Real power of Lego motors?

[ben20]

What/who is correct about torque and current (consumption)?

http://powerfunction...fault.aspx#8882

http://www.philohome...ec/pfcurves.htm

http://www.philohome...s/motorcomp.htm ( go to Stalled characteristics)

https://books.google...f=false�������� (GO TO PART 3 MOTORS)

Edited February 5, 2015 by ben20

[Omikron]

The answer to your question is : The one you trust.

[Tommy Styrvoky]

They can varry because of different production batches and differences in power source.

Edited February 5, 2015 by Tommy Styrvoky

[ben20]

They can carry because of different production batches and differences in power source.

A difference of 1-5Ncm ok, but 75Ncm between the same xl motor? (between Sariels book and Lego site)

[aol000xw]

I have seen old motors crawling and loosing most of it's torque, I guess because the magnets lost strength overtime, but those were using not neodymium magnets, and I don't know if that applies here.

[sama]

I have a question, is it better to use 6, 1.2v rechargeable batteries, or use 6, 1.5v alkaline batteries? All I can read is that 7.2v performance is lower than the performance with 9v (for Power Function elements, like in 8043). But a while back, people told me it is better to use the rechargeable batteries.

Edited February 5, 2015 by sama

[Sariel]

The values in my book are taken directly from Philo. If they are different than declared at his website, then he probably updated his website since then.

As for difference between Lego data and Philo's data: well, we know how Philo got his numbers because he's shown us the entire process. Lego showed nothing. So I guess anybody can repeat Philo's tests and check if he gets the same values.

I have a question, is it better to use 6, 1.2v rechargeable batteries, or use 6, 1.5v alkaline batteries?

Interesting question, I have recently observed that RC buggy motors powered from the RC unit perform much better with 1.2V Eneloop rechargeable batteries than with brand new 1.5V Duracell ones. I mean, it was a very, very clear difference and these Eneloops weren't even freshly loaded.

Edited February 5, 2015 by Sariel

[Milan]

I have a question, is it better to use 6, 1.2v rechargeable batteries, or use 6, 1.5v alkaline batteries? All I can read is that 7.2v performance is lower than the performance with 9v (for Power Function elements, like in 8043). But a while back, people told me it is better to use the rechargeable batteries.

People here who knows a thing or two about that often recommend use of the rechargeable batteries. Even though 7.2V (or 7.4V for battery box) is lower than 9V, in reality rechargeable ones are better. When under stress, they provide more constant flow, while 9V ones can "sag" and their voltage can drop bellow 7.2V. Also, 7.2 provide good flow even when they near the end of the capacity, while 9 drop flow as they deplete.

Edited February 5, 2015 by Milan

[Saberwing40k]

Now hold up here, I discovered something interesting. Lego uses a really weird measure for the torque of the XL motor, something I have never seen before: mNm. I presume this stands for milli-Newton-meter, which would actually be Newton-Millimeter. Therefore, going by what they say, XL motors produce 90.4 Newton-Millimeters, or 9.04 Ncm/Newton-Centimeters of torque. That is actually far more in line with what Philo measured, but not for stalled torque. He himself noted that the stalled torque measurement was very imprecise. So, where does that leave us? That leaves us with Philo stating that the Power Functions XL motor produces 14.5 Ncm of torque, and drawing 550 milliamps, and Lego stating that the XL motor produces 9.04 Ncm of torque, and drawing 600 milliamps of current. I can think of a few possibilities to explain this discrepancy, which are as follows:

• Lego is being conservative with their estimates.
  
• Philo's test was not as accurate as Lego's
  
• Lego used a bad sample
  
• Philo used an unusually good sample.
  
• This may sound crazy, but might Lego have lowered the torque of the XL motors? In order to test this, one would have to find an old sample, from an MISB 8275, or 8258, and compare that motor with a new one, from 42030.
  

I must say, you would think that Lego, a massive corporation, would have access to some kind of industrial torque sensor to test their motors, but I dunno.

Edited February 6, 2015 by Saberwing40k

[torso]

Lego is probably stating the specification of the current. This specification should cover the worst case scenario and is always higher than measured values. This number is important when choosing power supply, but isn't a good indicator of performance.

Stalled torque is usually a lot higher than the torque you get under normal operation. Doesn't tell you much about performance. The high number is good for marketing purposes though.

My guess is that the torque that Lego specifies is the only useful number for performance. It's probably measured when the motor is working under ideal circumstances. Hopefully an average of several motors.