSOME!!!!!!!

finton (author)wheredgo2010-08-13

"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] (author)2013-07-22

This is awesome!

jlyvers743 (author)2013-04-05

This is the ultimate man-cave lamp!! So awesome!!

TechDante (author)2010-08-18

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

r_harris2 (author)TechDante2013-04-04

Yeah, or I was thinking haunted house, live action. :-)

bennelson (author)2013-01-15

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

camping crazy (author)2012-12-03

I just love over kill! Nice project although isnt it a bit noisy

weldor (author)2012-06-28

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!!

zilcho (author)2011-11-11

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.

super tubes (author)2011-08-26

vrom vrom, im goin to blind you!

lukeyj15 (author)2011-05-04

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

adelfino06 (author)lukeyj152011-06-16

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

SirStokes (author)2011-03-16

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

Terivia (author)2010-08-21

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"

bombmaker2 (author)Terivia2011-02-18

I was thinking:

"NO!!!! I got to a good part in this book!"

quadracer (author)2010-11-25

You can adjust the carb so it idles high enuff to engage the clutch.

2 stroke (author)2010-10-20

yo man is that an princess auto welder by the looks of the gun and ground clamp looks like the flux wire welder they have if so i have their 70 amp stick welder

nedfunnell (author)2010-09-24

Awesome build!

bart245 (author)2010-08-21

That little flashlight project you built there is awesome! Great job!

wizworm (author)2010-08-20

You need to take that to Burning Man, that would be a hoot

SwaggeringPagan (author)2010-08-18

Who cares about practicality, gimme internal combustion! Very cool survivalist/dieselpunk rig.....

treehouse24 (author)2010-08-13

to the Creator this is old news, i mean as a bush man i was hunting one fall day when i left my lights on when i walked away from my truck returning 6 hours later it would not start as the batteries were dead , sitting there i thought it is a 30 mile walk or better yet charge the battery, i used my small chainsaw to charge the battery, taking off the belt from the alternator and the chain and bar from the saw i put the belt over the clutch , making sure the direction of travel was the same , i started the saw hand pulled the belt tight and for a few minutes turned the alternator to charge up, replaced everything and started the truck , when home with no blisters , here is your next how to instruct able, take care thanks, gord, as for the light not practical , yet make it for loggers in the dark led to run off the handlebar heater ,to light you work area, or even cooler two leaser lights triangulated to set at 49.6 feet to make one dot ( saving running a tape to measure the log and cut

Lorellai (author)treehouse242010-08-15

Many things on here are 'old news' but people still enjoy documenting their creations or instructing on their own particular way of doing things. Be nice, not jealous!

treehouse24 (author)Lorellai2010-08-16

It was not my intention to make a negative comment on someone else's project , it was my intention to give him an idea to up his project to use of an application that probably has never before been demonstrated,such as the leaser lights triangulated to set a distance, but to others that may be old news as well as it was used on ww2 bombers using two lights to to set distance as well,so i am sorry if i offended anyone,

Lorellai (author)treehouse242010-08-17

I apologise for being so tetchy!

Good ideas. I really like the laser light idea added to this to measure distance.

robbtoberfest (author)2010-08-16

130 VDC and 6700 RPM, the other one I have is 90 VDC but no RPM listed. Next time building a system like this I'd probably use a direct drive instead of clutch and put a hose clamp throttle adjustment on the handle. I'm thinking of making a light duty welder with this, but I don't know what to do quite yet.

AAAdrian san (author)2010-08-16

thats kool maybe me and my twin juan can do that one day

memano (author)AAAdrian san2010-08-16


memano (author)2010-08-16

cool i have a neighbor that did that to a bike

jamilks (author)2010-08-15

Very Creative! Good for you! Should point out that one of the conditions is that you have a permanent magnet motor...dil-willy, the alternator is kinda a good idea except that you need some incoming power to initially set up the magnetic field in the alternator coils....That's why if you have a TOTALLY dead battery, starting a car with jumper cables may not always need to get some sort of minor charge in the battery.

mouse23 (author)2010-08-12

Couldn't a n automotive alternator have been used? They have a regulator module on it already. And there are plenty of them around.

robbtoberfest (author)mouse232010-08-12

Could be used, but an alternator needs a battery to power the electromagnet inside it.

mouse23 (author)robbtoberfest2010-08-15

To clear up some mystery. From : "It seems like we have a catch-22 situation here: the generator cannot output a voltage until its field winding is energized, but its field winding will not be energized until the generator (armature) outputs some voltage. How can this generator ever begin to output voltage, given this predicament?" file 00812 The answer is "Remanent Magtetism" which creates a little voltage which is fed to the field winding which then will strengthen the magnetic field, creating more voltage etc. Old timers (like me)may know that newly installed "generators" in old cars may NOT work right out of the box. They have to be momentary magnetized by applying 12V to the terminal. This will give them that remanent magtetism. Some new generators may come with remanent magnetisms of wrong polarity which creates all kinds of fun. Therefore one should always polarize one of those generators after installation.

havocgtr (author)robbtoberfest2010-08-13

"an alternator needs a battery to power the electromagnet inside it" Really??? I only ask because i have driven a few cars on just the power of the altenator (no battery installed was removed after starting the engine) (it was one of those hey yall watch this moments)

Funk_D (author)havocgtr2010-08-14

Regulator in the alternator, not the battery. lol.

Funk_D (author)havocgtr2010-08-14

I've wanted to make a generator from a weed-eater and an alternator for the longest time, and all my research says that a battery needs to be used for an alternator to work. If you don't, it supposedly can burn out that regulator that's inside the battery. I'd say if you ran a car on just power from the alternator then it might have been a model that didn't have an internal regulator, as some older ones apparently don't have them. Also on older cars, you don't need the electric system for them to run, just to use lights/radio/etc. Also, Rob, thank you for this idea! Like I said I've wanted to build something like this but never thought to just weld bike sprockets to the shafts and use a chain! I was thinking about some kinda direct-drive thing. I want to make a small generator for camping trips and this helps a lot!

robbtoberfest (author)havocgtr2010-08-14

Most alternators need a battery, there are some that don't.

i have a chainsaw the produce extra voltage to heat a handlebar enough to charge a an alternator

robbtoberfest (author)2010-08-14

Thanks for the tips. What if I used an old dead motorcycle battery, would that level the voltage?

mysss (author)2010-08-13

I feel I should note that this should be made of heavy guage metal, not like plastic or something*. ;-) Props on a really crazy idea, imho :-P *bike chains can cut/seriously maim you when they break WHILE ON A BIKE. keep this in mind.

3366carlos (author)2010-08-13

Very ingenious, dunno if the bike cogs can handle high RPMs for very long. They may disintegrate eventually.

hot-fresh-rider (author)2010-08-13

Cletus what yo doin with yo sister? Nothing Ma! We just playin! :o)

nubie (author)2010-08-13

Very cool, possible variations include: Weed whacker motor instead. Use a tiny alternator to get voltage regulation. Check out mini alternators for racing applications, they are usually original equipment on small foreign cars in the junkyard. Use a very bright bulb, or a pair of them with the high and low beams on.

About This Instructable




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