Chainsaw dynometer build.
- Thread starter chadihman
- Start date
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parrisw
Tree Freak
Very cool.
chadihman
Addicted to ArboristSite
Look what this darn CAD does to a guy. Everybody thinks I'm crazy and they say your building a what??????????????
imagineero
Addicted to ArboristSite
Now all you need is another outlet hose from the pump, so you can run a log splitter off it too
Mastermind
Work Saw Specialist
I still want one. :msp_thumbup:
srcarr52
We can't stop here, this is bat country.
You're probably going to want a larger reservoir. You'll quickly overheat the hydraulic fluid in that little tank. Remember that you are basically converting all the power into heat. Mine is around 15 gallons and in two pulls with a kart it's up to 100 deg from 65.
chadihman
Addicted to ArboristSite
180 deg F is about the max you want to get the hyd oil too. I'm going to try this as is and if I need to add a trany cooler to it I will.
Mastermind
Work Saw Specialist
I've got a heater core from a semi if you need it.
CRE1992
ArboristSite Operative
Well since your in the mood for giving things away... How about a free port job for one of my saws ?
bikesandcars
ArboristSite Operative
I love the idea of a chainsaw dyno. I like the idea of the takeoff being post-sprocket so you can measure the HP "to the chain"... kind of like the difference between an engine dyno and a chassis dyno, very similar when you approximate transmission losses but a chassis dyno is the real measure of horsepower to the butt (and also to use in an essembled car).
If you're measuring porting impacts precision is more important than accuracy. What I'm saying is repeatability is more important than nailing the absolute "true" 3.54 hp or whatever HP saw you're measuring.
I'm not a big fan of hydraulic fluid and pumps for this application because extrapolating a pump curve backwards for varying HP doesn't seem like it will yield easily repeatable results... plus it sounds like it might get pricey. Hydraulic fluid will change viscosity with temperature, it will flow easier as it heats up, and to get the proper precision you will need to always run tests with the fluid at the same temp. This can be time consuming at minimum without some kind of chiller / heater for the fluid.
Here's another idea:
Friction disk: Utilize a brake hub assembly and caliper with a street brake pad (something with consistant friction with temp). Attach a pressure cylinder with a PSI gauge. Calibrate the dynamic torque with a variable rate torque wrench. when running increase pressure to the disk until you get the desired saw RPM. You can back-calculate the torque and rpm for HP based on the pressure. This is cheaper for what you want to do.
the also-rans:
I also thought of running a 12 volt generator with a DC motor attached to a large blade with "feathered" blades. You could measure current and voltage to the DC motor and thus calculate HP. Getting a 5 HP + dc motor however is out of budget.
You could do the same thing with a water / hydraulic pump arrangement. Since you are measuring voltage / amperage your repeatability is 100%.
If you're measuring porting impacts precision is more important than accuracy. What I'm saying is repeatability is more important than nailing the absolute "true" 3.54 hp or whatever HP saw you're measuring.
I'm not a big fan of hydraulic fluid and pumps for this application because extrapolating a pump curve backwards for varying HP doesn't seem like it will yield easily repeatable results... plus it sounds like it might get pricey. Hydraulic fluid will change viscosity with temperature, it will flow easier as it heats up, and to get the proper precision you will need to always run tests with the fluid at the same temp. This can be time consuming at minimum without some kind of chiller / heater for the fluid.
Here's another idea:
Friction disk: Utilize a brake hub assembly and caliper with a street brake pad (something with consistant friction with temp). Attach a pressure cylinder with a PSI gauge. Calibrate the dynamic torque with a variable rate torque wrench. when running increase pressure to the disk until you get the desired saw RPM. You can back-calculate the torque and rpm for HP based on the pressure. This is cheaper for what you want to do.
the also-rans:
I also thought of running a 12 volt generator with a DC motor attached to a large blade with "feathered" blades. You could measure current and voltage to the DC motor and thus calculate HP. Getting a 5 HP + dc motor however is out of budget.
You could do the same thing with a water / hydraulic pump arrangement. Since you are measuring voltage / amperage your repeatability is 100%.
srcarr52
We can't stop here, this is bat country.
I believe he is going to use a torque arm with a load cell so there will not be any need to back calculate HP from pump efficiency and account pumping losses. Temperature of the hydro fluid will not matter for the measurement, just for longevity of the fluid.
It has been a while since I have looked at this, but if you know the moment of inertia for the flywheel, all you really need is a measurement of rpm indexed to time. Is that correct?
dieselfitter
ArboristSite Guru
Chad, there was talk of using a proximity tach for monitoring the rpms. If you are wanting do instead used a hall effect sensor like these:
Digital Speed Sensors
I have a few of these lying around somewhere and can donate one to the cause.
Downside, it requires external voltage source.
Upside, it provides a digital signal that doesn't require conversion from analog. With the right connection and software, you can hook this right to the laptop. I'm hoping someone smarter than me can help you with that.
I think I still have some new transmission oil coolers lying around and can donate one to the cause.
I have a new pyrometer if you are interested. Sorry, I can't be giving this away, I have too much money into it. Picture attached, $125, Stewart and Warner N.O.S made in USA, good stuff! DF
View attachment 292966View attachment 292967View attachment 292966View attachment 292967
Digital Speed Sensors
I have a few of these lying around somewhere and can donate one to the cause.
Downside, it requires external voltage source.
Upside, it provides a digital signal that doesn't require conversion from analog. With the right connection and software, you can hook this right to the laptop. I'm hoping someone smarter than me can help you with that.
I think I still have some new transmission oil coolers lying around and can donate one to the cause.
I have a new pyrometer if you are interested. Sorry, I can't be giving this away, I have too much money into it. Picture attached, $125, Stewart and Warner N.O.S made in USA, good stuff! DF
View attachment 292966View attachment 292967View attachment 292966View attachment 292967
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bikesandcars
ArboristSite Operative
Sorry, I guess I tried to catch up too quickly. I missed the torque-arm and load cell key points
I still like my auto-brake idea for simplicity over hydraulic pumps and the like
Mastermind
Work Saw Specialist
Well since your in the mood for giving things away... How about a free port job for one of my saws ?
Trade you that 361 for a woods port on the 261.
srcarr52
We can't stop here, this is bat country.
Yes, that is why they'll give you the hardware/software for only $800.
Sorry, I guess I tried to catch up too quickly. I missed the torque-arm and load cell key points
I still like my auto-brake idea for simplicity over hydraulic pumps and the like
I have a hydro brake kart dyno that I hope to get converted to a torque arm with data aqc this year.
FYI. Friction brakes are extremely temperature dependent not to mention would heat up very quickly for a dyno. It would be very difficult to keep the engine at a stable RPM or a small enough rate of change to get decent readings.
bikesandcars
ArboristSite Operative
How much HP does a Kart make? I guess that's the key criteria for energy dissipation.
I was just offering a cheaper solution that fits easily on a bench and because I like the mental gymnastics.
Auto brakes are somewhat temperature dependant, racing pads more-so. If you go with a street ceramic pad the dynamic friction is generally very consistant with temperature.
A car weighs 3000 lbs and decelerates from 60 in approximately 5 seconds. The front brakes do 2/3rds of the work, therefore each brake does 1/3 of the total work required.
Decelerating 3000 lbs from 60 mph to 0 mph in 5 seconds requires 240 hp of work (using a quick internet calculator). 1/3 of 240 hp = 80 hp.
A non-competition 80cc chainsaw might produce around 6 hp for an example.
That means that a single average front brake rotor can dissipate 10 x the energy that a chainsaw will generate in the same time (5 seconds), or theoretically could dissipate that energy for a much longer time. You could rig it so your right hand holds the chainsaw and your left hand holds a lever that works the brake, so you could have complete control.
I was just offering a cheaper solution that fits easily on a bench and because I like the mental gymnastics.
Auto brakes are somewhat temperature dependant, racing pads more-so. If you go with a street ceramic pad the dynamic friction is generally very consistant with temperature.
A car weighs 3000 lbs and decelerates from 60 in approximately 5 seconds. The front brakes do 2/3rds of the work, therefore each brake does 1/3 of the total work required.
Decelerating 3000 lbs from 60 mph to 0 mph in 5 seconds requires 240 hp of work (using a quick internet calculator). 1/3 of 240 hp = 80 hp.
A non-competition 80cc chainsaw might produce around 6 hp for an example.
That means that a single average front brake rotor can dissipate 10 x the energy that a chainsaw will generate in the same time (5 seconds), or theoretically could dissipate that energy for a much longer time. You could rig it so your right hand holds the chainsaw and your left hand holds a lever that works the brake, so you could have complete control.
LegDeLimber
Addicted to ArboristSite
I'm still just thinking low budget here
but would a good brand of meat thermometer
if you could (ideally) get it hung so that it's in the stream of the return oil flow
be of any help?
==
I've been knocked offline for a few days, good to see your work progressing nicely!
but would a good brand of meat thermometer
if you could (ideally) get it hung so that it's in the stream of the return oil flow
be of any help?
==
I've been knocked offline for a few days, good to see your work progressing nicely!
chadihman
Addicted to ArboristSite
This one will be for sale if it works as planned. You helped me out with my getting started in porting so you get the first shot.
