Neat power cabling for arduino, raspberry pi and two H-bridge motor

[thiezn]

Hi Guys,

Spoiler alerts ** I'm a real beginner on working on electronics so please forgive me for asking the obvious **

I'm attempting to build myself a 4WD robot using an Arduino Mega to control the motors and sensors, a Raspberry Pi powering a Pi camera and two Dual H-Bridge to control the direction of my four DC motors. The Arduino will power various sensors like a IMU and HR-SR04 distance sensor. I’ve purchased a Arduino Mega sensor shield to be able to easily expand the board with additional sensors.

The raspberry and Arduino will be talking to each other through the serial bus sending and receiving data for processing. Anyway I think I've got all the parts sorted but still am struggling a bit with how to power them all using rechargeable batteries. I’ve tried to think about what kind of sensors I’d like to use and add up the required Amps.

Here’s the list I’ve got at the moment:

• Count Module Total Current (mA)
• 1 Raspberry Pi 2 B 1200
• 1 Pi Camera 250
• 1 Pi HDMI 50
• 1 Arduino Mega (max) 200
• 1 HR-SR04 distance sensor 15
• 1 GPS module 70
• 3 Servo motor 120
• 1 IMU 6 Degrees 40
• 1 Microphone 48
• 1 Speakers Not sure on model yet can require a lot mA’s 400 (estimation)
• 4 DC Motors 400

Total current required (mA) 2618

To power it all I thought to purchase a Lipo 186500 battery holder with two 3.7V / 3000mA rechargeable batteries to give a total of 7.4v. The raspberry Pi is apparently very sensitive to voltage drops so I’ve purchased the following UBEC to go with it.

Raspberry Pi UBEC

Now for my question, I need to get power and ground cables from my battery holder to the raspberry UBEC, the arduino (perhaps using the 2.1mm connector) and to the two Dual H-Bridge circuits. I’ve tried to find a proper way to connect these cables together but the best I came up with is to twist several separate cables together and wrap them in electric tape. This doesn’t really feel like a proper solution though but couldn't find anything online to make this kind of power cable splitter connections in a proper way.

Would someone be able to point me in the right direction. Also, if someone sees a flaw with my power calculations I’m very open to suggestions!

Cheers,
Thiezn

[MarkT]

Use a separate power source for the Pi/Arduino/sensors from the supply to the motor
drivers. Don't try and run from a regulator off the main battery because that voltage will dip
and crash your Arduino and Pi. You want the logic to have a supply that will last longer
than the motor battery anyway, otherwise the first symptom of low battery is the thing
goes haywire, Pi crashes, SDcard corrupted... You want the first symptom to be that the motors
get sluggish and you have time to shutdown will quality power to the Pi.

That UBEC is 3A and may be able to power your servos. With luck.

The Pi B takes less than 1.2A on its own, a lot less I think, and the camera module
a lot less than 0.25A (it would probably melt if so). Its the USB peripherals that mean
a Pi is recommended a 2A supply.

You claim 4 DC motors take 0.4A, highly unlikely, budget amps for this - what motors
are you talking about, what H-bridges?

[thiezn]

Thanks for the reply MarkT

So basically you think it's better to have two seperate battery holders, one for the H-Bridges and the other for powering the arduino, pi and directly connected sensors/servo's? I was hoping to have a single battery for my robot.

The UBEC is only intended to regulate power to my raspberry. I wanted to connect the arduino directly to the battery using a 2.1mm power plug and expected the arduino voltage regulator to be able to handle the conversion?

The two H-Bridges are based on the L298N chip and can directly drive two 3-30DC motors. Link to the specs is here

I'm using the motors that come with the 4 wheeled Smart Car Chassis kit, specs are mentioned here:

I've made a quick (and very rough!) sketch of what I was hoping to do and attached it to the post.

Cheers,
Thiezn