Animation Fundamentals: Limit Switches

Limit switches can be important or, in some cases, vital to the operation of an animated device. As their name implies, they limit the range of motion to whatever is safe for a particular application. Most of the time they're used with linear motion drives, which would otherwise jam or break if not stopped at each end of travel. But they're also useful for limiting rotary motion when it's not fully reciprocating; a practical example is shown.

Typical Configuration

Practical Application — Linear Drive

This mechanism operates the firehouse doors.

Practical Application — Rotary Drive

The large black gear in the middle rotates only just so far; the elongated W-shaped brass rod attached to it engages the two limit switches at the bottom to stop the motor. (This is just one part of the excavator mechanism; the two other limit switches are parts of other functions.)

Wiring

Since the motors are DC, it's easy to wire limit switches with just a couple of diodes, and a DPDT switch to control the mechanism.

Any one of many diodes types can be used, assuming it can handle the load. The most common are 1N4004; they're cheap, plentiful, and rated to handle most any modeling application. Microswitches are available in abundance, as are DPDT switches.

Examples

Also See...

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