Verify my calculation, bending moment torque

In summary, the conversation is about a homemade engine dynamometer that the person is trying to design. They ask for assistance in understanding the diagram and the concept behind it. There are some questions and clarifications about the design, and the person also mentions other types of dynamometers and their own ideas for a "poor man's dyno." They share another diagram to explain their design better, and ask for feedback and suggestions from the other person.
  • #1
WhiteHawk
10
0
I made a diagram with the calcs on it, should be fairly simple, I just need to make sure I'm doing it right or if I'm way off.

link to the diagram

These are the beginnings of my homemade engine dynamometer...I thank you for your assistance.
 
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  • #2
where did this moved?
 
  • #3
I'm sorry but I don't understand the diagram. Is one corner pinned? What does the 300 ft-lb represent? What does the force represent?

I believe, however, you have a mistake. You have ft-lb * ft = lb and that is not true.

I'm not sure what sort of dynamometer you're making, but are you aware of prony brakes?
 
  • #4
TVP45 said:
I'm sorry but I don't understand the diagram. Is one corner pinned? What does the 300 ft-lb represent? What does the force represent?

I believe, however, you have a mistake. You have ft-lb * ft = lb and that is not true.

I'm not sure what sort of dynamometer you're making, but are you aware of prony brakes?

The square is real (mechanical object with no deflection). The one corner labled "bending moment" is on a pivot bearing, the square would rotate around that point. There is 300 ftlbs of torque being applied to the other point. The system would not actually move (with this design I would use a transducer to measure the force). Basically I would need a way to calculate the torque by measuring how much force (lbs or N) applied where I have the "?", so I can calculate HP with RPM.

As far as prony brakes, I think with the high output of a V8 engine wouldn't be practical for that design. Basically any way of efficiently braking the engine under wide open throttle to hold at specific RPMs would be a dynamometer. The most popular designs are a water pump that you restrict the outlet causing resistance or using a very large generator to create resistance. For my poor mans dyno idea, I would use a rear axle out of a truck, with large disc brakes to create the resistance.

So this theoretical torque I mention above is coming from the input shaft of the rear axle, and the axle would be mounted at that pivot point 6" from the center of the input shaft.
 
  • #5
If I understand your diagram correctly (and I may not, so correct me), you have a rigid structure (the square) with a pivot at the lower left corner. There is a 300 ft-lb torque applied ABOUT the upper left corner (This is where I may not understand you. I read the curved arrow to indicate that the centerline of the input shaft is perpendicular to the square and points right at that upper left corner. Is that OK). You want to resist (and measure) the torque at the lower right corner.

If that is correct, the structure is probably not free to rotate about the pivot. The pivot will actually oppose the turning torque and there will be little if anything to measure. The exception to this is if the motor and shaft are actually mounted on the square and free to turn with it; in that case, it may destroy itself or not but that seems a difficult way (and dangerous one) to do the measurement.

Can you give more details? Thanks.
Tom
 
  • #6
I drew another diagram, with how I could maybe represent the scenario a little better.

Blue circle is the pivot.

Green circle is input torque.

Tan box is force measuring device.

The Important item, is the Magical Red lever to signify the torque, is this lever valid? See how I drew it standing vertical, it would seem as though the system would want to pivot now.

New Diagram
 
  • #7
I still can't see clearly, but it looks like it doesn't quite work. Is the green circle connected to something which is connected to the earth? Or very heavy?
 
  • #8
TVP45 said:
I still can't see clearly, but it looks like it doesn't quite work. Is the green circle connected to something which is connected to the earth? Or very heavy?

The green circle is floating and can "move" with the system. A driveshaft with universal joints would be driving the green circle (like a car suspension can flex while the driveshaft is still able to turn).
 

1. What is bending moment torque?

Bending moment torque is a measure of the force applied to an object that causes it to rotate around an axis.

2. How do I calculate bending moment torque?

To calculate bending moment torque, you need to know the force applied to the object, the distance from the axis of rotation, and the angle between the force and the lever arm. The formula for bending moment torque is T = F x d x sinθ, where T is the torque, F is the force, d is the distance, and θ is the angle.

3. Why is it important to verify my calculation of bending moment torque?

Verifying your calculation of bending moment torque is important to ensure the accuracy of your results. Even small errors in calculation can have a significant impact on the outcome and may lead to incorrect conclusions.

4. What are some common mistakes to avoid when calculating bending moment torque?

Some common mistakes to avoid when calculating bending moment torque include using the wrong formula, using incorrect units, and not taking into account the direction of the force and the lever arm. It is also important to double check your calculations and use precise measurements.

5. Can bending moment torque be negative?

Yes, bending moment torque can be negative if the force and the lever arm are in opposite directions. This indicates that the object will rotate in the opposite direction than if the torque were positive.

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