Brushed/Brushless motors, speed controls, gear drives Discuss all aspects of brushless motors, brushed motors, speed controls (ESC's), gear drives and propellers in this forum.

Question about Motors

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Old 09-12-2006, 07:44 PM
  #26  
jdetray
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Default RE: Question about Motors

The ESC has nothing to do with the problem, except that it is cutting power to the motor -- as it is designed to do -- when the battery voltage drops too low.

The issue here is that your power system draws more current than the battery can supply. When that happens, the battery voltage drops, the ESC senses the voltage drop, and it cuts power to the motor.

I can think of two possible reasons why the battery voltage is dropping:
1. The C rating of the battery is too low. Together, the C rating and the capacity (mAh) determine the maximum current the battery can provide. 20A may simply be too much for this particular battery. You can either reduce the current (smaller prop) or get a more robust battery (one that can handle 20A).
2. The battery is defective, damaged, or at the end of its life.

- Jeff
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Old 09-12-2006, 08:48 PM
  #27  
Cyrus Abdollahi
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Default RE: Question about Motors

Crap.........the battery is NEW and can do up to 33A continous!

The 3s can do up to 40A!

This is not adding up.........grrr
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Old 09-13-2006, 09:16 PM
  #28  
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Default RE: Question about Motors

Problem solved, I put a 4s and burned it out, smoke went everywhere!! LOL STUPID STUPID STUPID!
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Old 09-15-2006, 05:41 PM
  #29  
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Default RE: Question about Motors

Ok....I got a Castle Creations Pheonix 45 ESC and wired it up to my AXI 2814/10....this stupid thing STILL cuts off becuase the battery voltage drops too low. I tried using a 3s and a 2s (both 2100mAh). I set the cuttoff voltages to 9 and 6 volts, respectively. (3v/cell as recomended per thunderpower).

I used all kinds of props and they ALL cut off!

10x4.7
9x6
8x6
7x5

ALL keep cutting off after half throttle becuase the battery goes down to low.

BUT AXI say this motor is for a 2s or 3s!!!!

I have my JR set to +/- 100%......WHATS GOING ON!??????
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Old 09-15-2006, 07:41 PM
  #30  
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Default RE: Question about Motors

Hi Cyrus-

A couple of questions.

1. Are you starting with fully-charged batteries when testing your power system?

2. What is the voltage of your battery packs, fresh off the charger?

3. How much current is being drawn before the motor cuts off?

4. Exactly which batteries are you using?

- Jeff
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Old 09-15-2006, 08:09 PM
  #31  
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Default RE: Question about Motors

Yes, the batteries were fully charged.

I think something like 8.46 volts fully charged on the 2s. I know the batteries are not bad, they have never been used before. The 3s is my friends, and he flies his e-heli with it all the time, its not bad either.

The damn thing only peaked at 25A, and this is a 45A speed controller.

The battery is Thunder Power 2100mAH/7.4V

and APex 2100mAH 11.V 15C

What is going on?
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Old 09-15-2006, 08:14 PM
  #32  
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Default RE: Question about Motors

Here are the graphs of the motor running:








hope this helps, because im damn confused at this point......................sigh.

Edit: I got bold on this run and set the cut off voltage to 5V, and it STILL cut off on me!? That battery did not even go below 5V, and the current did not go above 45A!?!?!?

Edit 2: Accidentally had two graphs of amps, changed one to power***

Edit 3: That run was with an 8x6 prop.
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Old 09-15-2006, 08:32 PM
  #33  
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Default RE: Question about Motors

Well, Bingo on the 2s! You got it jdetray!

This 2s is a 10-12C, aka its upper limit is 25A. It can burst for 33A. Plain and simple, this battery is TOO SMALL for this motor. This axi can go all the way up to 40A. Now way this battery will work.....DAMN, that means more money I have to spend now.....crap.

As for the 3s, it's a 15C, that means 31.5A....so that one should be somewhat better.....(NOTE, those graphs are with a 2s, NOT 3s).

Hmmmmmmmm.......................at least that explains one thing. The battery is not bad, it's just WRONG. [:@]

The battery was under harsh loading conditions, and as a result we can see the voltage drop significantly.
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Old 09-15-2006, 08:38 PM
  #34  
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Default RE: Question about Motors

I think I need this battery pack.

4000 mAh, 7.4V (charge as 2 cells), 13G wire, 4-pin balancer connector
Rating: 12C (48A) continuous, 20C (80A) burst
Dimension: 50mm x 128mm x 17mm

Weight: 120gm
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Old 09-17-2006, 09:31 PM
  #35  
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Default RE: Question about Motors

Ahh success! I bought an e-flite 480 brushless motor. It runs all the way up to full throttle on that lipo. I think the axi motor I was using was way too big for that airplane anyways!

I ran it on my bench at full throttle for 6:40! That's a long time for continous full throttle!
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Old 09-17-2006, 11:49 PM
  #36  
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Default RE: Question about Motors

Hi Cyrus-

I'm glad you've finally got a power system that appears to work.

I strongly suggest that you do not perform extended full-throttle bench testing of your motors. It's a very good way of overheating the motor or ESC, for two reasons.

First is that most power systems draw more current during static testing than they do in flight. Second is that you don't have the benefit of cooling airflow due to the plane moving through the air.

If the magnets in the motor overheat, they permanently lose some of their strength.

It's OK to make brief full-throttle runs on the bench, just long enough to check current and voltage.

- Jeff
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Old 09-18-2006, 12:21 AM
  #37  
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Default RE: Question about Motors

No worries, I have temperature probes that monitor the temperature. Everything was just warm to the touch after a 7 min run!

It is prefectly safe to run a full duration run, provided you have the proper monitoring equipment.

I've looked up all the data, and they should run below 50C. The temperature probes never went above 40! And this was without any prop airflow over the battery or ESC. The prop was on backwards so that it would create downforce and not lift off the table. Now I have to get my thrust stand hooked up so I can measure the thrust and RPM during a bench test.

**The Fun begins**
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Old 09-18-2006, 12:37 AM
  #38  
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Default RE: Question about Motors

Putting the prop on backwards does not change the direction of the airflow, though it does reduce the airflow.

To change the direction of the airflow, you must run the motor in the opposite direction.

- Jeff
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Old 09-18-2006, 12:49 AM
  #39  
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Default RE: Question about Motors

Yes, I should have said I switched the leads.
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Old 09-18-2006, 06:45 PM
  #40  
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Default RE: Question about Motors

wow, I just got a 19 min run on a 7x5 prop!! Full throttle continouos!
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