Electric motors would not work on the moon

[Rob260259]

Now hear this:

"On a hot day on earth electric motors can fail. The max surrounding temp for electric motors is from 40c to 70 c tops the , moon is 126c In the near vacuum on the moon the heat could not escape there is no air temp .only the radiated heat from being exposed to the sun, So the mptor would heat to 126 without being on. turn it on it gets hotter again and it cant be air cooled!"

and

"The basic ambient temperature rating point of nearly all electric motors is 40° C. This means that a motor, rated for 40° C ambient, is suitable for installation in applications where the normal surrounding air temperature does not exceed 40° C. This is approximately 104° F. A very warm room. This is the starting point. FROM Motor and drives dot com "

and

"When the motor is operated at full load, it has a certain amount of temperature rise. The amount of temperature rise is always additive to the ambient temperature. For example, U frame motors were designed for Class A insulation and a maximum temperature rise by resistance of 55° C. When operated in a 40ˆ C ambient temperature, this would give a total average winding temperature of 40° (ambient) + 55° (rise) or 95° C."


I'm not an engineer and unwitting about this. Where to find a few pages for a solid debunk?

[Allan F]

First of all, the word "ambient" does not relate to the moon (edit: Unless you are buried in the ground). Vacuum has no ambient temperature. The 126 C refers to temperature in the soil at high lunar noon, and does not relate to Apollo (if that's the subject) since they all landed at lunar dawn, and took off again in the mid-morning (relative).

Then there's the whole problem with the people who built the stuff knew about this, and could provide other means of cooling (radiative and conductive).

Also, electric motors can be designed with higher heat tolerances in mind, so even if heat becomes a problem, it will take a while before it does.

[cjameshuff]

I'm not an engineer and unwitting about this. Where to find a few pages for a solid debunk?

Where to start? It's all nonsense.

Those temperature limits are a plain fabrication. You can easily find motors that can operate above 70 C. The limiting factors are largely the permanent magnets for the motors that use them, and insulation and melting point of the materials for the motors that don't. Here's a motor that can operate at 540 C (enough to glow visibly in the dark): http://www.techbriefs.com/component/content/article/2241

The rover wouldn't immediately heat to 126 C. The landings were at local morning, and the surface was still cool. From http://www.hq.nasa.gov/alsj/a17/A17_LunarRover2.pdf, the highest temperature components on the rover were apparently rated for 85 C.

[cjameshuff]

"When the motor is operated at full load, it has a certain amount of temperature rise. The amount of temperature rise is always additive to the ambient temperature. For example, U frame motors were designed for Class A insulation and a maximum temperature rise by resistance of 55° C. When operated in a 40ˆ C ambient temperature, this would give a total average winding temperature of 40° (ambient) + 55° (rise) or 95° C."

Class A is the insulation class with the lowest temperature rating, with a maximum operating temperature of 105 C. Now why would he pick that one?

Class H is the highest in that classification system, with an operating temperature of 180 C. With his own number of 119 C for surface temperature, that would give a 54 C margin. (Which is much higher than the actual surface temperature of around 50-70 C, which actually fit within the narrow temperature range he gives for "max surrounding temp": http://www.workingonthemoon.com/WOTM-ThermalEnvrnmnt.html)

And of course, the equilibrium temperature of the rover's motors would be something completely different. The rover isn't a pile of regolith, it's a vehicle designed and built by people thinking about temperature control.

For more reading: http://www.hq.nasa.gov/alsj/lrv_thermal_alsj.pdf

It looks like the highest motor temperature recorded was on Apollo 17, at 270 F (132 C).

[Luckmeister]

Class A is the insulation class with the lowest temperature rating, with a maximum operating temperature of 105 C. Now why would he pick that one?

Because he likes the taste of cherries?

[JayUtah]

http://www.motorsanddrives.com/cowern/motorterms4.html

[JayUtah]

The motors on the LRV were pressurized with nitrogen precisely for heat transfer.  Once transferred to the motor case, heat can be conducted to the vehicle chassis, radiated away, etc.

[DataCable]

This one could go in the old HB Contradictions thread:  According to MrGuitarDeath several years ago on IMDB, electric motors on the moon would go six times as fast as on the earth, because the only factor limiting a DC motor's rotation rate is gravity-induced friction.

[Noldi400]

Odd in a way that he would pick on the motors.  There were numerous electronic components that were more heat sensitive.

Allan F made a point that Brit Danny Baker expressed as: "And because, of course, it was designed by human brains and geniuses and not a lot of people sitting and tapping away at the internet who don't gotta get up and go to work in the morning. Who do you trust here?"

[ka9q]

This one could go in the old HB Contradictions thread:  According to MrGuitarDeath several years ago on IMDB, electric motors on the moon would go six times as fast as on the earth, because the only factor limiting a DC motor's rotation rate is gravity-induced friction.

So motors on spacecraft in zero gravity can go infinitely fast?

[raven]

I wonder what the Rob's conspiracy theorist would think of the Lunokhod rovers? Assuming they ever heard of them in the first place.

[qt]

This one could go in the old HB Contradictions thread:  According to MrGuitarDeath several years ago on IMDB, electric motors on the moon would go six times as fast as on the earth, because the only factor limiting a DC motor's rotation rate is gravity-induced friction.

So motors on spacecraft in zero gravity can go infinitely fast?

That's why you're not allowed to use computers or CD players during the beginning and ending of aeroplane flights.  If people noticed the drive motors slowing down during the ascent and speeding up during the descent, it would unmask the hoax conspiracy.

[Rob260259]

I wonder what the Rob's conspiracy theorist would think of the Lunokhod rovers? Assuming they ever heard of them in the first place.

That's a good one. I'll ask him about the Luna 17 & Luna 21 missions and the Lunokhod rovers they carried.

[Rob260259]

http://www.motorsanddrives.com/cowern/motorterms4.html

Exactly what I was looking for.
Thanks a lot!

[DataCable]

So motors on spacecraft in zero gravity can go infinitely fast?

I seem to recall posing some variant of this very question (after picking myself up off the floor from a laughter-induced coma) and he responded that a motor in zero-g would continue to speed up until it burns out.  I tried looking up the thread, but it's apparently been deleted, as the only references I could find were dead links to it in the cosmoquest archive.