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Author Topic: Twist drive builds  (Read 476 times)


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Twist drive builds
« on: May 10, 2023, 03:12:26 AM »
                        Keep in mind, that you are going to be measuring
                            a very small distance of travel in these interactions.

Please bear with me here.  For some experienced builders, all this info
will be the obvious, maybe even bothersome to read.  Naturally so.

Just please make sure your replication (if a replication) is a replication of the
magnets used, magnet orientations, positions and motions, in the most detail you can.

This should come as something of a relief, for anyone doing a replication.

All that is required is precise measuring of the weight of each weight object
the precise measuring of  the distances of their rise / fall.  That's it.

My device was built to be versatile and it has much more travel distance available
on the SL than is needed.

A much simpler device could be used in the replications.

But lets talk those variations through before implementation ?
... ... ... ... ... ...
                                        Use brand new ceramic magnets,
                     that have never been in contact with rare earth magnets.

My method of increasing the precision of the fall measurements, was to
use indication dials which have very much larger diameters than do the pulleys.
... ... ... ... ... ...
There is NO need to use eccentric pulleys. (would not be a replication anyway).

The RO pulley should be about the same size as I used.
The pulley on the SL indicator MUST be the same size as the RO pulley.

The pulley used to translate the force of the falling of the SL weight object
from vertical to horizontal can be of what ever size is convenient.

All of my bearings have the grease / dust seals and grease removed. This makes them
much more sensitive to small forces (both the linear and round bearings).
I lubricate with a light oil.

The bushings for the SL indicator dial needle shaft, are hand made and do not contain
ball bearings.  These carry only very light forces any way.

The SL indicator dial and the RO indicator dial should be identical.

The RO and SL magnets should align perfectly edge to edge, up and down and
side to side when they meet.

The RO magnet must be exactly square to and centered upon the center of axis
of the shaft is rotates upon.

The SL unit magnet must slide in the same planes (left right, up down) as the RO axle
rotates upon.

The SL unit must be level.

Its guide rods should not give any twist to the  unit as it moves along them.

In my opinion, it best to use actual weight objects rather than a force gauge.
set up.  This eliminates contesting of the quality / precision / accuracy of the
gauge.  Some times, primitive is better / easier to verify.

The balance of the rotating unit should be demonstrable / demonstrated.

The sensitivity of the test units to force / weight should be demonstrable / demonstrated
                     (what is the minimum weight it takes to cause it to move).

In my opinion it is best to build such that the magnets are easily removed / substituted.

The magnets should be nearly matched in terms of their lifting capacities.
                                      (Buy extra magnet sets)
                                      see CITFTAS post below

My test bench is mostly wooden / does not interact with magnets. Even though there
are ferrous guide rails and so on, my test units displacements caused by the weight objects
are not measurably  affected by magnetic interaction with the ferrous components. No difference when the magnets are present or are not present.
            This would not be the case while using powerful rare earth magnets.

Even the ceramics can cause unwanted deflections between the two magnets. The test unit
needs to be rigid enough to handle the forces involved.  A little trial and error as your design
and build evolves, will be necessary.  Minimum mass, weight, friction, maximum rigidity.

Non magnetic railings won't be needed, given that railings are kept far enough off from
each side of the sliding magnet (no closer than 3 inches for these ceramic magnets).
                This would not be the case while using powerful rare earth magnets.

EXTEND the SLiding magnet fixture to beyond the rails.

Sliding rails should be no closer than 5 inches from the ROtating magnet.
               This would not be the case while using powerful rare earth magnets.

The accidental / undesired magnetization of shafts, sliding rails, and ball  bearings
is difficult to avoid, especially when using powerful magnets.  These events will adversely
effect measurements.

Rare earth magnets (believe it or not) do not behave precisely as do ceramic ones,
while interacting with each other.  However, it is still possible to get very similar results
while using those rather than the ceramic ones.

All fixtures must be many times more rigid, when using rare earth magnets, than
when using the less strong ceramic ones.

« Last Edit: May 10, 2023, 02:33:32 PM by Willy »


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Re: Twist drive builds
« Reply #1 on: May 10, 2023, 03:17:36 AM »
None of my ceramics were purchased on line.
On line some times gives more specs than does the packaging in
big box stores. 

In the U.S.

ACE hardware
Tractor supply
Home Depot

I have bought ceramics at each of these locations above.

Buy several extras sets.

      Just these magnet specs (either)  are a good start


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Re: Twist drive builds
« Reply #2 on: May 10, 2023, 03:19:56 AM »

Feel free to delete or move if you feel this doesn't belong here.

The easiest method I have found for checking the strength of a magnet is as follows.  In an area free from ferrous influence such as outdoors on a wooden table you place a yardstick.  Put a compass at the zero end of the yardstick with compass and yardstick oriented so that the yardstick is at a right angle to the north south needle of the compass.  Now starting at the opposite end of the yardstick with one pole pointed at the compass slowly move the magnet towards the compass.  When you see the compass needle start to move towards the magnet you need to write down how many inches from the compass you are.  You also need to number the magnets so you can keep them straight as you test.  If you have any doubts as to which pole of the magnet is which this will also tell you that as well as give you a relative strength in relation to the other magnets you test.  I hope this helps as I have seen pretty large variations in magnets I have tested.



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Re: Twist drive builds
« Reply #3 on: May 10, 2023, 04:48:59 PM »
There is a series of steps to follow in order to calibrate your twist drive
so that it will function as intended.

The weights of the weight objects that can be used will be specific to the
magnets you have installed.  How to determine this ?

The correct, far / maximum distance, of the sliding magnet from the rotating magnet
must be determined.  How to determine this ?

The optimal number of degrees of rotation of the rotating magnet, from 90 degrees off from
parallel to the sliding magnet must also be determined. How to determine this ?

Once a builder has completed his build and has a good feel for the magnet actions
involved, describing the calibration process will be easier to communicate /
easier for the builder to grasp.  Its pretty confusing otherwise.