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small inertia dyno


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Glen
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Joined: 16 Jun 2004
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small inertia dyno

Heyo im thinking of knocking up a quick inertia dyno platform tommorow as im doing lots of pocket bike motor porting and such now for people,

the platform itself would be fairly easy to make and getting the flywheel or drum made and the MOI calculated fairly easily.

just curious about what you would need to read horsepower and torque. would i be right in assuming you can calculator torque from a known MOI and time to accellerate and from that derive HP?

all i really need to know is max torque, max horsepower, time to that maximum and at what maximum it occurs with not great accuracy. i just need to see differences.

thinking a hall effect sensor on the drum should basically be all i need to read this as theres some nice open source software that should calculate the time to accelerate and such after you input the given MOI.

ideas? thoughts? cheeers
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Post Wed Jul 02, 2008 6:31 pm 
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Fish_in_a_Barrel



Joined: 30 Sep 2006
Posts: 673
Location: Perth, Western Australia


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the trouble with that idea is the power graph of most motors is non linear, the way that most graphs are calculated is by fixing a motor to the drum and using different loads to plot a power graph. Then since the speed is known for each measurement the torque can be derived
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Post Wed Jul 02, 2008 6:36 pm 
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Knightrous
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The dyno i've used, has a pressure sensor on a calibrated pivot arm to calculate torque. I'll see if I can get some photos of it in the next few weeks to explain it for you.

Or you can have a look at how this guy built his
http://www.wotid.com/dyno/
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Post Wed Jul 02, 2008 7:11 pm 
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Spockie-Tech
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Joined: 31 May 2004
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Location: Melbourne, Australia


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Some more good info here
http://www.dynamometer-info.co.uk/advantages-of-each-type-of-dynamometer.htm

The prime difference between them is your either store the energy (inertia) and then allow it to gradually dissipate over a longer time than the acceleration run, or you have to radiate/dissipate it in real time.

For small engines, storing it is more achievable than for big engines. Building a flywheel that can store up the sustained output of a 500hp engine at full power over a period of 10 seconds or more without turning into a shrapnel bomb or a 300mph missile (drag car) is very difficult.

a 15hp donk is much more "absorbable" making inertia-storage practical - although you still want a nice scattershield around your flywheel. Imagine a 15hp motor spinner winding up over 15 seconds and how much polycarb you would want between you and it !

Its easier to radiate as well obiously, but then you have the feedback loop complexities (servo theory) to try and tune the "brake" to allow for acceleration at a controlled rate, but not *too* fast, when you dont know the output power beforehand.

How about building *both* into the one rig ? You could feed the output shaft to a disc brake first, then have a disconnectable coupling to your flywheel. If you want to run in Inertia mode, engage the flywheel coupling and disengage the brake pads, or vice versa. Its only one more sensor (a torque link) to run in brake mode. I dont know if anyone has actually done this, just an idea.. might get you the ability to tune and engine in both modes.

Remember that a lot of the cost of a Dyno is not just the power absorber. Its the whole "dyno-cell" room and surrounding systems. Controlled temp air inlet feed (no point testing if the dyno cell gets hotter after each run), Exhaust systems and noise proofing to muffle, fuel storage and feed systems, engne mounts to suit different engines and exhausts. Instrumentation, electricals, computers etc etc.. the power absorber is probably 5% of the overall cost
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Post Wed Jul 02, 2008 11:00 pm 
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DumHed
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Joined: 29 Jun 2004
Posts: 1219
Location: Sydney


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I've seen a good page years ago on how to build a go kart engine dyno.

A quick googling turned up a couple of potentials:

http://www.sportdevices.com/dyno/banco_kart.htm

http://www1.cedar-rapids.net/tdkmotor/MECHDYNO.HTM

http://www.angelfire.com/linux/dyno46/download.html
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Post Thu Jul 03, 2008 10:49 pm 
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