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What are Dynamometers?

By Shannon Kietzman
Updated May 17, 2024
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Dynamometers are specialized instruments used to measure an engine's revolutions per minute (RPM) and torque. RPM is a measurement of the number of times the crankshaft revolves inside an engine. The more revolutions a crankshaft makes each minute, the faster and more powerful the engine is.

There are many parts inside a car's engine, including the crankshaft and pistons. The crankshaft is similar to a bicycle's pedals, with the bicyclist's legs being the pistons. The pistons push the crankshaft and cause it to rotate. As a result, the crankshaft causes the drive shaft, which is like the bicycle's chain, to move. This causes the axle and tires to rotate, making the car move.

RPM must be within a specific range in order for a person's automobile to run smoothly and efficiently. Incorrect engine measurements can be a sign of engine troubles. Dynamometers allow the car owner or mechanic to test the RPM to ensure it is where it needs to be.

Charles Babbage, often referred to as the "Father of Computing," created the first dynamometers in the late 19th century. As a mathematician and engineer, he realized the vast margin of error found in many mathematical tables. Therefore, his dream was to create a machine that could do math without error.

Many credit Charles Babbage for coming up with the idea behind computers. Using the same concept, however, he also realized a machine could be created to count the number of times an engine caused a vehicle's tires to turn. Hence, dynamometers were born.

Charles Babbage's original dynamometers developed into two machines. One, called an engine dynamometer, is attached directly to the engine. Engine dynamometers require the engine to be removed from the vehicle before measurements can take place. Therefore, it is not always the most practical option.

Chassis dynamometers are the other type. These dynamometers allow people to read the RPM without removing the engine. The vehicle's tires are placed on the chassis dynamometer's rollers and the vehicle is revved up to a certain speed. Chassis dynamometers give readings of the car's horsepower output as well as how many times the tires have revolved.

Both types of dynamometers absorb power from a running engine and measure the torque required to absorb that power. Once the machine has those readings, it calculates the engine's RPM. Many dynamometers today are hooked up to computers, which can graph the engine's capabilities and output.

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Discussion Comments
By David09 — On Oct 27, 2011

@MrMoody - I prefer the computerized version of the technology myself. You can buy dynamometer software for your car to get actual readings on how the engine is revving.

That’s better than simply listening for strange sounds to determine if the car is operating normally.

I remember I had a problem with my Honda where it would idle high when I was at a stop light, and rev back and forth, making a whole bunch of noises.

It was embarrassing because it made it sound like I was trying to race the guy next to me! When I drove normally, it would rev fine. I wish I had had a dynamometer software application at the time, so that I could keep continual recordings of how the engine was actually performing.

Then, when I brought it to the mechanic they would have actual data to look at, rather than hoping they could duplicate the same condition in the shop, which they could not always do sad to say.

By MrMoody — On Oct 26, 2011

@Charred - I read once that he had used it take measurements on a railroad engine. I think he installed his device on a car attached to the train and recorded information on rolls of paper.

I don’t know if this would classify it as a chassis dynamometer or an engine dynamometer. The device moved with the train, so it’s not like it was static or anything.

At any rate I always find it fascinating that the underpinnings of so many modern inventions have their roots in early machinery that used things like wooden gears and pulleys to implement the basic concepts of the invention.

By Charred — On Oct 25, 2011

I knew about Charles Babbage and his connection to the personal computer, but was unaware that he was also partly responsible for the dynamometer.

I guess it would make sense when you think about it. In those days, many inventions relied on the rotations of moving parts; these were before the days of transistors and silicon chips and things like that.

Therefore I can understand how the technology used for the dynamometer could be the same technology used for a simple primitive computer. The only thing I would wonder about is in what capacity Charles Babbage used this device?

Was he measuring the engines of a steam engine or perhaps the machinery behind a loom or something like that?

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