Class Notes, 15 Feb, 2022

Note: Office hours on Tuesday, no Thursday

Intro to Electricity and Power

Start with example using light and power

100w incandescent bulb

23w LED bulb

120v 20a electrical circuit

wattage — what does it really mean?  Is a 100W incandescent bulb brighter than a 23W LED?

Compute amps based on wattage and 120v power.

Same brightness but different amounts of power, meaning LEDs are more efficient:

100W incandescent bulb ~1A

24W LED bulb ~0.2A


How things move

Think about power in the physical world:

voltage => weight

amps => speed

I weigh 85 kilos, how “dangerous” am I if I bump in to you while I’m walking?  While I’m running?

Is voltage dangerous or is amperage dangerous?

Bicycles vs. cars. Hit by a car or a bike at 10mph, which is worse? Is it really voltage or amps?

Handheld 50 KW stun gun.  500 times as strong as strong as a 100W light bulb.  Why doesn’t it kill people?

Think about volts vs. amps.  Where does the power come from?

Mine uses two 9V batteries, the ones you use in consumer electronics.   50KW is more like 50KV at 1 Amp, or 100Kv at 0.5 Amps.

Where we get power

A/C wall power to drive power supplies (PSUs).

DC power from a PSU, from 5V to 12V, we use 6V in class.

USB power converted by Arduinos or other devices

Arduino pins only have a tiny amount of power: 5V at 20 mA (milliamp).

How motors work

How to determine power requirements

How to drive servos vs. DC motors

Spring-loaded solenoids that require constant power to stay open/closed

How do you lock a motor and prevent it from turning?

What happens if you spin a DC motor?  It’s now a DC generator and could fry your Arduino.  We “fix” this using diodes in the circuits.

For moving things, use basic physics

  • gears — FAQ on 3d printing gears
  • levers — drive a lever with a solenoid, transfer short movement to long
  • pulleys – drive with DC motors or stepper

A great guide for animated mechanisms:

Reading/Watching Assignment

“The Secret Life of” was a British TV series by Tim Hunkin.  He now has a Youtube channel and a new series, “The Secret Life of Components“.  Each of the eight episodes is about 45 minutes long.  Pick the one you know the least about, watch it, and post comments here or in Looking Outward






One thought on “Class Notes, 15 Feb, 2022”

  1. So, I watched these all when they were first released. I went back to see where I learned the most, and it was the first podcast on chains. I’ve used chains for decades on bicycles, motorcycles, 3d printers, and machine tools, but it was basically “cut and paste”. I’d never really thought about using them in my own, new designs.
    Before watching this podcast I’d have just used string-and-pulley mechanisms and hoped for the best. Now I can see where using a chain, sprockets, and motors, would make for a much more controlled interaction.

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