Chainsaw dynometer build.

[Mastermind]

From a 6 tooth drive to a 16 tooth driven is a ratio of 2.67:1 so if the pre loaded engine rpm is 12000 the pump is 4500 rpm. Max rpm of my pump is 4000 rpm. I'll be pushing that a bit. Most saws get there max torque at 9600 rpms or lower. 9600 on the saw would be 3600 rpm on the pump. I'll just start the saw on a slight pre loaded setting. The 16 tooth sprocket I have is 3.5" so its perfect for matching the cut off bar I'm using.

A jackshaft may be used to further change the ratio.....

 

[Simonizer]

This is a little sketch I drew up to explain a little better.

Why not scrap the load cell and use a spring scale? You could easily zero it to account for the weight of the arm at start-up. You could also scrap the whole arm/scale idea and drive the pump with a thin torsion bar and measure the angular deflection between the two ends. Torque is torque no matter what means you use to measure it.

 

[Mastermind]

Here's a good write up on a fluid brake dyno.....

Karting Dynomometers Part 2 - Fluid Brake Dynos - Article by John Copeland

If I broke a rule by posting this please let me know......

 

[Homelite410]

Correct me if I am wrong here, but doesn't oregon offer a "W" series cutterless chain. Btw I really like this idea and good luck to anyone who is helping along the way!

 

[watsonr]

Here's a good write up on a fluid brake dyno.....

Karting Dynomometers Part 2 - Fluid Brake Dynos - Article by John Copeland

If I broke a rule by posting this please let me know......

We have come to except this from you... we ALL know your a rule breaker!:hmm3grin2orange:

 

[Mastermind]

We have come to except this from you... we ALL know your a rule breaker!:hmm3grin2orange:

I got a yellow mark from Bob the other day. :msp_unsure:

 

[chadihman]

Why not scrap the load cell and use a spring scale? You could easily zero it to account for the weight of the arm at start-up. You could also scrap the whole arm/scale idea and drive the pump with a thin torsion bar and measure the angular deflection between the two ends. Torque is torque no matter what means you use to measure it.

Yes a spring scale would work but it would be hard to get small change readings in a saw that has 3 ft lbs torque. A one foot arm on the pump with 3 ft/lb torque will read 3 lb on the measuring devise. Lets say I advace the timing on the saw and want to see the + or - gain. How would I accurately measure a .005 gain in lbs without a electronic measuring device? A spring scale might be alright for larger engines with lots more torque but not for an engine that has really low torque.
Don't get me wrong. I really like everyones I deas.

 

[chadihman]

A jackshaft may be used to further change the ratio.....

Yup I'll use a jackshaft to lower the rpms if I have to but I'm not wild about that idea. The more barings,gears,belts and sprockets the more drag before the pump. I want to stick with as little moving parts as posible before the pump. Who cares if the pump has drag as that will be shown on the scale but any drag before the pump will not be shown.

 

[Simonizer]

Yes a spring scale would work but it would be hard to get small change readings in a saw that has 3 ft lbs torque. A one foot arm on the pump with 3 ft/lb torque will read 3 lb on the measuring devise. Lets say I advace the timing on the saw and want to see the + or - gain. How would I accurately measure a .005 gain in lbs without a electronic measuring device? A spring scale might be alright for larger engines with lots more torque but not for an engine that has really low torque.
Don't get me wrong. I really like everyones I deas.

Have a few different scales with different ranges, they are cheap. 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. What IS important is keeping the scale perpendicular to the arm. I would measure in ft-oz and then just divide by 16 to get to lbs and multiply by (x) to account for arm length in (x) ft.

 

[Mastermind]

Yes a spring scale would work but it would be hard to get small change readings in a saw that has 3 ft lbs torque. A one foot arm on the pump with 3 ft/lb torque will read 3 lb on the measuring devise. Lets say I advace the timing on the saw and want to see the + or - gain. How would I accurately measure a .005 gain in lbs without a electronic measuring device? A spring scale might be alright for larger engines with lots more torque but not for an engine that has really low torque.
Don't get me wrong. I really like everyones I deas.

If I'm reading everything I see on hydraulic pumps correctly you can use pressure readings to determine torque.....

 

[Mastermind]

Yup I'll use a jackshaft to lower the rpms if I have to but I'm not wild about that idea. The more barings,gears,belts and sprockets the more drag before the pump. I want to stick with as little moving parts as posible before the pump. Who cares if the pump has drag as that will be shown on the scale but any drag before the pump will not be shown.

Yeah I thought about the increase of torque through gearing, but figured that could be accounted for. One other thing to consider is oil temp......it would need to be constant to obtain consistent readings; would it not?

 

[Simonizer]

If I'm reading everything I see on hydraulic pumps correctly you can use pressure readings to determine torque.....

That introduces too much error though Randy. For 100hp and above it becomes insignificant but for 10hp and less the variables in friction, viscosity losses, heat in general, really muddies the waters.

 

[Mastermind]

That introduces too much error though Randy. For 100hp and above it becomes insignificant but for 10hp and less the variables in friction, viscosity losses, heat in general, really muddies the waters.

I see. I've been doing some reading on the subject Simon.......but have exactly zero experience on this. Thanks for your input. :msp_thumbup:

 

[RiverRat2]

Yeah I thought about the increase of torque through gearing, but figured that could be accounted for. One other thing to consider is oil temp......it would need to be constant to obtain consistent readings; would it not?

That introduces too much error though Randy. For 100hp and above it becomes insignificant but for 10hp and less the variables in friction, viscosity losses, heat in general, really muddies the waters.

I just love it when you guys use those big words like trailer-house and watermelon,,,,

 

[Mastermind]

I just love it when you guys use those big words like trailer-house and watermelon,,,,

Yeah, my eighth grade education is showing......

 

[chadihman]

Have a few different scales with different ranges, they are cheap. 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. What IS important is keeping the scale perpendicular to the arm. I would measure in ft-oz and then just divide by 16 to get to lbs and multiply by (x) to account for arm length in (x) ft.

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

 

[chadihman]

Yeah I thought about the increase of torque through gearing, but figured that could be accounted for. One other thing to consider is oil temp......it would need to be constant to obtain consistent readings; would it not?

Oil temp would change the braking a little. All you have to do is adjust the needle valve to dial it in again.

 

[srcarr52]

If I'm reading everything I see on hydraulic pumps correctly you can use pressure readings to determine torque.....

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

 

[chadihman]

Think about it this way. The needle valve is set to hold the saw at 9600 rpms as the hyd oil heats up the oil gets thinner and the less oil is being pumped and there will be less pressure on the scale and the saw should gain a little rpm. Just adjust the needle valve a little further shut to pull the saw down to 9600 rpms again. Oil temp shouldn't be a problem here. The pump is small with low flow and the torque it's holding back is low. My 3 gal tank will also help keep it cool.

Dammm all this talking about this is drivin me freekin nuts. Come on ups get my parts here already:bang: I wanna build it now. I havent been this excited in awhile.uttahere2: No I'm not jumping up and down like that. My rear is still healing. Just got my stitches out this morning.

 

[Walt41]

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.