Control of dc motors is based on ideas from the 19th century. The device pictured is a double-pole, double-throw “knife” switch, made somewhat famous by its appearances in several movie re-creations of Dr. Frankenstein’s laboratory.
An FRC speed controller is just a switch like this, improved so that it can be thrown back and forth very rapidly without wearing out, heating up, taking up a lot of space, or requiring much effort.
Just to clarify, I think the idea of building macro-scale demonstration pieces is great. What bugs me is the utter lack of insulation on pretty much everything (seriously, it’d be almost impossible to touch the actual ‘switch’ part of this assembly without shocking yourself).
Hah, was wondering if anyone would recognize it, though to be honest it wasn’t my favorite math text. It wasn’t bad, but a lot of the early point set proofs which ought to have been done in rigor consisted of just pictures and handwaving (claiming “we can construct a homeomorphism” but never actually demonstrating one, etc).
I still keep it around, though, for want of any other good references for point-set topology.
It is a perfect example. In reality, an H-Bridge is just transistors performing the same operation, just solid-state.
I guess the spark could be a possible recruiting tool – that, only if the correct precautions are taken! It’s not the best idea to try this at home, at least if the voltage is greater (or lower) than 0v
I think that that is actually quite a typical setup to introduce the system.
However, it’s pretty cool how I still use that setup all the time. Just take a DPDT switch. Connect the middle pins to the motor. Connect one side of the switch to the battery. Connect the other side to the battery too. However, on the second side, reverse the polarity. If the switch is on one side, the motor will spin in one direction. Switch the switch and the motor will switch directions!
I am wondering what that was even meant for. Is that supposed to be a motor tester of some sort? It seems quite dangerous!
Not exactly an H bridge since the legs are not independent. However, please add a fuse or breaker to this in the future. Not the 120 amp either, it must be safely sized for the smallest wire.
While it is unlikely to cause any harm at 12 volts, this is a good demo to show what was considered “safe” 100 or more years ago. I am reminded that when the IBEW was founded in 1891, the average life expectancy of a line worker was 36. It was common practice at that time to string power cables on poles that contained live wire using horse drawn wagons with ladders mounted on them.
To use this for household line voltage please remember that 120 volts is the RMS value not the peak, which is over 300 volts.