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

[wcorey]

I don't remember the final numbers on mine but made a template to use as a reference and drill jig in case I ever want to make another. In practical terms an even pin count/ratio wasn't really important or necessary because you could just plug the ratio into the software and it got calculated in auto-magically.

To figure the diameter I just gave it a close estimate then turned a disk out of thin, like 14ga, steel and brought it down in .005" increments until things lined up for 35 pins.
Then went to 10ga for the jig and ultimately the two outside halves of the sprocket.

Made one for .325 and one for 3/8ths that also works for 3/8lp

Keep in mind for pin placement that your 28 pin sprocket is being driven by the chain rather than the 7 pin that's driving the chain (so opposite wear surfaces), unless maybe your going to use design specific (expensive) drive chain...

 

[wcorey]

You might want to check out the 'saw dyno' thread on the 'other power equipment forum', goes back to 2016 or so.
Sorry I cant post links here...

 

[Walter Glover]

Thank you Bill. Your sprocket is the way i figured to pin mine as well. Got disks nearly trued up to rotary table. Need to mount a suitable plate for the divisions then drill some holes. Have some very hard 0.156” rod here to cut up for pins. Hope that works

 

[wcorey]

I used dowel pins, something like drill rod would likely be fine too, drilled stepped holes so the pins are captive when the halves are bolted together.
IIRC Chad had an issue with the pressed in pins wallowing out of the holes.
The pins weren't so much of a wear issue on mine but rather the edge of the sprocket plates where the chain side plates ride.

 

[Walter Glover]

Had to make a 42 hole circle for the rotary table to allow 28 divisions. Had an aluminum casting that had issues so made a fixture to hold the sprocket disks. Worked great for indicating the disks in. Pilot hole through both plates together as they will be then seperated to drill the insides out to pin diameter. Went about 0.175” into the 1/4” plate. That will capture the pins for sure. Thanks for the tip, I like it and making the jig really made it easy.

 

[Walter Glover]

Progress

 

[Walter Glover]

Purchased some vintage instrumentation to see the results
An 20 pound hanging scale and an analog phototach with multiple ranges.
The beauty of analog measurement is the ease of determining a good average or even peak value. Digital displays just don't work
for erratic values. So hope this works out eh

 

[wcorey]

Averaging is key, whether digital or analog.
Peak doesn't mean much of anything unless it's averaged over a reasonable period of time.
Grab a handful of brake and you can see a torque spike for a fleeting moment ten times what a two second average would be and it's near impossible to nail down the rpm where it happened.

 

[Walter Glover]

No intention of grabbing the brake as you say that proves nothing. Analog dials are perfect for determining quickly what an average value might be.
As an electrician I never liked digital meters for moving values ie balancing a pumpjack based on motor current. Was so much easier with old school analog.

 

[Walter Glover]

Received the scale. Big bold numbers on an eight inch dial. Commercial duty scale and accurate. Should work great for the dyno

 

[Walter Glover]

Got the photo tach but not impressed for sustained readings so will use an engine tach with a mag pickup sensing the four sprocket bolt heads. This makes an eight cylinder tach read correctly. Had to make a little adapter circuit to amplify the small mag signal. Internet is great for finding stuff like that. Made the adapter and tach works great!
Making progress for sure

 

[Walter Glover]

Progress today. Finished the mechanical bits and gave it a run. Many issues reared up that need fixing.

 

[Walter Glover]

Worked on it some more this aft.
went with a hydraulic force sensor
Made bushings to align saw in bar mount
Made a knob to fine adjust brake caliber lever
Will do some runs tomorrow if all goes well

 

[Walter Glover]

Got it back together and did a couple runs with my 372xp kit saw. Could only get 2.85hp out of it. Best it did was 7.5 pounds torque on dyno at 2000 rpm thinking my force measurement needs help. Onwards.....,

 

[Walter Glover]