Academy Pendulum Sales

Troubleshooting the Mark 2 Foucault Pendulum
(Model produced from 1/2005 )

The Mark 2 pendulum is a fairly simple device. However, there are some details that may have been overlooked or taken for granted during the initial setup. There is also the possibility that after several years of operation some changes may have occurred with the adjustments.

The most frequent problem is the variation in speed of the precession mode, or stopping in one part of the circle. Other problems such as a clunking sound at the top of the pendulum, or a pendulum that slows down and then stops may be encountered.

In most cases the main problems are generally within the adjustments.

Pendulum control adjustments:
Start the ball swinging and turn on the power, meter and tone switches.
A tone will sound whenever the ball passes the center of the pit (as power is then applied to the magnet). The Time Control should be set to turn the magnet off after the ball has reached its maximum swing and has started back. A fine adjustment of the Time Control should be made to obtain the smoothest cable operation at the top of the cable. Turn off the tone switch when done.

The Amplitude Control should be adjusted to obtain the swing distance desired. Be sure the swing is far enough for the armature O’rings to contact the magnet. Allow 10 min. between adjustments for the ball to respond.
When the adjustments are completed turn off the meter and tone switches.

Pendulum swing gets shorter and shorter then stops.
Check the control panel first to see if there is power to the panel.
Make sure the panel is on. Turn on the meter, & the tone switches. Check to see if the unit is triggering with each swing. The meter should deflect, and the tone should be heard each time the pendulum passes the center of the pit.
It is important for the armature O’rings to contact the magnet at the end of each swing. Failure to make contact will cause the pendulum to slow and eventually come to a stop. To increase the swing, turn up the Amplitude Control.  Allow several min. for the swing to pick up and stabilize.

If the control panel shows it is not triggering on each swing, check the logic panel for the following:
Try turning up the sensitivity control on the CM5 logic module. The sensitivity control is a 40-turn pot. Make several turns in each direction, but count the turns so you can return to the original setting if no remedy has been achieved.
Check to see that both photo beams are working. First cover one beam and pass your hand in front of the other pair of beams while you watch the indicator lights on the CM5 module. Repeat this process with the opposite pair of beams. Change the sensitivity control or replace any beams that fail.

Check to see if the Armature is centered in the magnet. Use the supplied centering gauge or an inside caliper to measure the distance from the armature to the top of the magnet bore in all directions. This adjustment is made using the leveling bolts to shift the tower.

Make sure the armature height is centered up and down within the magnet. Pull the cable sleeve to one side, and check to see if the bottom of the armature is even with the bottom of the magnet.  If adjustment is needed first check to see if the collets on the cable sleeve were not tight by pushing down on the armature. It should not slide on the cable.

Height adjustment
may be accomplished by either raising or lowering the cable using the height adjustment bolt located at the top of the tower, or by loosening the collets at the end of the cable sleeve and sliding it up or down. When finished, check for tightness by pushing down on the armature.

Never adjust the photo beam holders, as they were pre-adjusted prior to delivery.

Adjusting the photo beams:

With the ball stopped, remove one of the photo beams from the holder.
Using the ¼” drill rod supplied, or a straight ¼” rod approximately 9” long. Make sure the beams are aligned to the center of the cable sleeve. Insert the rod through one holder moving it as close to the cable sleeve as possible. The rod should point to the center of the cable sleeve. If it is off center even slightly use the leveling screws and mounting bolts to move the tower to center the photo beam on the cable sleeve.
Repeat this process with all four beams. Next move the cable to one side and slide the rod through one beam holder across the center to the other holder. They should line up.

#2 Clunking sound in the towel:

Check to see if the Time Control is set correctly.
Check the cable at the pivot point for fraying.
Check for damaged O’rings or armature height adjustment.
Adjust the armature height as described in the previous section.
If the O’rings are damaged or missing they will need to be replaced.
This will require removing the ball from the cable.

#3. Encountering variations in speed, or stopping at one point of precession.

The usual cure for this is in the photo beam adjustments, or by slightly raising or lowering the armature. Before adjusting the height mark the face of the cable Height-adjusting bolt for reference. Use the Height-adjusting bolt making the adjustments in 1/2 or 1/3 turn increments. If it begins to make a clunking sound you have gone to far. Reverse your direction and re-center the armature with the height adjustment bolt or by moving the cable sleeve as described in the previous sections.

Changing the cable on your Mark 2
Foucault Pendulum 

Replacing a damaged cable and/or O’rings:
Order new cable from Academy Pendulum Sales or, use a 1/8” 7x19 galvanized cable. The ends must be heat fused using an acetylene torch. Do not add rod or materials to the weld. Grind to size.
O’ring part numbers: #334 –2 req.  #314 – 3 req.
1. Turn the power off at the control panel.
Caution!  Whenever the weight is removed from the cable there is a danger of the cable winding up or spinning.  Keep clear of the cable during this process.
2. Position the ball cradle under the ball and slowly take the weight off the cable by lifting and locking the legs upright.
3. Remove the lower ball cap by unscrewing it.
4. Slightly loosen the top cap leaving it in place for now.
5. Loosen the set screws in the lower cable anchor at the bottom of the ball, and remove the anchor, and pull the cable up through the ball and end cap if possible. If the cable will not pull through, cut the cable above the ball using a proper cable cutter to expose a clean end on the cable, which can then be pulled through the ball. A new cable (with welded ends) will need to be installed.
6. Loosen the cable sleeve collets until the safety plate slides down and sit on the magnet.
7. Remove the upper cable anchor, and loosen the top clamping collet (above the height adjusting bolt).
8. Remove the cable by pulling it down through the pivot. Lift the cable sleeve and armature assembly out of the tower, and pull the cable up and out of the tower. Pull the cable through the cable sleeve. Avoid pulling any bad parts of a cable through the tight fitting parts.
9. Install 2 new O’rings part (#331) on the armature, and 3 new O’rings Part (#314) on the lower collet hub.
10. Pull the new cable up through the cable sleeve. This may require removal of the collets. Be sure to route the cable through these items in the proper order. Install the cable sleeve and armature back into the tower and let it rest on the safety plate. Next push the cable up through the pivot, and the clamping collet. Remove the collet if necessary to route the cable.
11. Install the upper cable anchor near the tip of the cable and snug the set- screw to hold the cable in place.
12, Lower the cable down to the ball. Remove the upper ball cap, and run the cable down through the cap, and the ball. Screw the upper ball cap back into place. Fasten the anchor about 2” from the end of the cable and secure the screws firmly. Screw the lower cap onto the ball.
13. From the top of the tower, pull the cable anchor up removing all the slack in the cable. Tighten the clamping collet, and move the cable anchor down until it sits on top of the collet. Secure the anchor set screws firmly.
14. Lower the ball cradle legs slowly and let the cable take up the weight.
Once the ball is hanging free it will begin to spin. Stop the ball occasionally, but let it spin until it reaches a neutral position and comes to rest. Remove the cradle.
15. Adjust the cable sleeve upward until it is centered in the magnet, and the O’rings on the lower collet are aligned with the center of the mounting ring. Tighten the cable sleeve collets. Test the collets hold by pushing down on the armature. It should not slide down on the cable.
Use the cable height-adjusting bolt to complete the centering of the armature if needed.
This should complete the installation.

CP 6/8/2011

  A devise looking like a toilet seat with legs and handles. The front legs fold up.

Photo courtesy of Hunt Oil, Dallas, Texas (ball designed especially for Hunt Oil.)
To view a typical Academy Pendulum Sales brass ball, click here.

Academy pendulum kits include:

  • A 235-pound 15” polished brass ball with sculptured end caps.
  • A 1/8” cable to suspend the ball.
  • One magnetic drive system is used to keep the ball swinging continuously. (The magnet is located near the suspension point at the top of the cable.)
  • One support tower and pivot assembly
  • One electronics control package
  • One 10”w x 14”h, educational brass wall plaque mounted on a walnut base. It includes a credit to Jean Foucault for his contribution to science, and a brief explanation of the pendulum.
  • Kit comes packed in wooden crates and weighs approximately 640lbs. total.