Here's one I've saved.
I haven't found my copy of John DeArmond's 1989 or so description of his home
made dyno, but I do remember that it was water cooled- you need to get rid of
both the engine heat, and the heat of friction generated by the mechanical,
hydraulic, or whatever brake used, and that's a lot of heat. You also have to
provide for muffler and exhaust connections to the outside.
-------------------
In article <3068@uceng.UC.EDU> shartman@uceng.UC.EDU (sam hartman) writes:
>
> I am trying to work out a project to take a motor or internal
>combustion engine and measure horse power. Has anyone evr done this, say
>in their garage? What I need is some kind of mechanical device that I can
>build and then calculate a fairly accurate reading. Thanks in advance.
>
> shartman@uceng.uc.edu
A friend of mine built a small (well, sort of) dyno about a year and a half
ago. It consists of a frame made of 2.5" square tubing, about 2' high by
3' wide by 7' long. The engine sits on a mount which is bolted to the
top rails. The stock engine's flywheel and starter are used. Power is
transmitted from the flywheel to a disc which serves as an adapter
for all the different clutch bolt patterns. Then we go on through a Datsun
halfshaft (mounted in a safety hoop - gotta be careful here) and to two
12" x 1", 4130 (I think) steel disks. The disks act on a set of automotive
brake calipers, which are mounted in a frame. The frame is set in bearings
on the disk shaft, and is kept from rotating by a hydraulic cylinder.
The hydraulic cylinder just happens to have a piston are of 1 square inch,
and is mounted so the lever arm is one foot. The pressure in the cylinder
is monitored using a large damped pressure gauge (0-500 psi). We have
a brake master cylinder with a threaded pushrod, which applies the brakes.
The engine is cooled using a large radiator, mounted inside a water bath.
The flow of water through the bath controls engine temperature; water is
also used to cool the brake rotors.
Then we use hp = speed (rpm) x torque (ft-lbs) / 5252.
This design has proven to be quite repeatable up to about 200 hp. It is
essential to carefully warm up the brakes to get smooth torque readings.
We may add an additional shock damper on the brake arm.
Disclaimer: When we do dyno runs, NOBODY stands between the plane of the
engine flywheel and the rear of the dyno where the brakes are. We're
confident we've overdesigned it reasonably well, and so far it's proven
safe to 8000 rpm, but we're not taking chances.
Theo Smit (smit@enel.ucalgary.ca)
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