Can Torque Be Translated?

<Torque is usually taken off by a 'load'>

We always learnt that Torque is CAUSED BY THE LOAD or rather-No load -no torque needs to develope.

By 'Load' I mean a brake of sorts, either electrical, mechanical, friction or by air paddles or whatever.

The "load" will load down the engine or motor.

Hello Guest,

Long ago we learned the same.

Without a load, torque cannot exist.

Kind Regards....

Ken, thank you for a great answer.

I agree with you that the weight of the base plate would have to be considered as well.

To overcome that, perhaps the base plate is suspended by some frame members from above, where the hinge point is above the centre of gravity of the total assembly, and a load cell is placed horizontally below the base plate bearing against a short vertical arm extension from under the base plate. I don't know how to add a graph like you did, so the description hopefully is adequate.

I would think that the force on the load cell times the distance from load cell to hinge point above, would equal the torque put out by the driving machinery mounted on the base plate. Would you agree with that?

It should work if the power is transmitted via a shaft with a universal joint, or even sideways with a belt and pulley.

Regards

Rolf

Are you thinking of this purely theoretically or pragmatically?

In a pragmatic sense, you can simply cancel the weight by resetting or recalibrating the load cell. Of course, you need to be aware that anything that changes the weight then means the machine needs to be re-zeroed.

Putting a universal joint in the connection between motor and brake makes quite a difference. If the connection is rigid, the the rotation of the frame has to be around the motor shaft/brake shaft, in which case the whole frame is acting as a traditional torque arm. In this case a second hinge pivot would prevent rotation and prevent sensing of torque (assuming the frame does not deflect substantially).

You can experiment with a board with several bolts in various locations. If you tighten these with a socket wrench with an extension and a universal joint, then the torque experience by the board around a pivoting corner would be the same for each of the bolts. You'd have to use both hands to transmit torque through the universal shaft. If instead, you used a socket wrench handle without an extension, then the situation is much different. Depending upon the bolt location and handle location, the torque experienced by the board (around its corner) will vary. The handle length can add to the total arm, or subtract from it. (You may have noticed this in tightening wheel bolts-- if the handle crosses over the axle, then the wheel torque, for a given bolt torque, is lower than it would be if the handle extends out beyond the circumference of the tire. )

The only condition in which belt tension would not pull either away from or toward the load cell would be if the two pulleys and the frame hinge are all in line. For a given torque, belt tension would depend upon pulley size.

Pragmatics would suggest that you'd want to use a traditional torque arm if possible. Then any vibrations in the system would be easier to eliminate or filter out and the magnitude of forces from resonances would be lower. But as others have said, there are all sorts of torque sensors that simply measure things like motor mount deflection.

If this is a practical application, then the other type of dyno, in which you measure torque indirectly by the rate at which you can accelerate a flywheel, should be considered.

Thanks Ken.

The tire tightening (or loosening) is a good example.

It is intended as a practical case. From all said so far, perhaps it really would be best and the safest to mount the support frame rotably in line with the drive shaft and have a torque arm measured from the centre of rotation (drive shaft). This way, no compensation of any kind is necessary.

Alternatively, we are thinking also of using an AC or DC generator and measure Volt and Amps, calculating hp this way directly.

Some electrical expert would have to advise what the efficiency is at various load and rpm settings. Something to do with the power factor, I trust?

Regards

Rolf.

I have a couple DC motors which I will be using on my prototype (in the little picture) Each came with a dyno trace actually measured on the individual motor (100% testing). These reports show efficiency at the full range of operating rpms (although the ones with my motors only show full load efficiencies. I suppose you could run a DC generator output through a grid-tie inverter, and sell the power generated to the utility company. Otherwise, you end up having to heat up something with any dyno, and unless you have a need for hot oil, hot water, or hot air, all that energy is wasted. With AC, this would be a little trickier, because you need to first rectify the AC to be able to invert it to a stable frequency.

About 30 years ago, I built a couple hydraulic chassis dynos for motorcycles. In them, torque was measured as a function of hydraulic pressure, with the wheel roller driving a gear (or it may have been a geroler) pump. The resistance for the hydraulic pump was a simple valve, not much different that a garden hose bib. I used a $2.00 optical pickup (chopper) for speed sensing. The frame was the hydraulic tank -- I'd guess it was about 100 gallons -- and it never became uncomfortably warm. Probably a little simpler than an electric solution, although the two are very close. Smoothly varying control of a lot of amperage can be expensive, so the cost difference might depend on the amount of HP to be measured. But in any case, hydraulics are worth considering -- very easy, straightforward, and compact (except for the tank).

¡Gracias por la buena respuesta! Considere por favor el colocarse como miembro - hay lejano demasiadas "huéspedes" a no perder de vista.

Thank you for your answer, Luis.

I trust what you said is essentially that torque can also be measured by a frame on which it is acting upon. Thanks.

Rolf

It really wouldn't matter what length the torque arm is. To yield useful information the system will require calibration over the entire range of torque values.

The calibration information and your instrumentation's linearization and zero offset capabilities should compensate for static loading at zero torque and match the calibration standard at maximum torque.

Point well taken.

With the proper calibration the weight of the baseplate and motor should not matter. Thanks.

Rolf

Thjis is essentially th operation of many torque motors. Large aircraft recips used the drag on the spider ring of a planetary gear reducer to the prop. Many smaller ones measure the load on the motor mounts. Load cells probably replaced the hydraulic pots used in the old days. I would imagine that larger ship engines with a direct-coupled shaft would use a frame mounted sensor. For multi-engine craft load combined with fuel consumption is critical for maintaining efficiency. Regulated rpm, such as multi-engine aircraft use to prevent destructive vibration can leave one engine with a lower-pitched prop to maintain the same rpm, resulting in excess trimming and drag. There are many situations where torque is monitored to adjust feed rates and other loads for improved efficiency.

RichH

"At its outer end the force of the arm is measured in N or lb (force)."

Surely you mean weight. Force is the product of mass and acceleration!

As far as torque is concerned it is the product of a distance, a vector quantity, and a weight of N or lb and is maintained anywhere in a plane perpendicular to the axis of rotation.

Surely you mean weight. Force is the product of mass and acceleration!

He's correct in saying force. Weight is a product of mass and acceleration, with the acceleration being that due to gravity. (We "weigh" less on the moon.) For measuring torque, especially, the distinction is important, because the force at the end of the arm may or may not be aligned with gravity. (Many dynamometers would read correctly on the moon.)

A very large torque wrench can apply significant torque to a tiny fastener with the handle horizontal and unsupported. The torque applied is equal to the weight of the wrench acting at its center of gravity. Any additional force applied to the handle by hand can either add to the force of weight or subtract from it.

[In the US, we correctly use pounds as a unit of weight. In Europe, if you ask someone how much they "weigh" you get the answer in units of mass (i.e kg rather than newtons)*. In the US however, we rarely use units of mass (although in fluid flow, we often use "slugs") or make the distinction between pound force and pound mass. This link talks about the three systems used (SI, BG and EE).)

BTW distance is not, by itself, a vector quantity. A distance and direction together is a vector quantity.

*Therefore, Europeans weigh the same on the moon as on earth: 70 kg is 70 kg. Americans weigh less on the moon: 150 lb here is 25 lb on the moon.