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Old 02-01-2014, 12:19 PM   #51
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Originally Posted by Bob.Kerns View Post
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The sane way to do it would be with a big power resister, and just worry about efficiently dumping the heat into the environment (and not the electronics or the user)...
But wouldn't this mean that anyone going down a big hill on a segway would be adding to Global Warming?
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Old 02-01-2014, 06:18 PM   #52
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Sorta what I said earlier....................

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And a bright light is just a heater. A 100-watt bulb dissipates 100 watts. Yes, a heater could certainly be added, for those cases where the battery is already "full".

My back-of-the-envelope calculation says that a 250-watt lightbulb (specially made for 75-volt service) would do the trick for the limited case.
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Old 02-10-2014, 07:21 AM   #53
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Originally Posted by dale@thecoys.net View Post
Sorta what I said earlier....................

My back-of-the-envelope calculation says that a 250-watt lightbulb (specially made for 75-volt service) would do the trick for the limited case.
Yes, but a 250-watt lightbulb will far exceed federal maximum standards for automobiles. Why would we want one on a Segway?

The only solution is to make it a very inefficient lightbub (in the visible spectrum).

In other words, a space heater. And since nobody deliberately designs inefficient light bulbs, you may as well go with a power resistor and a separate LED lighting system. The result will be more reliable, and cheaper than some design based on specialized bulbs.

Add to this the fact that the power to be dissipated depends on the slope and instantaneous demands, and I just don't see lightbulbs as being a suitable solution to dumping the energy. It could be done, but the illumination aspect is not working to your advantage.

Also, I'm taking your 250 W at face value. I presume your calculations were reasonable based on the physics of the mass of rider + segway descending at some particular rate.

That's a reasonable approach for estimating average power, but we have to consider that the motors are capable of much higher peaks -- almost 2 KW apiece. (per Doug Field, in a post here: http://forums.segwaychat.org/archive...hp/t-9400.html)

As I stated, an incandescent bulb is a space heater operating near the failure point. They're not very tolerant of being overdriven for even short periods of time. They have very low thermal mass, so they heat up very quickly.

As an exercise in physics, it makes perfect sense. As a practical design -- not so much. A lot of engineering consists of considering "what could possibly go wrong with this perfectly logical plan?"
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Obviously, we can't have infinite voltage, or the universe would tear itself to shreds, and we wouldn't be discussing Segways.
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Old 02-10-2014, 12:01 PM   #54
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Thanks, Bob.

I am quite aware that a light bulb would not be a good solution (for all of the reasons you mentioned, plus a few more). I stated it that way so that most folks would have some way to compare it with a familiar object.

Saying "power resistor" or "small space heater" or "coffee pot" or "crock pot" would have worked, of course - I'm just not sure it would have been quite so illuminating.

Are you still intending to write up the physics, to help Karl?
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Old 02-11-2014, 10:08 AM   #55
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Quote:
Originally Posted by dale@thecoys.net View Post
Thanks, Bob.

I am quite aware that a light bulb would not be a good solution (for all of the reasons you mentioned, plus a few more). I stated it that way so that most folks would have some way to compare it with a familiar object.

Saying "power resistor" or "small space heater" or "coffee pot" or "crock pot" would have worked, of course - I'm just not sure it would have been quite so illuminating.

Are you still intending to write up the physics, to help Karl?
It is, indeed, a good way to illuminate the topic!

It also illustrates nicely the difference between physics and engineering. All engineering is built atop of physics, but engineers search for solutions among a myriad of physical constraints.

I am still intending to write something up, but the earliest it could happen is this weekend. Being sick for a month has left me a bit behind.
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Obviously, we can't have infinite voltage, or the universe would tear itself to shreds, and we wouldn't be discussing Segways.
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Old 04-13-2014, 12:19 PM   #56
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.... All engineering is built atop of physics, but engineers search for solutions among a myriad of physical constraints.

I am still intending to write something up, but the earliest it could happen is .......
I believe this writeup would be helpful, if you find the time to do it.
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Old 04-13-2014, 10:51 PM   #57
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I believe this writeup would be helpful, if you find the time to do it.
I haven't forgotten about it, but got a software release to get out shortly, so it's not going to me Real Soon yet...
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Obviously, we can't have infinite voltage, or the universe would tear itself to shreds, and we wouldn't be discussing Segways.
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