Schools & STEM

Learn motors, generators, rotation and force with low-cost 31YZ units

NuiCent can be used as a practical engineering case study for motors, generators, belt drives, rotational motion, measurement and energy accounting. The aim of this page is to make the physics easy to test rather than asking students to accept claims without measurements.

View the full NuiCent M4 invention page

Why 31YZ motors are useful for learning

31YZ classroom reference data

The current NuiCent 31YZ project uses the following reference values. Individual motors from different suppliers can vary, so students should verify the actual unit they have with a tachometer, multimeter and load test.

These values are NuiCent project references, not a guarantee of every 31YZ motor sold online. Supplier listings and measured results should take priority.

Centripetal force and the centrifugal effect

In a normal laboratory frame, a mass moving in a circle needs an inward centripetal force to continually change the direction of its velocity. In a frame rotating with the mass, the same situation is commonly described using an apparent outward centrifugal force.

This makes two important relationships easy to test:

• At the same mass and radius, doubling rotational speed gives four times the radial force.
• At the same mass and rotational speed, doubling radius gives twice the radial force.

Worked example: a four-motor group has about 0.64 kg of bare motor mass. At 60 rpm and a 1.0 m radius, the ideal radial-force calculation is about 25.3 N. At 120 rpm, the same example rises to about 101 N, four times higher.

2 kg mass at the current CAD radius: 60 vs 90 vs 120 rpm

Using the current CAD radial reference of approximately 205 mm from the centre of rotation, a 2 kg rotating mass gives a very clear three-speed comparison. The gravitational weight of a 2 kg mass is about 19.6 N.

The comparison is between force magnitudes. Gravity acts vertically while the centripetal force acts radially toward the rotation axis; in a rotating frame the corresponding centrifugal effect is described as outward. They are not automatically opposing forces unless the geometry places them on the same line.

70 cm, 100 cm and 130 cm diameter study — 700 and 1400 rpm

For this comparison the three sizes are diameters, not radii: 70 cm, 100 cm and 130 cm. Their radii are 0.35 m, 0.50 m and 0.65 m. To keep the comparison consistent, the table uses the bare mass of four 31YZ units, approximately 0.64 kg, treated as acting at the stated radius.

The radial-force equation is F = mω²r. Doubling speed from 700 to 1400 rpm makes the calculated force four times larger. The F × r column is a structural load-moment comparison only; radial force acts through the centre and is not by itself a driving torque.

These high-speed large-diameter values are calculation/CAD studies. They should not be recreated as exposed classroom machinery. Real assemblies are heavier than the 0.64 kg bare-motor model, so their actual loads would be higher.

12 V vs 24 V and the two generator ratios

The 31YZ classroom reference is about 12 V at 3500 rpm. The NuiCent development comparison uses approximately 4000 rpm and 8000 rpm as two 31YZ shaft-speed targets. Using simple proportional back-EMF as a first estimate gives about 13.7 V no-load at 4000 rpm and 27.4 V no-load at 8000 rpm. Loaded voltage will be lower.

For the existing 15 W per 31YZ / 240 W for sixteen design target, a 12 V system corresponds to about 1.25 A per unit / 20 A total. At 24 V, the same 240 W corresponds to about 0.625 A per unit / 10 A total. This is a useful lesson in P = V × I: doubling voltage does not automatically double power.

The 15 W per-unit and 240 W total values are design targets, not verified continuous generator ratings. A proper test records shaft RPM, loaded voltage, loaded current and temperature at the same time.

Six simple STEM investigations

1. RPM vs voltage: measure the same 31YZ at several safe voltages and plot shaft speed.
2. Generator voltage vs RPM: drive a 31YZ shaft at known speeds and record open-circuit voltage.
3. Generator under load: add a resistor or safe test load and measure voltage, current and electrical power.
4. Pulley ratio: compare driver and driven pulley sizes and predict shaft speed before measuring it.
5. Radius and radial force: use F = mω²r to compare different radii without needing a large high-speed physical rig.
6. Efficiency and energy accounting: measure mechanical/electrical input and electrical output at the same time and discuss losses from bearings, belts, winding resistance and heat.

How NuiCent fits into the lesson

The NuiCent M4 combines four-arm motion, rail-guided sliders, Positive Locks, two independent 3600 mm GT2 main loops and groups of 31YZ units. That makes it a useful case study for asking engineering questions such as:

• How much force is created by a chosen mass, speed and radius?
• How much belt travel is produced by slider movement?
• How do pulley ratios change 31YZ shaft speed?
• How much electrical power can a 31YZ produce at a measured RPM and load?
• How much mechanical power is required to obtain that electrical output?
• How do opposing clockwise and counter-clockwise rotating groups change reaction torque and vibration?

View the current STEP/STL/DXF + manual builder pack →

Energy conservation is part of the experiment

A 31YZ used as a generator converts mechanical energy at its shaft into electrical energy, with losses. Rotational motion and radial loading can transfer forces through the mechanism, but they do not remove the need to account for energy input, stored rotational energy and losses.

For a strong school experiment, measure input and output simultaneously and let students compare the result with their prediction. That makes NuiCent useful as a real engineering investigation rather than a demonstration with a predetermined conclusion.

School safety

NuiCent Schools & STEM

Motor • generator • belt drive • rotational dynamics • measurement • CAD • energy accounting

Back to The Invention