Troubleshooting Tips:
Measuring Time
Magnets and Motors
How Do I open the Box?
Measuring Time
The clock escapement that is assembled in Lesson 13 of the Measuring Time unit is one of the most exciting activities in the entire STC program. Because it is a fairly complex mechanical device, a number of adjustments may be necessary to get it to work. If your students get stuck troubleshooting the escapement and really need help, here are some things they can check.
Have the correct parts been used? It is especially common to switch bushings
and end caps. Switching parts may produce combinations that do not work.
Are the parts assembled in their specified positions? For example, the toothed wheel should be in front of the pallet arm. Compare the assembly of the pallet arm and pendulum to the diagram at the lower left of page 56 in the Student Activity Book, and check the angles of the rods. Have the parts been mounted correctly on the base? There should be a hole in the base between the two posts, between the two blue rods, and between each adjacent blue rod and post. See step 1 on page 55 of the Student Activity Book.
The weight (bottle of water) should rotate the toothed wheel in a counter-clockwise direction as the string unwinds. See step 8 on page 56 of the Student Activity Book. If the toothed wheel rotates clockwise, unwind the string that supports the weight and rewind it in the opposite direction.
Check the swing of the pendulum. It may be hitting the base, the pallet arm, a table leg, or etc. This is probably the most common of all problems. Adjust the parts as necessary so the pendulum will swing freely.
If the toothed wheel does not seem to be pushing the pendulum with sufficient force to keep it swinging, there may be excess friction in the escapement. Check to see if the tape used to attach the string to the lower purple rod is touching a bearing or has entered a hole in a bearing. Again, refer to step 8 on page 56 of the Student Activity Book. If this checks out, next try to wiggle the upper and lower purple rods to be certain that they can rotate freely. It may be necessary to partially disassemble the escapement to correct this problem. If the toothed wheel still does not seem to be rotating with enough force, there may not be enough weight to drive the escapement. In this case, add more water to the bottle and try again.
If after a few swings of the pendulum, the clothespins on the pendulum and the pallet are pushed aside, the toothed wheel may be rotating with too much force. To correct this, empty some water from the bottle, and try again. This problem can also occur if the clothespins are not gripping the rods with sufficient force. If this is the problem, remove the clothespins, put some masking tape around the rods, and replace the clothespins.
Finally, check that all parts are securely assembled. Parts may have worked loose, especially if the unit has been used repeatedly.
If it still doesn't work, it may be best to completely disassemble the escapement and start over.
Magnets and Motors
In Lessons 9 and 10 of Magnets and Motors, students plan and execute an experiment to test the strength of electromagnets. After hearing that at least one customer had found the language a little misleading in regards to the possible effects of altering the different variables (diameter of magnet's core, number of coils, number of batteries, etc.), the NSRC suggested a few changes in the wording, which we effected in a recent reprint of the teacher's guide.
When I conducted the activities, I noted several troubleshooting tips that might help. For one thing, it is important to conduct these trials multiple times (as with most trials). Multiple trials will help eliminate the effects of "uncontrollable" variables such as jinxed grabs of the paper clip by the magnet or clumsy hooking of the washers by fingers (I found it best to add washers to the unattached paper clip and pick it up again with the magnet after each addition).
Also, there are a couple of factors that may mask some of the effects
that altering the variables actually can have on the strength of the magnets:
the strength of the batteries and the weight of the washers used in the
experiments. The strength of the batteries can be augmented only by using
more of them or by replacing weak ones more often. The weights used offer
more possibilities. I tried using the brass washers that go with paper-fastening
brads (these washers 
weigh less than the steel
washers included in the unit), and I got more easily measurable differences
from several of the electromagnets. These washers worked well for me because
they functioned as smaller units without being so small that the magnets
would hold inconveniently large numbers of them. If your batteries are brand
new, though, or if you're using several, the brass washers may be too lightweight
to be appropriate units. Let us know whether you've ever run into a problem
with this section and how you dealt with it. We may end up changing some
materials in the unit if that seems called for.
How Do I Open the Box?
Lately, this has been a frequent question. We now use two black plastic plugs to lock each unit we ship. Contrary to popular belief, these plugs are easy to remove. Simply slide a key or the blade of a screwdriver into the slot under the head of the plug and rotate. The head pops up, and the plug can be removed. Don't throw it away. To reuse it, simply close the lid, reinsert a plug into each hole, and mash the head down to lock it.