Dynamometers

A client just asked me if I knew of any testing house that had a dynamometer suitable for testing their stuff.

We're looking at something that can accurately measure torques from 0 to about 100 N-m, at speeds from 0 to 80 RPM or so. Something suitable for a full-race 502 is probably out of place here.

If you know of such a place, or if you have suggestions for where to get or make an affordable dynamometer that's accurate to +/- 5 N-m or so, let me know.

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Tim Wescott 
Wescott Design Services 
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Tim Wescott
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Tim Wescott fired this volley in news:k7adnTdGp6TObS snipped-for-privacy@giganews.com:

Why? Will they only measure at high speeds? Torque is torque, yes?

Lloyd

Reply to
Lloyd E. Sponenburgh

Den tirsdag den 1. juli 2014 19.30.59 UTC+2 skrev Tim Wescott:

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does it have to be a static load? a lot of dynos for cars are really just a big flywheel with a know moment of inertia speed is logged and the power/torque curves is calculated from the acceleration

-Lasse

Reply to
Lasse Langwadt Christensen

We used to attach generators and vary the load, that way you could get a lot of almost direct measurements at all kinds of speed torque-curves.

Reply to
RobertMacy

Torque is torque, yes, but if you need to weigh an envelope to see how many stamps to put on it you don't head out to the nearest truck scale.

And yes, to my knowledge many of the cost-effective ways to make engine and chassis dynamometers are speed-sensitive.

I suspect that the instrument they want to calibrate wouldn't even be able to overcome the friction on an engine dynamometer, much less be in a range where the measurement will be accurate.

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Tim Wescott 
Wescott Design Services 
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Tim Wescott

Den tirsdag den 1. juli 2014 20.10.05 UTC+2 skrev Robert Macy:

yeh, something like an alternator and a load but at 80 rpm the speed is too low you'd need gearing

-Lasse

Reply to
Lasse Langwadt Christensen

Tim Wescott fired this volley in news:k7adnTZGp6QxYS snipped-for-privacy@giganews.com:

And likely calibrated over the entire range of rpms...

Even a top fuel dragster _starts_ at zero rpm, and the torque at the low end (as transferred to the axle) is as important as high-end torque.

Lloyd

Reply to
Lloyd E. Sponenburgh

We're verifying the control system as much as the motor and mechanism, and the control system has dynamics that would preclude that.

Besides, you'd either need a flywheel as big as a house, on nearly frictionless bearings, or you'd need gearing that would mess up your nice torque calibrations.

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Tim Wescott 
Wescott Design Services 
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Tim Wescott

on a car dynos you just push the clutch and keep measuring while coasting to a stop and use that to subtract the friction and losses

disc brake with the caliper on a load cell?

-Lasse

Reply to
Lasse Langwadt Christensen

AC induction and shaded-pole motors make nice adjustable brakes if you run some DC into the windings. You could measure the torque on the motor case pretty easily, an arm connected to a scale of some sort.

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John Larkin         Highland Technology, Inc 

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John Larkin

Den tirsdag den 1. juli 2014 22.23.04 UTC+2 skrev John Larkin:

but not at 80rpm

-Lasse

Reply to
Lasse Langwadt Christensen

Or worse, 1 RPM.

Reply to
Tom Miller

For smaller cases like this, a DC permanent-magnet brush motor can make a VERY good dyno. A resistor bank and an ammeter are the other things you need. A shunt-wound motor is even better, as you can vary the load with a small rheostat or an adjustable DC supply.

Jon

Reply to
Jon Elson

Why not? That's what they normally run at.

(Wait for it... :-) )

Tim

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Seven Transistor Labs 
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Tim Williams

Den tirsdag den 1. juli 2014 23.14.16 UTC+2 skrev Tim Williams:

the torque and speed would fit something like an exercise bike ;)

-Lasse

Reply to
Lasse Langwadt Christensen

My problem isn't figuring out how to _make_ a dynamometer if it comes to that -- I've got 10^bazzilion ideas about that.

My problem is that my customer would prefer to buy the service from a lab, or buy a dynamometer with calibrations & all that stuff.

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Tim Wescott 
Wescott Design Services 
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Tim Wescott

Oh that's no fun! You'll have to tell your customer that SED is not interested, and that it will cost more. :^) (I was thinking of a copper disc spinning in magnetic field, but it's hard to get to 100N-m..)

George H.

Reply to
George Herold

I used to design reel-reel tape decks. The reel motors were AC induction motors, and the payout reels turned pretty slow. A little DC gave a nice braking force.

Step it up with a toothed belt, if that helps.

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John Larkin         Highland Technology, Inc 

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John Larkin

Build one, they are not complicated.

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Steve W.
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Steve W.

But the torque at anything under about 3000 RPM is not measured because the engine can't run that slow..

What the OP needs is a "prony brake" which is relatively easy to build and calibrate, or an "eddy current dyno cell" made out of an electric motor or generator and a load resistor. Both require either apressure transducer or a scale of some sort to measure the force on the reaction arm.

Reply to
clare

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