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Power the brain with a 3S LiPo
05-02-2018, 07:57 PM
Post: #1
Power the brain with a 3S LiPo
Hi!

I have searched the site, but do not find any information about max supported voltage..

The robot kit use 6x1.5V = 9V

Can I connect a 3S LiPo without frying the brain?

I have the V3.1 shield - there is two Vin (one in a corner and one in the center)

Where do i connect the LiPo?
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05-03-2018, 12:10 AM (This post was last modified: 05-03-2018 04:20 AM by Vaygr.)
Post: #2
RE: Power the brain with a 3S LiPo
I'm personally using rechargeable Ni-MH AA batteries, so it's 6 x 1.2 V = 7.2 V. And the robot works fine. The official design was probably limited to only 6 AA batteries due to space restrictions so as to keep the overall design more compact.

From the Arduino Leonardo tech specs: https://store.arduino.cc/arduino-leonardo-with-headers
Input Voltage (Recommended) 7-12V
Input Voltage (limits) 6-20V

So, you could safely use a 3S LiPo rated 11.1 V. However, i'm not sure about the optimal mAh and C rating. Huh
You can connect the LiPo battery via a 2.1 mm DC power connector to the power jack in the Leonardo.

I'm trying to calculate the optimal battery specifications based on the motors...
The datasheet for the stepper motors sold by JJRobots with model number: MT-1703HS168A
http://www.motechmotor.com/products_deta...=70&page=1

The rated current of the motor is 1.68 A/phase according to its datasheet.
Since the motor is in a bipolar configuration, for both phases, each motor should draw 2 x 1.68 A = 3.36 A.
So, the total current drawn by two bipolar stepper motors = 2 x 3.36 A = 6.72 A

Max Current Draw = Capacity x C-Rating
If the C-Rating of the LiPo battery is 30 C, then its minimum capacity = 6.72 / 30 = 0.224 Ah = 224 mAh.

But, i'm a bit confused if using for example a 2200 mAh LiPo at 30 C, then the current output from the battery would be 66 A - won't it cause overheating or permanently damage the motors?
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05-03-2018, 06:42 AM
Post: #3
RE: Power the brain with a 3S LiPo
(05-03-2018 12:10 AM)Vaygr Wrote:  I'm personally using rechargeable Ni-MH AA batteries, so it's 6 x 1.2 V = 7.2 V. And the robot works fine. The official design was probably limited to only 6 AA batteries due to space restrictions so as to keep the overall design more compact.

From the Arduino Leonardo tech specs: https://store.arduino.cc/arduino-leonardo-with-headers
Input Voltage (Recommended) 7-12V
Input Voltage (limits) 6-20V

So, you could safely use a 3S LiPo rated 11.1 V. However, i'm not sure about the optimal mAh and C rating. Huh
You can connect the LiPo battery via a 2.1 mm DC power connector to the power jack in the Leonardo.

I'm trying to calculate the optimal battery specifications based on the motors...
The datasheet for the stepper motors sold by JJRobots with model number: MT-1703HS168A
http://www.motechmotor.com/products_deta...=70&page=1

The rated current of the motor is 1.68 A/phase according to its datasheet.
Since the motor is in a bipolar configuration, for both phases, each motor should draw 2 x 1.68 A = 3.36 A.
So, the total current drawn by two bipolar stepper motors = 2 x 3.36 A = 6.72 A

Max Current Draw = Capacity x C-Rating
If the C-Rating of the LiPo battery is 30 C, then its minimum capacity = 6.72 / 30 = 0.224 Ah = 224 mAh.

But, i'm a bit confused if using for example a 2200 mAh LiPo at 30 C, then the current output from the battery would be 66 A - won't it cause overheating or permanently damage the motors?

The stepper drivers handle Voltage/Current use for the motors.

So all is powered from the Arduino Leonardo?
I did believe there was more powerful regulators on the brain shield and that I should use one of the vin on the brain when connecting a LiPo?
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05-03-2018, 09:40 AM
Post: #4
RE: Power the brain with a 3S LiPo
Almost any Lipo battery can deliver enough current by default. The B-robot would need peaks of 1 Ampere to move the motors, not too much for many batteries (Alkaline or Ni-Mh included)
And yes... we opted for 6xAA batteries to keep the battery holder contained inside the frame and the center of gravity low at the same time :-)
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