Chainsaw dynometer build.
- Thread starter chadihman
- Start date
Help Support Arborist Forum:
Chris-PA
Where the Wild Things Are
Yeah, with that you can find energy at each rpm. If you know the time between the energy readings you can calculate power. So I would think that with a plot of rpm vs. time you'd have it all mapped out.
But that is a dynamic test - you cannot hold it at an rpm, you can only sweep it over the range - and I wonder what difference that makes? You couldn't really do certain types of analysis, like measuring fuel consumption or fuel mixture. And real-time tuning wouldn't work, you'd have to do separate runs and compare.
Thanks, that explains it!
Last edited:
There are advantages to both types of dyno. If I were building a cookie cutter for race use, even if it only raced at local GTGs, I'd go with the flywheel type for at least some of the testing. On the flip side my saws cut and sometimes mill big logs, they run under heavy load for long periods of time and if the engine is going to burn up during testing it is really going to fail quickly when I try to get some work out of it.
Another note on the flywheel dyno is that it has to be sized to the output range of the engine. Some guys I know were trying to get their trucks tested on a flywheel type dyno that was sized for muscle cars. The big built up diesels were maxing out the flywheel long before they were using up the power that the diesels could put out.Basically they were using a dyno that was too small for the power range they are putting out. There is of course a huge debate about that going on in gear head forums all over the internet, but to my thinking the physics of it are real, there is a need for the correct size. Same as not trying to pull a loaded log trailer up a hill with a Prius.
I think the two basic types of dyno are both valid, but certain build objectives are measured better by one type over the other. Someone building a top fuel dragster wants a differnent animal under the hood than the guy running a truck in Dakar.
Mr. HE
Another note on the flywheel dyno is that it has to be sized to the output range of the engine. Some guys I know were trying to get their trucks tested on a flywheel type dyno that was sized for muscle cars. The big built up diesels were maxing out the flywheel long before they were using up the power that the diesels could put out.Basically they were using a dyno that was too small for the power range they are putting out. There is of course a huge debate about that going on in gear head forums all over the internet, but to my thinking the physics of it are real, there is a need for the correct size. Same as not trying to pull a loaded log trailer up a hill with a Prius.
I think the two basic types of dyno are both valid, but certain build objectives are measured better by one type over the other. Someone building a top fuel dragster wants a differnent animal under the hood than the guy running a truck in Dakar.
Mr. HE
Chris-PA
Where the Wild Things Are
I agree. A chainsaw is actually more of a steady speed device, unlike the race carts engines described in Blair's paper. You hold it WOT when it is cutting, and only the load causes speed variation.There are advantages to both types of dyno. If I were building a cookie cutter for race use, even if it only raced at local GTGs, I'd go with the flywheel type for at least some of the testing. On the flip side my saws cut and sometimes mill big logs, they run under heavy load for long periods of time and if the engine is going to burn up during testing it is really going to fail quickly when I try to get some work out of it.
Another note on the flywheel dyno is that it has to be sized to the output range of the engine. Some guys I know were trying to get their trucks tested on a flywheel type dyno that was sized for muscle cars. The big built up diesels were maxing out the flywheel long before they were using up the power that the diesels could put out.Basically they were using a dyno that was too small for the power range they are putting out. There is of course a huge debate about that going on in gear head forums all over the internet, but to my thinking the physics of it are real, there is a need for the correct size. Same as not trying to pull a loaded log trailer up a hill with a Prius.
I think the two basic types of dyno are both valid, but certain build objectives are measured better by one type over the other. Someone building a top fuel dragster wants a differnent animal under the hood than the guy running a truck in Dakar.
Mr. HE
Also, with a flywheel dyno you would need to account for the moment of inertia of the saw's own flywheel, or make sure the dyno flywheel is much more massive. For a braking type dyno it doesn't matter.
I guess they're just different.
Hhhmmmm....sound like you guys have done it, been there and all that.
Inertial will give you all you want and for the least investment in dollars. The software takes care of pretty much everything you can think of and it is put up real time on the screen of your comp. The parasitic drag is measured by the time it takes the wheel to come to a stop. Once the software has had that to play with, everything comes out minus the drag, so you know what you are making. Or you can set it up to leave it in. Up to you.
Rather than guess about the system you can go to the website and read all the good things the package will do for you.
Inertial will give you all you want and for the least investment in dollars. The software takes care of pretty much everything you can think of and it is put up real time on the screen of your comp. The parasitic drag is measured by the time it takes the wheel to come to a stop. Once the software has had that to play with, everything comes out minus the drag, so you know what you are making. Or you can set it up to leave it in. Up to you.
Rather than guess about the system you can go to the website and read all the good things the package will do for you.
Last edited:
Chris-PA
Where the Wild Things Are
No need to get your back up, no one was slighting either system. I've certainly not been there or done it, but it is interesting to think about and discuss the way the two approaches work and what they can tell you. They are not the same, and they are not equivalent. They each have advantages and disadvantages - the flywheel approach would be much simpler mechanically.
Mastermind
Work Saw Specialist
CRE1992
ArboristSite Operative
Trade you that 361 for a woods port on the 261.
Why do I feel like that trade would be squed in your favor? Lol. :msp_sneaky:
Don't worry one day I'll send you a saw to port!
bikesandcars
ArboristSite Operative
I think the flywheel approach for an intertial dyno has great merit for measuring accelerating engines (like auto, motorcycle, etc). Also very useful for chainsaw raw HP with RPM ( and torque) readings and certainly if you just wanted to mount a small flywheel on your bench with the tach and a small computer that would be easiest. The computer setup also lends itself to nice graphs for customers. The downside is you need the computer to make it work.
I think a brake dyno has certain advantages if you want to go simple because you don't really need a computer or software at all. Set the brake to bring chainsaw tach down to a cut rpm, say 13,500 rpm, read the UPS scale you have on the side of your lever arm... calculate torque, calculate HP, the rest is just maths . For just getting baseline measurements this may be good enough (though not as nice as a graph with rpm).
A brake dyno also has a nice advantage of being able to tune saws in the "cut" without making so many cookies and you can also break them in.
just throwin it out there for discussion, any of these ways hold merrit IMO
I think a brake dyno has certain advantages if you want to go simple because you don't really need a computer or software at all. Set the brake to bring chainsaw tach down to a cut rpm, say 13,500 rpm, read the UPS scale you have on the side of your lever arm... calculate torque, calculate HP, the rest is just maths
. For just getting baseline measurements this may be good enough (though not as nice as a graph with rpm). A brake dyno also has a nice advantage of being able to tune saws in the "cut" without making so many cookies and you can also break them in.
just throwin it out there for discussion, any of these ways hold merrit IMO
chadihman
Addicted to ArboristSite
I started a new thread but I thought it might be a good Idea to finish this with a video of the finished product. [video=youtube_share;VGpxVzkYU70]http://youtu.be/VGpxVzkYU70[/video]
