Yet Another Chainsaw Dyno

[dieseldave]

Been working on a saw dyno, I was impressed by Chad's and decided to do something along the same lines but using a brake instead of hydraulics. The hub, brake, axle, etc. are parts I had lying around from a Honda CR250. I had it up and running tonight and it all seems to work fine, so tomorrow if I get time I will add the torque arm, scale and tach and see how it all works.

 

[Marshy]

Nice work. How much heat do you think that brake is going to generate? If it gets too hot you might cook the brake fluid.

 

[Time's Standing Stihl]

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[burnses]

that's a clever set up the problem you might have is as the pads build heat you will need to change your load on the brake leaver to keep the same load on the engine but nice job and looks like a nice set up to break in a fresh engine and set up the carb without cutting useless cookies of wood...

 

[blsnelling]

that's a clever set up the problem you might have is as the pads build heat you will need to change your load on the brake leaver to keep the same load on the engine but nice job and looks like a nice set up to break in a fresh engine and set up the carb without cutting useless cookies of wood...

I agree. It would be a great tool for tuning inside a shop, but I cannot see it useful for applying a consistent load.

 

[LegDeLimber]

Wonder if we'll get to see it cook a disc?

 

[Blokhead]

Wonder if we'll get to see it cook a disc?

Yeah, that was safe. Hope their insurance adjuster doesn't see the video.


Oh, and nice job on the dyno! Maybe get some race pads to better withstand the heat.

 

[wde_1978]

Wonder if we'll get to see it cook a disc?

Now we know what they do to our cars when they say "leave it here and come back later, we'll have it fixed"!

 

[weimedog]

I plan to do about the same thing.... I have an old rm250 read hub/brake/axle, etc. You beat me to it! Nice concept.

 

[rmh3481]

How about a small generator off an older tractor or an alternator to measure Kw? Maybe even a pump if you can calibrate it.

 

[dieseldave]

A quick post before I go eat dinner- it works. You need 2 guys to run it (at least one of whom is prepared to be soaked in bar oil) as of right now, but I did get some hp #'s and the concept definitely seems viable. So far brake heating is a non-issue- I ran it pretty hard numerous times and never had anything get above 200 degrees. I will be back after I eat

 

[fordf150]

At first glance I thought the same about brakes heating up but after that running it you obviously didn't. One problem you run into that will give inconsistent results is the pads/rotor might glaze over

 

[OldJack]

DieselDave has made a de Prony brake, invented in 1821.
http://en.wikipedia.org/wiki/De_Prony_brake

Brake wear or slippage won't be a problem until it's wore out. Just increase the hydraulic pressure on the brake. What you need to know is the lever arm length between the brake hub and the scale, pressure on the scale and RPM, then do the math.

 

[dieseldave]

A prony brake it is. My lever arm is 12", so my scale reads directly in ft/lbs. Measuring rpm is proving to be a little bit more difficult- for now I am using a hand held digital tach, but it needs a permanently mounted system. I'd like to read the rpm directly off the hub assembly but the saw rpm would work as well. Anyone have any ideas?
The numbers from the brand new, not yet broken in chicom 365 were around 3.7hp at 8500rpm. I'm not at all sure that this was the peak, but it's too difficult to get accurate readings with the hand held tach to do 100rpm increments so that will have to wait. But 3.7 uncorrected, not allowing anything for the parasitic losses, etc, seems to be in the ballpark. I believe that the older 48mm 365's were rated at 4.6, and I'm sure that's measured at the crankshaft on a good day with a tailwind.
rmh3481, I did consider a generator, so much so that I dug one out of storage along with an electric water heater to use as a load bank. I would have to find someone with more electrical knowledge than me to help wire it up so that the field voltage could be adjusted to modulate the load. The plan was to measure the amps and convert into kw. No reason it wouldn't work.
weimedog, If you'd like any detail shots, dimensions, etc, let me know. The nice thing about this contraption is that my entire out of pocket expense was about a hundred bucks for the 24 tooth driven sprocket. Everything else was junk I had lying around.

 

[weedkilla]

I'm curious as to why you chose to gear up the brake end?
You obviously have a reason - it just escapes me.

 

[Marshy]

I'm curious as to why you chose to gear up the brake end?
You obviously have a reason - it just escapes me.

My guess is less speed = less heat and wear on the brake.

 

[dieseldave]

It's geared down- the sprocket on the saw is a 7 pin, the one the hub is 24, giving a reduction of 3.43 or so. I would have geared it down further but the 24 pin sprocket was the biggest I could find.

 

[weedkilla]

Oh geez. Numpty moment.

I might have to hit you up for the source of the 24t

 

[CR888]

We all need a saw dino!! Congrats to the op and keep us in the loop with any testing and stuff. Nothing better than reading saw dino data on the can. What a good tuning device as well. Exhaust extraction is a good idea if using indoors.

 

[dieseldave]

Here's a quick vid of the dyno in action