Very good presentation. Thank goodness for a video with clear diction, good explanation of the science and engineering involved- and a lack of stupid music!
What a pleasure to watch someone explain in first principle terms how to measure engine output. Your method would hopefully also demonstrate to youngsters the relationship between torque and horsepower, well done sir, thoroughly enjoyed you videos.
I should have learned this in physics class back in 1966, I guess the instructor didn't think it was relevant. This is the sort of demonstration that really gets a kids attention, especially if he has an interest in mechanical things.
I recently graduated with a mechanical engineering degree. It is an utter shame demonstrations like this aren't a staple of today's education. Extremely interesting video.
I had the privilage to see Amos Rixman and his Prony Brake at a tractor show at Rosebud, Mo. years ago hooked up to a steam traction engine and also to my Cat D2 with p.t.o..That steam engine sounded like music as its slow RPM pulled against the brake. He said it was pulling more torque than a semi going down the highway or a hot rod car. Thanks and stay cool at the summer shows.
Great video. I always wanted to make a prony brake and take it to shows, didn't know it was so simple but I remember reading the math. Nice to have someone use the English terminology, newton-meters just doesn't sound right and sometimes you here the term lbs.-ft. which really bugs me instead of ft.-lbs. because ( I think) some one is converting from metric to English and meters-newtons doesn't sound right in metric system
Dear sir. Thanks for showing this. If you would not have done this, than I would never have known this, not that I would be unable to live, but knowledge is power.
Hope you are still fiddling with engines! We used to have a "Z" F&,M engine on the farm in central Cal. I restored a John Deere 1929 model "GP" orchard tractor still on "steel" ( lol) Got it when I was 12 for $25. Cost $25 to have the magneto rebuilt at the time.ran it for years for fun, ran great. Keep up the great work! Hope to see more good stuff/science. Regards, Doug
You could flip the arm around so it pushes down and use a springless scale on it. At old threshers in mt. Pleasant ia we have a prony brake there but we use a different formula we use weight x rpm divided by 1000 the scale is a fairbanks morse springless scale and also when you use yours you need to take the rpm mesurement right when you have the weight on but that might take 2 people
i wish i had a reason to try this, but my life is full of small electric motors, unlike anything you show us in your great videos. still - i'm learning and it's fun. thanks :-)
Wow. It´s been nice watching both of your videos. I was looking for ideas on how to use the Prony brake(which I've heard of so many years ago at the school) to find out how much power does an small motorcycle have by measuring the power by braking the rear (driving) wheel. Not because I need to, but for fun, I'm willing to perform a couple modifications to the engine to gain a little more power and I need a way of measuring what works and what doesn't. You know, nowadays guys go to tunning shops whom own pretty fancy expensive dinamometers, no doubt they're much more flexible and precise, yet these "old school" methods apply the same old principles. I'm sure if one is careful enough -like yourself- measurings must result pretty much the same like the one would get out of the fancy expensive tools. BTW in case you wonder I'm in Argentina, so I apologize for my funny English (not my mother tongue, apologies) Thanks a lot!
The word "dynamometer" brings to mind using a belt driven generator instead of a prony brake. It would not be that long (in terms of history) before electrical generators would be developed after the steam/gas engines and prony brake. In the *dynamometer* measurement idea, an electrical generator is wired to a bank of resistors (light bulbs) in order to put a variable 'electrical load' on the generator. The loaded generator would, in turn, put a torque (load) onto the engine's shaft. By adjusting the number of lights (resistors) connected to the generator's circuit, the maximum engine torque can be applied without the engine losing speed (from its rated speed). The electrical output from the generator at this max point, would, in Kilowatts be a measurement of the engine's horsepower ( 0.7457 KW = 1 HP). There are small power losses associated with a belt drive; so, for the most accurate measurement, the dynamometer (i.e.: generator-bank of adjustable resistors) needs to be directly connected to the shaft of the engine. But still, with a belt driven, home-made dynamometer, it would interesting to *compare* the horsepower measurements using both of these techniques on the engine/s.
Awesome video, thank you! Question: why did you consider the weight you selected to be the equilibrium point? Is it because the engine could obviously not sustain its maximum RPM while under that load? I was expecting that you were going to see if tightening the screws would cause the motor to completely come to a haunt, and if not, then add more weight. And if I understand correctly, the clamp it’s the screws allows you to let the motto turn freely and you only tighten it enough to apply some friction to the shaft, but not so tight that the prony brake spins dangerously and uncontrollably? Trying to learn now how it works so I can perform some motor torque tests..
If you're looking for the article on wikipedia, it's called "de Prony brake" there, because the guy who invented it apparently had the family name "de Prony".
Good video. However I think it should be stressed that a prony break is only a rough estimation so I'm not sure if you can go down to 2 decimals. But still a great way to compare engines. Horsepower is of course a comparison unit, first derived to give farmers and other customers what they're buying (how many number of real horses).
I enjoyed this demonstration, it was very informative. Would it be possible to measure a four stroke engine HP. Keep up your educational information projects they are very interesting.
Tubal Cain, Great video as always! Why is it that one does not measure the rpm right at the time when the engine is slowed down under the load of the Prony brake to the point of equilibrium (instead of running free with no load -prior to applying the Prony load) for the purposes of the formula? I must be missing something here. BTW LOL! I love the reference to the "....busier than a one legged man trying to put out a forest fire". Got a big chuckle out of that.
Great mini series on this demonstration. I was worried that I would not see any of your excellent videos until fall. I do have one question though. It appeared that you would be able to add even more weight to the can because you were adjusting the nobs to allow some slipage. So by adding more weight into the can and also your formula, that would increase the torque which in effect would change the horsepower? Or are you not trying to find maximum hp and just see what it is capable of?
I really enjoy your videos. I am an industrial arts teacher. The boys in small engines are studying horsepower and brake horsepower. I think your videos are great for learning. Do you have one on a briggs and stratton engine being tested for horsepower? Thanks, Mr. Scott
I am curious.. this is not a criticism it's an honest question: Why not add one more ounce (an extra nut, maybe) to that Prony brake beam, so that the beam weighs in exactly at 1 pound. It would make your calculations that much more easy. Dimensions of the aluminum output hub (3") and the thickness of the brake beam (1.5") do not make any difference, as long as they are sufficient to put a proper working load on the engine at full throttle, is that correct? LENGTH of the beam is however critical, correct? Thank you. Excellent video set!!
You always have the most interesting posts! I look forward to seeing your videos in my subscription queue. I was wondering if you could do a video on setting cutting speeds for lathes and mills; that's an area that gives me trouble because I hate doing the math! I'm sure you have some old school shortcuts for that...
I'm confused. If you added a slightly lesser weight, but turned the clamp tighter, what would happen? Could you not find an equilibrium with a whole range of different weights, by tweaking the clamping force on the diameter? Then all those different weights would provide all different answers in the calculation. Does the heat being generated at the brake interface not need included in the calculation, or are these brakes just for getting a rough idea, and aren't expected to be as accurate as I am maybe expecting?
@zippy308 Yes--I might have been able to add a little more. It gets very touchy when you get to that point. Possibly could get 1 1/2 out of it. I'm still playing with it.
Thanks for sharing this! I plan on building an experimental steam motor and an improved steam turbine, and this will let me test the horsepower myself.
Excellent video! Let's see, it's holding 4.55 lbs at 31.5" (2.625'), so it's generating almost 12 ft/lbs of torque. Since hp = (torque * rpm) / 5252, that yields 1.08 hp. Not too far off from the Prony brake, and I'm sure it'd load down more at full throttle with a bit more weight. Not bad at all for an engine that old! Add to that all the kinetic energy stored in the flywheels, which is mind-staggering BTW, and you have an engine capable of doing some serious work! While sipping gas.
Shouldn't the calculation use the "under load" RPM once the brake arm and weight reach a balanced condition instead of the free RPM? If you don't, then you could tighten the two crankshaft bolts farther (more friction), which would then require more weight to reach a balanced condition, and you'd get a completely different horsepower number.
Nice demonstration! I love all your videos. I have one question regarding the RPM. In the formula, should you use the no-load RPM or the lower RPM that results from applying the Prony Brake as a load?
Love all the videos of yours that I have seen. I especially enjoy the explanations of why stuff works the way it does. In answer to the last post, does not the Proney brake add the load to the engine?
As i understand it really doesn´t matter much which type of wood you use (excerpt for it´s stability). What you want here, is to know exactly how much the engine can lift, at a set distance. If your wood has higher friction, you´d simply have to loosen the wingnuts to let it slide, and vice versa. You could use a metal-rod instead of wood as your weightarm, but the reason for the relatively thin woodstick, is that it´ll break if you loose control, and it swings all the way around. Was it made from metal, chances are that you´d have the engine dancing around...like a onelegged man, trying to stomp out a forestfire ;-)
I've always known what brake horsepower meant but never seen it demonstrated. Call me obsessive tho, but it bothers me that you didn't measure RPM under load. Not enough hands I guess.
I love your videos, however, you need to measure the RPM while the engine is under load. It noticeably dragged down when you applied the load. The free, unloaded RPM will give erroneous results of a higher HP than the engine is actually producing. EDIT: Oops, just saw that you took a measurement under load. Left my comment since I still needed to say that I like your videos. Great demonstrations.
