Have bought myself a cheapo rowing machine, but the computer that comes with it is exceedingly crap (can't even measure strokes accurately!), so thought I'd have a bit of fun building a new one with a raspberry pi!
I'll be adding a new sensor on the flywheel (it only measure the cord being pulled at the minute), and using the maths in the link below to calculate the power, and from there to distance and calories etc etc. Now it's not going to be a concept2, but it'll be fun anyway! A pic of the flywheel is shown below, I've roughly measured it inside the machine.
http://eodg.atm.ox.ac.uk/user/dudhia/ro ... meter.html
I need to calculate the moment of inertia for the flywheel, this is the main number I need.
Following the links for moment of inertia on Wiki, I get a mass of about 22kg for a cylinder of 150mm radius, and 40mm height, and if I use the App.ActiveDocument.Pad.Shape.Volume in Python it matches what I get from the wiki volume calculation for a cylinder. For my flywheel, using App.ActiveDocument.Pad.Shape.Volume ends up giving me a mass of about 7.5 kg when multiplied by the density of iron, which seems pretty plausible.
The moment of inertia about the Z axis for that cylinder should be 0.250333884 kg m^2 if I've done my maths right. Now the issue: I can use App.ActiveDocument.Pad.Shape.MatrixOfInertia on the cylinder shape in Freecad, and the results are:
Code: Select all
Matrix ((1.62813e+10,3.23442e-09,2.08616e-07,0),(3.23442e-09,1.62813e+10,1.00576e-08,0),(2.08616e-07,1.00576e-08,3.18086e+10,0),(0,0,0,1))
http://www2.eng.cam.ac.uk/~hemh1/gyrosc ... ertia.html
I appreciate this is not technically a Freecad help issue, but maybe someone knows some clever way to get the figure directly?
Thanks!
Brutha