Chainsaw dynometer build.

[chadihman]

My dyno is currently measuring pressure and flow to calculate HP. Look up Prototype dynos.

An accurate flow meter that you could read in small increments would be more expensive than a load cell or scales that will read accurately.

 

[srcarr52]

An accurate flow meter that you could read in small increments would be more expensive than a load cell or scales that will read accurately.

I know... it's just the way it came and it works for now. I will mount a load cell on the pump soon, before kart season kicks off again.

 

[chadihman]

Keeping the rpms down on the dyne would save heat, may I suggest a gear box from a small old dump, they are compact and should get you to the reduction you need.

I agree with the rpm's and heat but dont think the gearbox is a good idea. Gearboxes,chains, belts,shafts and exrta bearings all cause extra drag or resistance. We have a large pto dyno at work for testing 400 hp tractors. The horsepower is lower than the egine hp beacause the tractor has so many bearings,gears and shafts to get the power from the engine to the pto shaft on the rear of the tractor. A truck or car has much more hp tested at the flywheel vs the wheels.

 

[drkptt]

Effectively all the shaft power of the engine is going into heating the oil. Doesn't matter how small the pump is, what the flowrate is, or what speed the pump turns. 3 gallons is not a large reservoir, it's going to get hot. Running a 3 hp saw continuously is the same as putting a 2300 Watt heater in the oil tank.

 

[dl5205]

I believe either Walkers or Madsens has a saw dyno. I also seem to remember another Arboristsite member (TimberWolf?) had built a saw dyno.

If I were setting out to build a Saw-Sized Dyno, I would look hard into what is already out there, and try to use/improve on designs that already work.

 

[Simonizer]

1 ft/lb on a 1 ft bar would read 1 lb....... 1ft/lb on a 5 ft bar would read 0.2 lb. Your thinking backwards

That is why I said multiply it by 5. (0.2 x 5 =1) Who is thinking backwards again? BTW it is Ft*lb not Ft/lb. It is the product of the two units not the quotient. Good day sir.

 

[chadihman]

Effectively all the shaft power of the engine is going into heating the oil. Doesn't matter how small the pump is, what the flowrate is, or what speed the pump turns. 3 gallons is not a large reservoir, it's going to get hot. Running a 3 hp saw continuously is the same as putting a 2300 Watt heater in the oil tank.

I guess I'll find out. I built a power unit for work that has a 10 gpm pump running at 2500 psi sometimes for 5 min. It has a 8 gal tank with a thermometer in it. The temp never goes past 150 deg. It's ok for hyd oil to get 100 deg hotter than your air temp. 75 deg day and 175 deg oil.

 

[chadihman]

That is why I said multiply it by 5. (0.2 x 5 =1) Who is thinking backwards again? BTW it is Ft*lb not Ft/lb. It is the product of the two units not the quotient. Good day sir.

Sorry about that. I went back and read your post again. I like your thinking. Please don't hate me for being stupid.

 

[Simonizer]

Sorry about that. I went back and read your post again. I like your thinking. Please don't hate me for being stupid.

I like your thinking too bro. Don't hate me for being an engineer. Cheers,

 

[Walt41]

I agree with the rpm's and heat but dont think the gearbox is a good idea. Gearboxes,chains, belts,shafts and exrta bearings all cause extra drag or resistance. We have a large pto dyno at work for testing 400 hp tractors. The horsepower is lower than the egine hp beacause the tractor has so many bearings,gears and shafts to get the power from the engine to the pto shaft on the rear of the tractor. A truck or car has much more hp tested at the flywheel vs the wheels.

I was thinking loss would be minimal due to the reduction in speed and torque gain, the gearbox was on my mind because I have one on my bench here that I'm incorporating into a brake lathe build I'm working on.

 

[chadihman]

Ft/lb or ft*lb you know what I mean. Most ways I've seen torque is ft/lb. I guess I just use that because that's what I see on my torque wrench. I didn't even give it a thought. Torque is feet multiplied by pounds or vise versa. Just stay with ft/lb or lb/ft or ft*lb or lb*ft not nm.

 

[drkptt]

...You can also play with the arm-length too, does not have to be a foot long. 5 ft long increases your resolution 5 times, just calculate it in. ...

1 ft/lb on a 1 ft bar would read 1 lb....... 1ft/lb on a 5 ft bar would read 0.2 lb. Your thinking backwards

That is why I said multiply it by 5. (0.2 x 5 =1) Who is thinking backwards again? BTW it is Ft*lb not Ft/lb. It is the product of the two units not the quotient. Good day sir.

I think chadihman had it right the first time. The longer torque arm reduces your resolution. The difference between 1 ft-lb and 1.5 ft-lb as measured by the scale is 0.5 lb for the short arm and 0.1 for the long arm. Longer arm requires a more precise force measurement.

 

[chadihman]

I was thinking loss would be minimal due to the reduction in speed and torque gain, the gearbox was on my mind because I have one on my bench here that I'm incorporating into a brake lathe build I'm working on.

Good thinking Walt. Keep working on yours and I'll work on mine. We can compare how they work differently from each other. Mines not gonna be perfect and I bet yours won't be either. We could learn from each others results.

 

[srcarr52]

I like your thinking too bro. Don't hate me for being an engineer. Cheers,

Oh come on... a real engineer would say go fully automated. Data acq, auto loading, ect.

Load cells are cheap and will be much more accurate than any analog gauge you make. Plus they are easy to read and it takes some of the human factor out. Here are some options.

They say .1oz resolution but I wouldn't trust that since it's a 1mV/V load cell, most are 3mV/V.

Load Cell 25lb Kit with PCB LCD and Software New | eBay

Or a little more expensive but more capable, probably accurate to 0.02 lb with 50lb load cell. Display and load cell sold separately.

Digital Indicator Read Out Load Cell Truck Floor Weigh Scale Animal Peak Vet | eBay

S Type Load Cell Hanging Crane Scale Alloy Steel New | eBay

 

[dynodave]

Wow, you guys are covering a lot of ground in a short time.
Great fun trying to design and build a dyno by committee.:hmm3grin2orange:

Anyway to inject a thinking point of a technical nature.
Hydraulic dyno: Hoses connecting to a pump...if the hose comes off the pump parrallel to the shaft the really stiff 3000psi hydraulic line will resist the twist of the load cell arm and will not completely tell the true torque. Case 2 if you wrap the line like a coil spring than as you increase the hydraulic pressure the hose will try to straighten the line and either add or subtract from the torque measurement depending on the direction of wrap...with or against the shaft rotation.
Kind of like a fire pump hose being held by a fireman who get pushed around like a rag doll from just water pressure.

In summation, I think these considerations may be why my dyno runs a 4-20 milliamp pressure transducer scaled for 0-3000psi. There is no load cell and torque arm like on a water brake dyno.

My future developments for an engine dyno (150hp) will use Labview software ($2500new or like I got an $800 upgrade to the software from work) to run a NI 16 channel A/D (analog/digital) converter card($1000). This is National Instruments stuff...top shelf industrial equipment. I bought it all years ago... Much cheaper is available. But may become technically obsolete quickly. All this stuff goes in a desktop computer and needs custom interface circuits. Goes without saying with 6 years college and 40+ years in electronics/physics and 7 of that in measurement instrumentation, that I can get mine running with 3 different dynos by moving a single 72 pin pluguttahere2:

 

[LegDeLimber]

I think that in the range of power and its variations, it's gonna be tough
to get much more practical than the needle valve, flow meter, combined with
pressure and temp gauges setup.

It won't be lab standard accurate etc,
But I think it would be just fine for comparing saw to saw pulling grunt.

with a few consistent builders and builds,
you probably could pick a group of standard parts
and be able to have a repeatable assembly so that two users could
compare notes from different locations.

But the parts and Assembly configuration and methods
will be the key to comparability

 

[srcarr52]

Wow, you guys are covering a lot of ground in a short time.
Great fun trying to design and build a dyno by committee.:hmm3grin2orange:

Anyway to inject a thinking point of a technical nature.
Hydraulic dyno: Hoses connecting to a pump...if the hose comes off the pump parrallel to the shaft the really stiff 3000psi hydraulic line will resist the twist of the load cell arm and will not completely tell the true torque. Case 2 if you wrap the line like a coil spring than as you increase the hydraulic pressure the hose will try to straighten the line and either add or subtract from the torque measurement depending on the direction of wrap...with or against the shaft rotation.
Kind of like a fire pump hose being held by a fireman who get pushed around like a rag doll from just water pressure.

In summation, I think these considerations may be why my dyno runs a 4-20 milliamp pressure transducer scaled for 0-3000psi. There is no load cell and torque arm like on a water brake dyno.

My future developments for an engine dyno (150hp) will use Labview software ($2500new or like I got an $800 upgrade to the software from work) to run a NI 16 channel A/D (analog/digital) converter card($1000). This is National Instruments stuff...top shelf industrial equipment. I bought it all years ago... Much cheaper is available. But may become technically obsolete quickly. All this stuff goes in a desktop computer and needs custom interface circuits. Goes without saying with 6 years college and 40+ years in electronics/physics and 7 of that in measurement instrumentation, that I can get mine running with 3 different dynos by moving a single 72 pin pluguttahere2:

Proper 90deg fittings and hose routing can minimize the error from them.

As far as hardware/software I worked with NI and Labview and a few others like it in school but I don't have $4k to spend on a chainsaw dyno so I was thinking a solution more like this:

USB Data Acquisition DAQ Kit 8CH 24bit 2DIO w Software | eBay

$100 s-beam style load cell, then put together an instrumentation differential amplifier, that has a input load removing amps, variable gain, shunt and offset for $15 of parts from radio shack, or just buy premade Chinese unit like this for the load cell amplifier that has a stable output voltage to drive the load cell anyway.

http://www.ebay.com/itm/0-5V-10V-4-20mA-Load-Cell-sensor-Amplifier-full-bridge-strain-gauge-transduce-/230937781233?pt=LH_DefaultDomain_0&hash=item35c4f6e3f1

Then a GUI on .NET if you have a free version or some thing free that you can get your hands on. The new graphing in VS2010 is not terrible and would get you by. Or you could use gnuplot or something like that for free.

Only thing I haven't fully figured out is how to use a digital input or a counter to sense RPM. Is the induced voltage from a wire wrap around the high tension lead stable and large enough to be picked up without amplification?

 

[srcarr52]

I think that in the range of power and its variations, it's gonna be tough
to get much more practical than the needle valve, flow meter, combined with
pressure and temp gauges setup.

It won't be lab standard accurate etc,
But I think it would be just fine for comparing saw to saw pulling grunt.

with a few consistent builders and builds,
you probably could pick a group of standard parts
and be able to have a repeatable assembly so that two users could
compare notes from different locations.

But the parts and Assembly configuration and methods
will be the key to comparability

If you want to compare from different locations then you'll have to correct the HP for altitude, temperature and humidity.

 

[Nitroman]

I agree a flywheel setup would be the simplest but what fun is spooling it up and stopping.
I will build this don't worry. I already started ordering some parts. Flea bay is my friend. Please be patient with me as I'm still recovering from sugery. I will start a new thread when I'm finished.

Depends on what you are interested in. If you want to know what the saw is doing, the flywheel is what you want to use. It tells you simply, quickly, and effectively without issues that affect your data (the oil heating/viscosity). PM me if you want some formulas to determine flywheel size and mass.

But if you want to build one where you can load the saw indefinitely then go for it.

This is a direct driven dyno for a 35cc engine producing 18hp.

Using a larger diameter flywheel you can reduce the rotational speed significantly. This is why you see the kart dyno's on eBay having flywheels two feet across. You can easily have a machine shop make a flywheel for you. The software will calculate the drag associated with the drive sprockets, chains and bearings using the spin-down time.

 

[LegDeLimber]

call me a cynic.....
but seems that all the "small details" always keep adding up to why
there appears to be a shortage of these small dynos.

=
Has anyone pondered out the practical issues & mathematics of
pulling a small alternator or generator and dumping it into a load bank?

...any better way to dodge physics rules in that idea??