I am thinking about doing an experiment of spinning a wheel for a long time, like 8hrs+ before it stops due to friction. More specifically, I would like to reproduce this experiment published on YouTube: (cannot post links, but here is the id: EcYFBvO7cZI) , but with some modifications: the wheel will be positioned not horizontally, but at a 45 degrees angle. For this, it needs to be magnetically supported at both ends.
Basically, I need the following materials:
flywheel made of wood with outer metal band
flywheel axle terminated with metallic spheres
wooden frame
metallic spheres attached to the wooden frame with screws
permanent magnets for keeping the metallic spheres together
Do you think this is achievable using the technology available at VHS? And if not, what should be the best way of acquiring or building the necessary components?
I would really appreciate any guidance or advice you can provide about this project.
That project’s definitely achievable with the tools we have at VHS. Where you’ll likely have great problems however is your change to have both ends of the flywheel supported, as the key to the original design is that it’s a single point contact which gives almost 0 friction.
Thank you for your reply and for bumping up my posting privileges!
You are right having two points of contact instead of a single one could cause some issues. However, I don’t think the loss of efficiency will be very dramatic, as each one of them will carry only half the weight, which could even reduce the friction.
It is good news something like this can be achieved with VHS technology. I am quite excited receiving my membership and actually starting the work on the implementation!
Suspending at a 45 degree angle IS going to make this harder. You’ll have constant lateral load due to gravity, and you’ll also get some very strange forces you’ll encounter as the earth rotates under your flywheel, and the earth around the sun. Flywheels like to stay oriented in one plane, they don’t care about silly things like planetary motion.
The gyroscopic precession forces are pretty small and I am not especially worried about them. I have derived this formula for the precession force F of a wheel with moment of inertia I, spin angular velocity w, axle of length R, making an angle alpha to the precession axis, when T is the precession period:
F = 2 * pi * I * w * sin(alpha) / (T * R)
This riches its maximum when alpha = pi / 2, that is when spinning at a right angle to the precession axis.
Now if we assume these measures:
axle length R = 40 cm
spin frequency f = 10 Hz
flywheel mass m = 18 kg concentrated into its outer rim
flywheel radius r = 20 cm
T = 24 hrs = 86400 sec for the precession due to the Earth rotation around its own axis,
we get:
inertia moment I = mrr = 0.72 kgmm
angular velocity w = 2 * pi * f = 62.83 rad/sec
precession force = 2 * 3.14 * 0.72 * 62.83 / (86400 * 0.4) = 0.00822 N, that is about 0.005% of the gravity pull on the wheel!
Personally, I am not worried about this force and I think it can be easily counter-acted by the magnetic pull on the axle end.
The reason why this is so small is the magnitude of the precession period T = 24 hrs = 86400 sec.
The other planetary movements we can think about have even greater periods and lead to even more negligible figures:
rotation of the earth around the baricenter of the earth - moon system with about 30 days period
rotation of the earth around the sun with 365 days period
I hope I am getting these formulas right, but please let me know if you notice any mistakes.