Practical Motors - beginner question

Discussion in 'Homework Help' started by M11, Dec 27, 2010.

1. M11 Thread Starter New Member

Dec 27, 2010
18
1
Hi,

I am working on a project where I have to use a DC motor. I have never used a motor before. How can I make sure that the maximum current does not exceed a certain value ?
I have not chosen the value of the voltage supply yet.

also, if someone can explain the parameters in the motor plate in details I would really appreciate it. I have searched about it, but all the websites I found explain how to do the theoretical calculations only.

Thanks,

Last edited: Dec 27, 2010
2. mik3 Senior Member

Feb 4, 2008
4,846
63
You can use PWM and a current sensor to limit the current.

3. thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
The current a motor draws is related to the amount of loading the shaft has (torque requirements).

What current did you want to limit? Typically, the driver circuit is designed to be capable of the anticipated power levels that the motor will need.

More insight as to the project may help with recommendations on the motor and the driving circuitry.

4. ashish19183 New Member

Sep 16, 2009
13
0
which kind of motor do you wanna use?? can you tell me the specs

you want to run in one direction or bi-directional ?????

in DC motors u can use resister shunt to monitor current of motor

and you can vary motor speed by PWM control .... if yo give motor details i can

help u in better way

5. M11 Thread Starter New Member

Dec 27, 2010
18
1
Thank you guys for your response.

The project is to build an RC plane. The current through the motor circuit must not exceed 20A. There are no constraints on other parameters. I had a look at nearby hobby store, and I found a motor that can deliver a reasonable speed. The specs of the motor are given below. I can afford to buy online, so if you have any suggestions for any motor please inform me.
Thanks,
motor:
Technical Specifications for Hacker A20-22L

• Motor Type: Brushless, Outrunner
• Weight: 57g (2.01 oz)
• Power: 200 Watts
• RPM/Volt (KV): 924
• Continuous Current: 6-14A
• Burst Current: 17A
• Recommended Propeller: APC 10x4.7
• Recommended Lithium Polymer Battery: TP-1350-3SPL2 or TP-2100-3SPL2

6. thatoneguy AAC Fanatic!

Feb 19, 2009
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718
The aircraft the size that that one (10x4 prop!) appears to be moving are nowhere near cheap (I fly RC too, money sink!).

That motor won't draw more than 17A peak, so you are fine. It may rarely peak higher than rated at takeoff for short periods of time. BLDC are 3 phase motors, and the controller is a DC to 3 phase AC inverter. The frequency of the output AC is what determines the speed of the motor. Some ESC-BLDC controllers have an trimmer adjustment for max current draw/speed, or used to.

I'd be wary of adding anything other than factory modules rated for RC aircraft in an RC Airplane where connection to the radio is in the loop. It's a lot of money zipping around at 80mph 100+feet off the ground, so nearly any failure is "catastrophic" when it hits the ground.

7. Audioguru New Member

Dec 20, 2007
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My ultra-micro P51 Mustang RC airplane has been wacked by the ground many times. The ground is soft and covered with grass so the airplane bounces and one time kept on flying.

My ultra-micro RC Piper Cub hit an observer one time (and has hit my belly many times). He laughed. It weighs less than one ounce and flies slowly.

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9. thatoneguy AAC Fanatic!

Feb 19, 2009
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His setup is a tad different though, the propeller alone is longer than the indoor airplanes. Those little ones are a TON of fun though, the "pager motor" powered airplanes and similar helos.

10. Audioguru New Member

Dec 20, 2007
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The prop on my ultra-micro RC P-51 Musang is 5". His big heavy airplane has a 10" prop.
The wingspan is 16" and the weight with 4 gram battery is only 35 grams. The motor is strong enough to pull the airplane straight up. It flies level at up to 30mph. Each flight lasts 10 minutes to 15 minutes depending on how many manouvers.

My ultra-micro airplanes have never flown indoors. But always at parks when the wind is 15mph or less.