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Battery life: 2xRC Motor vs. 1xPF Motor


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#1 andythenorth

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Posted 11 August 2010 - 08:41 PM

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The PF motor has more torque than the RC motor, but it can't get the power to the ground due to wheelslip.

More driven wheels should mean less slip.

So I wondered, if the RC motor is lower torque, does it also draw less power?  And then how might battery life fare with 2x RC motors (not close to stall) compared to 1 PF motor which alternates between wheelslip and near-stall?

I did study physics in school, but electronics never stuck in my brain  :blush:
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#2 peterab

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Posted 12 August 2010 - 02:53 AM

View Postandythenorth, on 11 August 2010 - 08:41 PM, said:

Posted Image

The PF motor has more torque than the RC motor, but it can't get the power to the ground due to wheelslip.

More driven wheels should mean less slip.

So I wondered, if the RC motor is lower torque, does it also draw less power?  And then how might battery life fare with 2x RC motors (not close to stall) compared to 1 PF motor which alternates between wheelslip and near-stall?

I did study physics in school, but electronics never stuck in my brain  :blush:

I've modified my green cargo train to have two RC motors and I'm very pleased with it. I'll be testing its pulling power at a show 0n the 22nd. I think it works well because the weight of the batteries is centrally mounted between the motors, and the loco is heavier than the new yellow cargo train.

To correct the wheelslip you may want to add more weight above the PF motor. Or perhaps try replacing the traction bands on the wheels with larger O-rings.

You will probably find the RC motors get caught under the new train baseplates since they require a 9V style plug which sticks up a bit. A second PF motor with the above changes might be better.

#3 hoeij

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Posted 12 August 2010 - 03:01 PM

View Postandythenorth, on 11 August 2010 - 08:41 PM, said:

Posted Image

The PF motor has more torque than the RC motor, but it can't get the power to the ground due to wheelslip.

More driven wheels should mean less slip.

So I wondered, if the RC motor is lower torque, does it also draw less power?

The new train motor was advertised as using less electricity than the RC motor.

#4 Richie

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Posted 12 August 2010 - 03:41 PM

andythenorth, do you mean the PF train motor?
If so, what I've heard of, is that the PF train motor, using the battery box find in the two regular train sets, uses six AAA-size batteries. The RC train motor uses six AA-size ones, but it seems the PF motor is still more powerful.

You can try to look here. The total performance of every motor is tested, very useful. To me anyway.  :classic:

It's multifunctionomical.

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#5 hoeij

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Posted 12 August 2010 - 04:50 PM

View PostRichie, on 12 August 2010 - 03:41 PM, said:

andythenorth, do you mean the PF train motor?
If so, what I've heard of, is that the PF train motor, using the battery box find in the two regular train sets, uses six AAA-size batteries. The RC train motor uses six AA-size ones, but it seems the PF motor is still more powerful.

You can try to look here. The total performance of every motor is tested, very useful. To me anyway.  :classic:

You can see in the tables that under a high load (0.85 N.cm) the motor is pulling about 0.37 amps.
Note that with this much torque, the wheels will definitely be slipping unless you replace the
rubber bands by different ones with more traction.

Although the AA batteries can crank out more amps than the AAA batteries,  the AAA batteries can
crank out more than 1 amp, i.e. more than 3 times what the motor will actually use when it is under
a high load.  The AA vs AAA batteries makes no difference in pulling power (it only affects how
many hours the train can run).


Considering that the new motor is so much stronger than the previous one, you could pull a nice
long train if you replace the rubber bands by new ones with more traction.

If you can improve traction, then one PF train motor will pull as much as two RC train motors,
and do so while using much less current.

Edited by hoeij, 12 August 2010 - 04:53 PM.


#6 Goldenmasamune

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Posted 12 August 2010 - 07:33 PM

Lego has released new wheels (again) that have even better traction. With these new wheels the PF motor doesn't slip at all. at least hasn't slipped for me yet, except a little when starting it up.

the RC wheels were so bad, the RC cargo train couldn't even pull the cars that came with it.

#7 andythenorth

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Posted 12 August 2010 - 07:40 PM

View PostGoldenmasamune, on 12 August 2010 - 07:33 PM, said:

Lego has released new wheels (again) that have even better traction. With these new wheels the PF motor doesn't slip at all
Interesting.  Are these on lego.com anywhere?
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#8 Goldenmasamune

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Posted 12 August 2010 - 08:14 PM

View Postandythenorth, on 12 August 2010 - 07:40 PM, said:

Interesting.  Are these on lego.com anywhere?

No, I just got them with my new cargo train. It came with 8, so i tossed the dummies onto the PF motor I put on my modified 7898. I'd say they have more than double the traction of the wheels with the gray bands.

#9 Richie

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Posted 12 August 2010 - 08:22 PM

You can order them at Pick a Brick.

In this Railbricks blog, Anthony Sava writes about an even better solution, resulting in more traction, although it's not a 100% LEGO solution.

It's multifunctionomical.

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#10 andythenorth

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Posted 12 August 2010 - 09:34 PM

View PostGoldenmasamune, on 12 August 2010 - 08:14 PM, said:

No, I just got them with my new cargo train. It came with 8, so i tossed the dummies onto the PF motor I put on my modified 7898. I'd say they have more than double the traction of the wheels with the gray bands.
Ah ok.  I think I have these wheels already  :classic:
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#11 hoeij

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Posted 12 August 2010 - 10:05 PM

View PostGoldenmasamune, on 12 August 2010 - 08:14 PM, said:

No, I just got them with my new cargo train. It came with 8, so i tossed the dummies onto the PF motor I put on my modified 7898. I'd say they have more than double the traction of the wheels with the gray bands.

My 7938 has the same gray bands as the previous passenger train 7897.

What color are the bands on your new wheels?

#12 Goldenmasamune

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Posted 12 August 2010 - 10:13 PM

View Posthoeij, on 12 August 2010 - 10:05 PM, said:

My 7938 has the same gray bands as the previous passenger train 7897.

What color are the bands on your new wheels?


The new bands are clear. They seem to have more than double the traction of the grey bands.

The three color bands i've seen are:

Black: Almost no traction
Gray: Good traction
Clear: Amazing traction

#13 hoeij

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Posted 12 August 2010 - 11:52 PM

View PostGoldenmasamune, on 12 August 2010 - 10:13 PM, said:

The new bands are clear. They seem to have more than double the traction of the grey bands.

The three color bands i've seen are:

Black: Almost no traction
Gray: Good traction
Clear: Amazing traction

That's excellent news.  With the new bands it should then be easy to pull two 7938's with one motor,
without struggling to make it through curves as one can see in this video:  (not mine)

  

#14 Goldenmasamune

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Posted 13 August 2010 - 04:57 AM

View Posthoeij, on 12 August 2010 - 11:52 PM, said:

That's excellent news.  With the new bands it should then be easy to pull two 7938's with one motor,
without struggling to make it through curves as one can see in this video:  (not mine)

  


I think you'll be happy. So far I've been able to pull 15+ cars through curves and switches with absolutely no problems.

In fact, i just made a quick oval track on my table (16 curve tracks, 14 straight) and tossed 16 cars behind the new cargo train. They were as follows:

3 custom tanker cars (the andythenorth ones)
3 cars from 2010 cargo train (tanker, flatbed with cars, flatbed with big box)
4 cars from RC cargo train (flatbed with car, small red thing, crane car, modified box car)
1 long car from freight and crane railway
1 My own train hopper car
1 my own train log car
1 emerald night passenger car
1 box car from 4512
1 flatbed car with cargo from 4512

I would have added more, but at this point there was only a small space between the front of the engine and the rear of the car in the back. It was a little slow getting started, but held up fine. Barely any wheel slipping at the start. I could imagine if I were on a longer layout, and not going through 16 curve track at the same time, the motor could easily handle 10 more cars (as long as they weren't huge heavy passenger cars)

Edited by Goldenmasamune, 13 August 2010 - 06:08 AM.


#15 Brickviller

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Posted 13 August 2010 - 08:21 AM

I tried also a thing with the new PF cargo train, it doesn't slip at all and could still pull over 6 cars (okay not that much but still) and the old passenger train couldn't even get them moving :wacko:

#16 legoboy3998

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Posted 14 August 2010 - 03:42 AM

Thats interesting about the clear bands on the new train wheels.  I bought the new Cargo train set back during brick-world and it came with the gray bands as best as I can tell.  They must have replaced the bands after the first production run.  Hopefully they will put the PF train motor up on S@H soon.

Sal
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