honda cbr 60rr cranckshaft moment of inertia

[federico_raceup]

Hi everybody,
I am Federico Scacco, member of the engine & drivetrain group of the race up team of Università of Padova(Italy).
I would be very grateful if somebody tells me the moment of inertia of the cranckshaft of the above mentioned engine. I don't know if somebody of you has measured the entire moment of inertia of the engine, in brief from the camshaft to the gearbox. Having this data or, in my contest, having its order of magnitude is the same because I need to use it in the design of the gearbox. So don't worry if your data is not the real one.
Thank you for the attention,
Federico Scacco

[tromoly]

If you have access to an engine dyno, you can perform tests to find the inertia of the entire system.

[federico_raceup]

This is the point: we don't have the possibility to access to an engine dyno unlikely. Of course, we use it once a year to develop the fuel map because it costs a lot. This is the reason why I asked this data to somebody having already measured it.
Thank you for the attention

[DougMilliken]

http://www.lmgtfy.com/?q=estimating+mass+moment+of+inertia

[SomeOldGuy]

Do you have access to the part to measure it?

[federico_raceup]

@SomeOldGuy
Yes we can access to every part of the engine but I realised that the most realistic data could be obtained with a direct measurement with the engine in neutral position. The idea is to measure the deceleration from a certain rpm to another, once you know the seconds neeeded to rpm to decrease you can calculate the angular deceleration and from these datas you can obtain the inertia if you know the resistance moment. The point is: how can I measure the resistance moment without the engine dyno? Of course the analytical way could be the solution... But I think it is quite difficult to consider all parameters.

[Menisk]

@SomeOldGuy
Yes we can access to every part of the engine but I realised that the most realistic data could be obtained with a direct measurement with the engine in neutral position. The idea is to measure the deceleration from a certain rpm to another, once you know the seconds neeeded to rpm to decrease you can calculate the angular deceleration and from these datas you can obtain the inertia if you know the resistance moment. The point is: how can I measure the resistance moment without the engine dyno? Of course the analytical way could be the solution... But I think it is quite difficult to consider all parameters.

Pull the spark plugs and run your starter. Monitor the amount of current it pulls and the voltage across it and make an estimate to the efficiency of the motor based on a bit of googling about DC motors. Knowing the amount of power to hold it at a measured RPM on the starter should give you some idea of your friction and then watching how quickly it falls back to stationary might give you some idea of inertia?

[Tim.Wright]

Estimating a moment of inertia is much easier than many people think. If you only need an order of magnitude accuracy there are 2 options:

1. For parts made of a single material (like a crankshaft) - make a very rough model in CAD, change the mass density until the mass is approximately what you expect and then extract the MOI.

2. For more complicated parts and/or assemblies, weigh or estimate the mass of the parts. Then estimate, by eye, the radius of gyration along the axes of interest. This radius of gyration must be smaller than the physical size of the part and is a distance you can "eyeball" by looking at the parts. I.e. for a complete motor the yaw radius of gyration could be in the range of 200mm. Then the MOI is calculated from your estimated radius of gyration squared multiplied by the measured/estimated mass.

Likewise, you can check any estimated (or CAD calculated) MOI values by converting them to a radius of gyration and verifying that this radius is smaller than the physical part. Otherwise there is an error somewhere.

[federico_raceup]

Thank you for having answered my question.
@Tim.Wright: I think that your idea is very good if you only need to have an order of magnitude accuracy, as you correctly said.
I would like to have a more rigorous data, so according to me the way suggested by Menisk best fits with my goals.
As soon as I try this experiment I'll tell you how I did it and the result obtained.

Thank you a lot,
Federico Scacco