Stabilizing Industrial Lettuce Spinner
Most recent answer: 05/07/2015
- Adam (age 27)
Howard, CO, USA
Great question, and very clear!
Using a heavier metal basket, keeping the basic dimensions the same, won't reduce either the force or the torque that has to be exerted on the unbalanced load. Look at it this way. For a balanced basket, the net momentum is zero, so there's no change in momentum and no force needed other than whatever is needed to counteract gravity. There is an angular momentum as the basket spins, but it doesn't change so no torque is needed other than a bit to cancel the frictional torque. Now add some unbalanced lettuce. The changing force and torque needed to keep it spinning is the same regardless of the weight of the basket.
I've assumed here that the basket spins with very little wobble. If it's allowed to wobble off-axis a lot, then those wobbles would involve changing its momentum and its angular momentum, so they do involve changes in the force and the torque. That would make a harder physics problem to solve.
Mike W.
(published on 05/07/2015)
Follow-Up #1: force and displacement
- Adam (age 27)
Howard, CO, USA
Yes, we're in agreement. I considered the limit where the mounting held things very nearly in place. The mounting then has to supply changing forces and torques to do so. We agree that those changing forces and torques are the same regardless of the mass of the basket.
If the restoring forces are weak, allowing the basket to wobble a lot, then your argument is correct. A heavy basket will wobble a smaller distance to compensate for the unbalanced load, keeping the net momentum constant.
What sort of suspension will you use? Is the position allowed to wobble much? What about the angle of the axis?
Mike W.
(published on 05/09/2015)
Follow-Up #2: industrial lettuce spinner
- Adam (age 27)
Howard, CO, USA`
Hi Adam- I'm no expert in this stuff, but I don't think the heavier basket will help if there's just a small room for wobble. The reason is that if the wobble is mainly constrained by forces and torques, with only a little of the free wobble left, the magnitude of those forces and torques is not sensitive to the basket weight. It's only if you go toward the other limit of unconstrained wobble that the distances can be reduced significantly by using a heavy basket.
Here's a thought. If the motor is rigidly mounted to the spinning basket, you could let the whole combination wobble around held loosely in place by some springy supports. You can see right away that that would greatly reduce the changing forces exerted by the bearings on the axle. Using a heavy basket would then reduce the physical distances that the whole assembly would wobble. I guess if the spring supports also let the whole assembly (motor+axle+basket) twist around some, that the internal torques exerted by the bearings would also be reduced. I'm focusing on the forces and torques exerted by the bearings because that's where you'd expect damaging wear to occur.
Mike W.
p.s. DId you guys consider just using the spin cycle of a commercial washing machine? Does that question reval my extreme ignorance?
(published on 05/10/2015)