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Tractor Talk Discussion Forum

Prony/pony brakes

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JT

12-08-2004 07:20:51




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Does any one know how to build a Prony/Pony brake for tractors. I have seen a lot of them at tractor shows, thought they were kinda neat, I would like to build one for a toy. Does anyone know what the dimensions of the paddles should be and and how far off center. I am looking to build a small one to put on gas engines, small engines, hit n miss engines and maybe some small tractors.




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Jerry/MT

12-08-2004 21:11:22




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 Re: Prony/pony brakes in reply to JT , 12-08-2004 07:20:51  
A Prony brak consists of a brake band that clamps on a spinning shaft. Connected to the brake band is a lever arm that reacts against a spring scale or a load cell. The shaft is set spinning and the brake band is clamped down till the shaft just begins to slow down. The force is measured at that point as is the rpm and the horsepower is calculated by : HP = rpm x lever arm length x measured force/5252. Needless to say, the answer you get is not too precise.

I don't understand how you can get power and torque information from the Baker Fan without a calibration based on measured dimensions, air density, rpm, Reynolds No., etc. You can ceratinly load a shaft with the device but what's the load?

buickanddeere suggests a more precise method for determining power directly and toruqe via : Torque = HP x 5252/rpm.

My two cents.

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JT

12-09-2004 06:28:53




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 Re: Prony/pony brakes in reply to Jerry/MT, 12-08-2004 21:11:22  
Jerry,
Do you know where I might find any pictures or anything of one of these. What I started looking for, I misquoted, I was looking to build a baker fan to run my gas engines with. I have now been enlightened of my lack of knowledge. :>)
But this Prony brac sound slike an interesting thing to build also. I am not looking for something to measure horsepower, I am not smart enough to run and calibrate something with accuracy, I just want soemthing to run my engines and tractors on for fun. I did find an old silage blower here a while back that I am going to belt up to some of my engines and see if they can pull it. It should give them a good workout.
Jim

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Jerry/MT

12-09-2004 14:38:40




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 Re: Prony/pony brakes in reply to JT, 12-09-2004 06:28:53  
You might try to locate some old physics books or old engineering books to find a picture of one of these. Try a web search also.
If you really want to just run something for fun, the Baker Fan is a better deal than a Prony brake, in my opinion. It takes a bit of technique to use a Prony brake whereas the Baker Fan is just a hook up to a PTO or to a belt drive.



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buickanddeere

12-08-2004 12:22:11




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 Re: Prony/pony brakes in reply to JT , 12-08-2004 07:20:51  
Some collectors are going to a 50KW or occasionaly a 60 KW 540 rpm standby generator for a "load". They take about 75HP and 90HP to drive at full output. The generator is connected to a couple of old forced air electric furnaces got for free off the scrap pile. No cooling water hose required either and no hydraulics to leak. The power output is easily caluclated as volts x amps = watts and divide by 746 to get HP. And the generator comes in handy when ever the utility power goes off.

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Bob

12-08-2004 07:49:39




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 Re: Prony/pony brakes in reply to JT , 12-08-2004 07:20:51  
The correct name is PRONY brake, after the inventor.

However, when you mention "paddles" it sounds like you are talking about a Baker Fan rather than a Prony brake.

Hopefully, someone has some construction details!

Here's a link to a photo of a Baker Fan:



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Jerry/MT

12-08-2004 20:14:15




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 Re: Prony/pony brakes in reply to Bob, 12-08-2004 07:49:39  
How did you callibrate this so you could determine the power or toque?



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JT

12-08-2004 13:31:50




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 Re: Prony/pony brakes in reply to Bob, 12-08-2004 07:49:39  
Yep, that was what I was thinking of. I just want to make a small one for gas engine. Some of us type faster than out little minds can work.



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Joe Evans

12-08-2004 13:42:15




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 Re: Prony/pony brakes in reply to JT, 12-08-2004 13:31:50  
Here's another look at a Baker Fan.



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JT

12-08-2004 13:56:13




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 Re: Prony/pony brakes in reply to Joe Evans, 12-08-2004 13:42:15  
Joe,
What is the size of this and what size tractors doe you use on it? I do not want to make this thing so big that nothing can turn it. thnaks
Jim



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Joe Evans

12-08-2004 14:53:31




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 Re: Prony/pony brakes in reply to JT, 12-08-2004 13:56:13  
My brother measured the dimensions of that beast at one time, but I don't have those figures with me.

Estimation is 60" major diameter, 24" minor diameter, and the paddles are roughly 18" square.

This fan is reportedly rated for 100 HP, that is to say that it will load down a tractor or steam traction engine enough to allow them to develop 100 HP.

This thing will flat bury any tractor we've belted to it. Of course, the only way to drive it is by way of the belt pulley, so modern tractor with hi HP ratings don't get hooked to it.

For a small tractor test...geez I don't know what the dimension should be.

Food for thought: using Basic Fan Laws, if you want to double the RPM of the fan, 8x the HP is required. Say, if 10 HP will get you 150 fan RPM, you need 80 HP to get 300 RPM.

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JT

12-08-2004 15:00:19




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 Re: Prony/pony brakes in reply to Joe Evans, 12-08-2004 14:53:31  
Do you reckin that if I built it 20" diameter outside and 10" inside with 10" square blades would be too much? I want to put this on my Farmall M, B, and my McCormick Deering gas engines. nothin scientific, but just something different.



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Joe Evans

12-08-2004 20:28:46




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 Re: Prony/pony brakes in reply to JT, 12-08-2004 15:00:19  
No,no! Way too small!

If my math is correct, the swept volume of our Fan is 24.7 cubic feet. Your proposed dimensions only yield .57 cubic feet or about 2% of our fan's volume. Your M wouldn't even notice this load.

I would suggest as a starting point a fan with a major diameter of 48" and 16" paddles. This will yield a swept volume of 14.8 cubic feet. If nothing more than a 50 HP tractor is belted to it, this should work pretty good I would think. You can dink around with pulley sizes to get the M running the fan at its rated pulley RPM whatever that is. Two pulleys are better than one. A very large pulley on the other end would let your small stationaries get a good work out.

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JT

12-09-2004 06:23:08




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 Re: Prony/pony brakes in reply to Joe Evans, 12-08-2004 20:28:46  
Joe,
I appreciate all the input you have givin me on this. I never did really understand how they work and such, but, they were alwasy kinda neat to watch them belt an old tractor to them and them listen to her belller. I have quite a few engines from Briggs 1.5hp to McCormick Deering LB
3-5. so a big pully on one end and a small one on other end would be a nice way to go.
Now,for another question, how do you have the shaft supported, is it in a steel clamp with grease cups or is it running in pillow block bearing?
Jim

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Joe Evans

12-09-2004 06:37:41




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 Re: Prony/pony brakes in reply to JT, 12-09-2004 06:23:08  
It is supported in pillow block bearings.



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