[martinw]

Dear all,

I apologise if this request is in the wrong place, but I would be very grateful for any replies.

A long time ago, ( yes, a long time ago) I read about a gizmo that you could have at home which was a small cylinder you placed on the table. The cylinder was taller than its diameter but about only eight inches tall.
You place the tube on the table, and lo and behold, after a minute or so, it topples over. You then place it upside down on the table, and it topples over again after a similar interval, and so it goes on...

If I remember correctly, there were no batteries involved, so there is some "hour glass" mechanical mechanism that puts some kind of internal mass outside the centre of gravity.

I am pretty sure that this was described in the Sunday Telegraph Magazine some time in the mid 1960s, but the mechanism was not. For all I know, they can be bought off the shelf today.

Any suggestions would be very much appreciated. Thank-you.

Best wishes,

Martin

[Geof]

If I remember correctly, there were no batteries involved, so there is some "hour glass" mechanical mechanism that puts some kind of internal mass outside the centre of gravity....Martin

The center of gravity is the point at which the mass appears to act; all the mass is outside the center of gravity, all the time.

To tip the cylinder either you have to move the center of gravity outside the area of the base (which is impossible), or you have to give a torque to the cylinder.

My guess is that inside the cylinder there is a rack mechanism running from end to end and across the diameter; something like a cog railway.

There is a flywheel geared to this rack with a very small gear.

When you stand the cylinder up the flywheel runs down the inclined rack spinning as it goes.

Because the gravitational potential energy is being turned into rotational kinetic energy via a small gear the flywheel only accelerates slowly.

Even though the flywheel falls down the rack slowly at the bottom all the gravitational PE has been converted into rotational KE and when the flywheel hits the bottom it is braked against the end of the cylinder.

This braking imparts a torque to the cylinder causing it to fall over.


I hope my description is understandable.

[martinw]

The center of gravity is the point at which the mass appears to act; all the mass is outside the center of gravity, all the time.

To tip the cylinder either you have to move the center of gravity outside the area of the base (which is impossible), or you have to give a torque to the cylinder.

My guess is that inside the cylinder there is a rack mechanism running from end to end and across the diameter; something like a cog railway.

There is a flywheel geared to this rack with a very small gear.

When you stand the cylinder up the flywheel runs down the inclined rack spinning as it goes.

Because the gravitational potential energy is being turned into rotational kinetic energy via a small gear the flywheel only accelerates slowly.

Even though the flywheel falls down the rack slowly at the bottom all the gravitational PE has been converted into rotational KE and when the flywheel hits the bottom it is braked against the end of the cylinder.

This braking imparts a torque to the cylinder causing it to fall over.


I hope my description is understandable.

Dear Geof,

A brilliant idea. But could the whole lateral force for toppling the tube not be accomplished otherwise? Say, you have a whole load of lead shot ( or whatever) stacked up vertically on one side of the tube (when viewed on plan) which you can suddenly release through a 90 degree bend which imparts a force laterally?

Not sure about the recovery mechanism BTW.

Best wishes,

Martin

[martinw]

On reflection, it is not lead shot, it is a lead weight with a hole in the middle that falls vertically and goes round a smooth 90 degree curve before whacking the side of the cylinder and imparting the "knock".

Well, it might work...

Best wishes,

Martin

[Geof]

On reflection, it is not lead shot, it is a lead weight with a hole in the middle that falls vertically and goes round a smooth 90 degree curve before whacking the side of the cylinder and imparting the "knock".

Well, it might work...

Best wishes,

Martin

You described it taking a minute or so but your lead weight free falling is going to get to the bottom in a fraction of a second; actually it would fall while you were turning the cylinder over. In addition it would whack the side at the bottom which is more likely to just bump the cylinder sideways rather than tip it over.

The time requirement is what makes me conclude it is a rotating mass; when a mass falling under the influence of gravity is constrained to rotate it falls slower than a non-rotating mass because some of the gravitational PE is converted into angular KE. Think about a Yoyo it falls much slower than a free falling non-rotating mass.

[holbieone]

http://www.physics.umd.edu/lecdem/se...osb1/b1-15.htm

[holbieone]

http://pirt.asu.edu/detail_1.asp?ID=247&offset=225

[martinw]

Dear holbieone,

Thanks for the links. There is a whole load of good stuff there.

Best wishes.

[martinw]

Dear Geof,

You could get whatever time delay you wanted by using some kind of ball release mechanism that is triggered by an hour-glass timer.

Best wishes,

Martin

[Geof]

Dear Geof,

You could get whatever time delay you wanted by using some kind of ball release mechanism that is triggered by an hour-glass timer.

Best wishes,

Martin

True, but I still think my system would work and it only has one moving part. Maybe I can get stimulated during the holiday season and make one to test it.