Web Research
General Info
Make an eddy-current http://www.eddycurrentbrake.com/ECBrake/Project.html
using electric motor http://www.ls1tech.com/forums/dynamometer-results-comparisons/150901-how-build-you-own-dyno.html
more home made eddy-current brakes http://www.rollaclub.com/board/topic/21719-diy-engine-dyno/
Calculation spreadsheet from dtec http://dtec.net.au/Downloads/Inertia%20Dyno%20Design%20Tool%20Ver2.xls
DIY Dynos
forum with some more clues on second hand eddy current thangs http://www.eng-tips.com/viewthread.cfm?qid=84432&page=58
Parts Suppliers
http://www.land-and-sea.com/eddy-current-dynamometer/eddy-current-dynamometer-specifications.htm
http://www.industrialbrake.com.au/driveline_retarders.htm#tech found the use of the word retarder instead of brake got different matches - truck parts western australia
dynojet - specs of the 200i indicating it has no eddy curent brake, just inertia. Note that eddy current braking is an option. Need to see if it is an easy option for older models such as the 150 http://www.dynojet.com/catalogs/2009_Powersports_Catalog.pdf
Forum Tidbits
Info On Old DynoJet Machines
http://www.powercommander.com/downloads/DynoManuals/idynowiring.02.pdf this is a wiring schematic for recent model 200i
installation for add-on eddy current brake. Must check whether this is possible on a 150 model (said to have been upgraded to 200, whatever that means) http://www.powercommander.com/downloads/DynoManuals/98100007.01.pdf
Add on eddy current brake kits http://www.dynostar.com/pdf/duk500en.pdf
Info on the Dynojet fudge factor and how to get true HP http://www.factorypro.com/dyno/true1.html
Why the fudge factor exists is in The Story Behind the Dynojet Chassis Dyno - The Truth Meter and it's to guess at crank power (though who cares about crank power when it's the wheel power which is the final force you need to know)
"Dynojet's final number-fudge was arbitrarily based on a number from the most powerful road-going motorcycle of the time, the '85 1,200cc Yamaha VMax. The VMax had 145 advertised factory horsepower, which was far above the raw 90hp number spit out by the formula. Meanwhile, existing aftermarket torque-cell engine dynamometers delivered numbers that clustered around 120. Always a pragmatist, Dobeck finally ordered his Chief Engineer to doctor the math so that the Dynojet 100 measured 120 hp for a stock VMax. And that was that: For once and forever, the power of everything else in the world would be relative to the '85 Yamaha VMax and a fudged imaginary number."
Outside the Box?
Some ideas that are outside the norm:
electric trailer brakes - won't be accurate but they come with controllers and should be able hold steady rpms with a feedback loop. We'd be looking at about $300-500 for a simple drum unit, as they are designed to stop 1000Kg+ trailer, they should not have any overheating issues for short runs
regenerative brakes from the new electric cars/bikes tech - I am finding out more info (waiting on response). For around $1200-2000 you get a ~20Kg electric motor kit with braking capability
No roller - just hook something straight to the hub nuts? Our wheels are standard sizes, why not have a unit that can be attached to the scooter lift and bolted to the hub using the wheel nuts. It would be the most common usage scenario (using the above electric motor would also act as el-start.