Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
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 _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
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