# engine dyno using simpledyno!



## MCRIPPPer (Dec 13, 2014)

im working on a dyno project for measuring HP of 1/5 scale rc engine(23 through 31cc, about 3 to 5 HP).

found this handy computer program that uses audio input signal to read RPM. you put a magnet somewhere on a rotating part and put a coil next to the magnet (you can even just use an earbud as the coil).
https://sites.google.com/site/simpledyno/home

already tested the HP of one of my homemade air powered engines. it put out 70 milihorsepower! 

now that i have tested the software i am ready to start building the real dyno.

i think i will start with an engine dyno because its easy. them make a chassis dyno maybe.


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## stevehuckss396 (Dec 13, 2014)

Cool project. Will be following this one for sure.


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## MCRIPPPer (Dec 13, 2014)

later i will post pix of my model engine dyno, which is just a flywheel made of steel with a plastic magnet holder(didn't work when i put the magnet in the steel flywheel.) mounted right on the crankshaft, with an apple ipod earbud duct taped to the engine next to the magnet!

basically the software calculates your torque based on moment of inertia of flywheel and rate of change in rpm.


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## lohring (Dec 14, 2014)

That's called an inertial dyno and is a great way to measure the power of an internal combustion engine.  It's much easier to use than a brake dyno and gives results very quickly.  We've used one since 2003 to develop various engines.  You can use commercial data loggers and software, but the power and torque is calculated from the increase in rpm with time.  A simple, mouse based version can be found here.  An explanation of the physics with design information can be found here.  An article on our dyno (pictured below) is in Model Engine Builder, Issue 15.  

Lohring Miller


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## MCRIPPPer (Dec 14, 2014)

thats a very nice dyno. and it looks about the same as what i need to build. it looks like you have the flywheel directly coupled to the engine. i didnt want to do that because these engines can easily reach 20k rpm with no drag from air and drivetrain. im guessing you have not had any issues spinning your dyno up to high speeds.


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## lohring (Dec 15, 2014)

We've run our dyno to over 25,000 rpm and have tested 2 to 12 hp engines without problems.  A typical run starts at 12,000 rpm and goes to 18,000 rpm for a power peak at 15,000 rpm.  We probably have close to 1000 runs as an afternoon session consists of around 50 runs.  

There are two safety systems between the engine and flywheel.  The first is an RC car centrifugal clutch.  It allows idling and releases when the engine slows down after a run.  The second is a square key between the engine and the input shaft.  It allows for different engine mounts and acts like a fuse.  We once seized an engine at over 15,000 rpm.  The key twisted 180 degrees before the clutch released.  The flywheel probably made a few revolutions during this time as the engine was completely destroyed.

I was very concerned about flywheel strength with a 5" diameter flywheel, so I checked it with formulas from Machinery's Handbook.  Even though mild steel is probably safe, I used 4340 heat treated to Rockwell 35 C.  Since stresses are highest at the bore, we used Locktite with a snug, not a press fit, for the shaft.  The assembly was professionally balanced.  Holding the magnet in the flywheel was an issue.  We threw one through 1/2" drywall before we used screws plus JB Weld to hold it in.  In any case, never stand beside the flywheel.  A dragster style scatter blanket would probably be a good idea, though we don't use any scatter protection.  A steel shield would probably need to be very heavy to not add to the problem. 

The data logging system we bought has issues with noise at high rpm.  We've tried several rpm sensors without a perfect solution.  I would try a Hall effect sensor for a new build.

Engine noise is also an issue.  We always use hearing protection and have measured sound levels of over 110 dB beside the dyno.  It's surprising how much isn't only from the exhaust.  Warn your neighbors.  We run near some train tracks and are louder than the fast passenger trains.

Lohring Miller


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## scootdyno (Jan 24, 2022)

MCRIPPPer said:


> im working on a dyno project for measuring HP of 1/5 scale rc engine(23 through 31cc, about 3 to 5 HP).
> 
> found this handy computer program that uses audio input signal to read RPM. you put a magnet somewhere on a rotating part and put a coil next to the magnet (you can even just use an earbud as the coil).
> Google Sites
> ...


hello, Can someone please send me "Simpledyno" software, thank you. [email protected]


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