Chainsaw Dyno bring saws to there knees. Build from start to end with video

[spacemule]

See post # 110 ........... there was a loup "POP" when my head was pulled from my arse, and everything was clearer after the Molson XXX wore off. Nice examples !

lol. I missed that.

 

[Team FAST]

Interesting

A couple of things:

1. Congrats on the build and the effort. It is really cool!

I think its important for folks to realize that the horsepower numbers being reported from this are fairly meaningless, within the context of "that saw should be producing XX.X hp" This in no way is meant to disparage this most excellent device you made!

Your horsepower numbers are derived - calculated from a scale reading, a lever arm length, and an observed RPM value. The rotational assemly of the dyno is being driven indirectly from the MUT (motor under test) by a chain drive system. There are bearings on the shaft. Many factors lie between that little combustion chamber (the seed of the POWER) and the readout on your scale.

So you inherently (as all dynos do) have lots of error sources:

- scale inaccuracies (probably as much as 5%)
- torque arm length uncertainty (knowing *exactly* how long it is)
- rpm measurement uncertainty (the meter will have some error associated with it)
- frictional losses in shaft bearings (probably small)
- losses due to chaindrive system (high) <----interesting test.....try just messing with lube oils on your chain drive system as you are running the dyno and watch the toruqe readings change

Note that the hydraulics side as you implemented it is simply for load absorption. The pump efficiencies, performance, etc, have zero bearing on errors associated with the torque reading, only on the absolute capacity of the dyno, and the relationship between the load absorbtion input (your flow valve) and the torque reading. This would only become significant if you chose to automate your dyno with automatic load controls (like a modern Superflow setup). In order words the absorption side has nothing to do with accuracy of torque readings, as long as its stable.

That's just the mechanical parts. The other thing you have to be really aware of....even when trying to do relative measurements, are things like ambient conditions (air temp, humidity, density altitude, etc) as well as the temperature of the saw engine. On a two stroke engine, crankcase temperature has a HUGE impact on engine volumetric efficiency, and effective air fuel ratio....therefore horspower...

All of these factors have to be taken into account when reporting SAE Corrected horsepower numbers. SAE has test procedures and methodlogies to specifically address dyno testing. Not relevant for what you are doing here, of course.

Just some things to think about!

I'm slowly working on my own dyno....eddy current based system using an automotive alternator as the load control and a bank of resistors for load absorbtion.

 

[PogoInTheWoods]

Excellent!!!

 

[chadihman]

Great job putting talk into reality, then publishing your reality for others!

That's 2 steps more than most take and 1 more than many people do once they put the work in. I think it looks great

I read through this entire post and I can't find the answer to a simple question I had.. where on earth do you get a 24 tooth chainsaw sprocket? What did you use for chain? (grind the cutters off?)

I found the 24 tooth sprocket in a company from Washington state. I found a cutterless chain online

 

[barneyrb]

I found the 24 tooth sprocket in a company from Washington state. I found a cutterless chain online

Wonder if my wild thing would pull that....hhhmmmmmmmm

 

[Scooterbum]

Ignoring all the naysayers, nitpickers and brainiacks. I love it when someone starts out to make something from scratch and finishes it and it works exactly as it's intended purpose. To measure gains and losses when modding a chainsaw.

You should maybe look into manufacturing it. Small niche market, but it's there.Could be differrent versions. Chainsaws aren't the only 2-smokes being modded.

Great work !!!

 

[chadihman]

Here is the company I got the 24 tooth sprocket from Sprocket Applications

 

[ozflea]

Here is the company I got the 24 tooth sprocket from Sprocket Applications

Thanks ol mate i'll go chase one up .............

 

[chadihman]

This is the cutterless chain Bailey's - Oregon 72W Cutterless Chainsaw Chain

 

[peacmar]

One thing I haven't noticed mentioned that would account for the inaccuracy of the reading, friction and inertia aside, is the increase in temperature of the hydraulic fluid. I've built a few small engine dyno in the past and the simplest is driving a positive displacement pump. Hydraulic pumps are simple and cheap to come by and can stop a very large load. I used have a 400 HP rig that used a 50 HP hydraulic pump out of an old combine. There was only one source of measurement in power and that was a pressure/temp gauge. As the pressure went up rolling resistance was placed on the engine and by calculating the temperature increase of the fluid at a given rpm one could determine work done and torque applied. I cannot for the life of me find the old files I had with the formulas in a spread sheet but know I found them online very easily.

So if you take the fluid temp increase, along with the friction of the chain, slippage in the clutch, resistance of a viscous fluid through the pump, and bearing friction all into account. You should have a very accurate setup. As someone who has spent the last ten years developing import race engines and countless hours of dyno work I must say nice work!

 

[chadihman]

Not sure if I can ask this but here goes. Would anybody be interested in a dyno if the cost was $1500. Maybe I could make them cheaper on the next build. I'm just trying to figure out if this would be worth manufacturing.

 

[67L36Driver]

Excellent grass roots approach on your dyno build. Simple and made with readily available parts. Good job.



Only thing I can offer is to keep an eye on the length of run under full load. No telling what duty cycle (on/off) chainsaws are designed for. Fellas running mills could maybe give us a clue.

Watch out for powerhead melt down.

Carl.

 

[Gologit]

Not sure if I can ask this but here goes. Would anybody be interested in a dyno if the cost was $1500. Maybe I could make them cheaper on the next build. I'm just trying to figure out if this would be worth manufacturing.

You're still in the development stage and you're not actually advertising anything for sale so we'll let you run with this a little. Call it market research or something.

If you start building them and you're advertising and selling them on AS you'll need to get a sponsorship.

Good job, by the way. And good luck.

 

[booger1286]

Awesome build! Somebody might have already said this but, looks like it could use another pivot point right above the base on the scales. Especially since the arm is off center.
That should make a difference in your readings for the better.

 

[nelson727]

First saw this dyno thread a few days ago. Man my hat is off to you chadihman that is some beautiful work. I just keep my saws running for the job so wouldn’t pay $1500 for a dyno. If I lived next door to you I’m sure I would be asking you to build this and that for me and soon be up to 15K. Amazing!

 

[peacmar]

I've been thinking about this thing since I first read it and have an idea for a way to verify the readings.

Use an electric motor you have laying around, any motor of any size, and use a volt meter and amp meter to record the wattage used when loading the motor to its full potential. Wattage can be easily converted to HP with a simple calculation. Compare your wattage input to your dynos recorded power absorbtion and you will then know your correction factor. Try this when your fluid is cold and hot and you may be able to interpolate and graph a correction chart based in fluid temperature. I would think it would be a linear function. Then forget the rest and keep it simple. As most who have worked with a dyno know, it is about proving repeatable results and recording changes, not the final numbers. So if you start out with a baseline reading of a saw then record power improvements after each mod and can repeat the results you would therefore have a scientifically proven method of data acquisition.


An individual could also use a spare saw as a "mule engine" one that is never touch or changed. A mule engine is used to make the first couple of runs each time a dyni is used. Those runs are compared to the previous mule engine runs, and a correction factor is derived from the difference in results. Allowing an individual to compensate for changes in testing conditions that may have occurred over a couple weeks or months between tests.

 

[chadihman]

I've been thinking about this thing since I first read it and have an idea for a way to verify the readings.

Use an electric motor you have laying around, any motor of any size, and use a volt meter and amp meter to record the wattage used when loading the motor to its full potential. Wattage can be easily converted to HP with a simple calculation. Compare your wattage input to your dynos recorded power absorbtion and you will then know your correction factor. Try this when your fluid is cold and hot and you may be able to interpolate and graph a correction chart based in fluid temperature. I would think it would be a linear function. Then forget the rest and keep it simple. As most who have worked with a dyno know, it is about proving repeatable results and recording changes, not the final numbers. So if you start out with a baseline reading of a saw then record power improvements after each mod and can repeat the results you would therefore have a scientifically proven method of data acquisition.


An individual could also use a spare saw as a "mule engine" one that is never touch or changed. A mule engine is used to make the first couple of runs each time a dyni is used. Those runs are compared to the previous mule engine runs, and a correction factor is derived from the difference in results. Allowing an individual to compensate for changes in testing conditions that may have occurred over a couple weeks or months between tests.

Well I'm now working on getting it dialed in. I got some vibration dampening pads for the scales to sit on and a new scales on the way to compare the two. I'm reworking the hoses for less drag. I'm using my stock 461 as the mule.

 

[LegDeLimber]

My gut take on this is...
It'll be a darn handy thing to have in the shop for all the reasons mentioned
around tuning motors and keeping notes on 'em.
hmmm, how many adapters can you rig for checking the [local ?] lawn mower racer's engines etc ??

2nd: I'd wager this thing will be a big hit at the first few GTG's
*IF* you have the opportunity/time etc to carry it around...

I'd love to make my first trip to a GTG and see the first "dyno races"
...could make for some interesting "tuning clinics" and so on.

Ahh I have other ideas,
but as always more ideas will lead to more new variables to have differing opinions on.

 

[chadihman]

My gut take on this is...
It'll be a darn handy thing to have in the shop for all the reasons mentioned
around tuning motors and keeping notes on 'em.
hmmm, how many adapters can you rig for checking the [local ?] lawn mower racer's engines etc ??

2nd: I'd wager this thing will be a big hit at the first few GTG's
*IF* you have the opportunity/time etc to carry it around...

I'd love to make my first trip to a GTG and see the first "dyno races"
...could make for some interesting "tuning clinics" and so on.

Ahh I have other ideas,
but as always more ideas will lead to more new variables to have differing opinions on.

I'd haul this to a gtg if one were close by. I would let anyone run and tune there saws on it.

 

[LegDeLimber]

Chadiham, PM in your box if I didn't goof up sending it.
sorta bouncing from one task to others in prep for knee repairs