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Rover build

Posted: Sun Dec 17, 2017 1:07 am
by gjs31

Looking for some feedback on my newbie rover build on a Raspberry Pi 3 vb, particularly around power.

Have a simple chassis with four of those generic yellow motor gears (3v-6v I believe). These are driven by two L298n motor controllers and powered by two sets of 4xAA nimh rechargables, so 4.8v per set of two motors (Rpi is not providing power to the L298n boards).

RPi is running off one of the LiPo RPiPowerPack v1.2. This pack is powering the pi, two ultrasonic sensors, a PCA9685 servo board (servos are powered separately by 2xAA batteries), and an IR obstacle detection module.

Next additions to the rover are going to be a RPi camera (powered from the lipo), a simple pan/tilt arm coming off the servo board and AAs, and a simple gripper arm (single servo). Overall aim for the setup is to experiment with autonomous driving, Open CV, a second pi as a wireless touchscreen controller, and other things I haven't yet thought of.

What I'm trying to figure out is if this is a good power setup, using AAs and the LiPo board? Or would I be better off going down the LiPo path to power the motors/servos?

After I have it all running the way I want the next stage will be upscaling to bigger chassis and therefore bigger motors, at which point I'll likely be reconsidering the power setup anyway.

Thank you!!

Re: Rover build

Posted: Sun Dec 17, 2017 10:01 pm
by OutoftheBOTS
Sounds like a way cool project.

I have done lots of trailing different types of batteries the AA type tend to be the worst performing of all as they r very old school tech. Lithium type batteries are far better. Generally for the motors I use a RC Lipo battery as they r very cheap and can discharge at way higher rates than needed for your little motors.

I generally run my robots that r similar to the needs of your robot with just 1 RC 2 cel 7.4v Lipo battery and a couple of DC to DC set-down buck converters. I usually have a little buck converter stepping the battery down to 5v for the RPi and a second buck converter to step down for the motors and servos. Depending upon the buck converter used and the amps needed for the servos and motors you many need to find a converter that can handle the needed amps.

Also a note. You are using a L298n as a H-bridage. All components aren't 100% efficient and have some power drain. The L298n is designed to be able to drive much larger motor than your using so it is very power hungry due to it's size and its forward voltage is 2.7v (i.e it eats 2.7v at what current it going through it)

Re: Rover build

Posted: Mon Dec 18, 2017 5:07 am
by gjs31
Thanks for the reply.

I actually just last week ordered 4 of the L9110s modules to switch out due to the drain from the L298N ones as you mentioned. Will keep those for when I scale up.

Is it safe enough to split the power from a single Lipo into 2 motor bridges, servos, pi etc, for that matter a stack of AAs? I have set it sup the way I have so that each component has its own power source.

Re: Rover build

Posted: Tue Dec 19, 2017 10:28 am
by OutoftheBOTS
The RC Lipos are very high amp batteries most are capable of up to 60amps at 7.4v (see the gauge of the wires coming out of the battery). For your whole robot it would be lucky to draw a few amps so the RC Lipos will power everything not a problem.

For most of my robots I find space to be at a premium so try not to use several sets of batteries and just use the 1 Lipo.

You will need to run separate circuits off the battery of the electronics and the motors as the power spikes from the motors will upset the electronics. As I said I have a separate little buck converter for each item that way they r on different circuits. If you run 5v into the RPi then the RPi will further regulate it down to 3.3v with very low ripple.

Google mini360 buck converter is a great little unit that takes up very little space. Most seller advertise it will handle 3amps because the chip is rated for 3amps but most manufacturers use a really small inductor that can only handle 1.5amps to keep the size down so this limits the unit to about 1.5amps even though the seller say 3amps.

Re: Rover build

Posted: Thu Dec 21, 2017 10:13 am
by gjs31
So please correct me if I’m wrong, but can I simply go Lipo to splitter, then one of the splits to buck to motor controller, and off the other split to buck to Servo controller? Will this complete the grounding for the circuit?

I have a Lipo supply for the Rpi, which I’ll stick with.

Thanks again.

Re: Rover build

Posted: Fri Dec 22, 2017 11:01 pm
by OutoftheBOTS
Yes this is correct.

Re: Rover build

Posted: Fri Dec 22, 2017 11:59 pm
by gjs31
Awesome, thank you.

Have started planning for the next build, going to slowly buy up on actobotics parts and make a decent sized 6 wheel rover.

Re: Rover build

Posted: Thu Dec 28, 2017 8:42 pm
by Guneshs
Just for your reference ,
i am attaching a circuit schematic of my robot.
Good luck :)
Screen Shot 2017-12-26 at 7.12.55 PM.jpg
Screen Shot 2017-12-26 at 7.12.55 PM.jpg (202.07 KiB) Viewed 1004 times

Re: Rover build

Posted: Fri Dec 29, 2017 5:10 am
by gjs31
Thanks for that, nice to know that I am on the right track and not about to fry my second pi (being super cautious now).

So from that diagram the full voltage goes to the motor controller, and the stepped down 5v to the servo controller?

Re: Rover build

Posted: Fri Dec 29, 2017 6:27 am
by Guneshs
Good to know it was helpful to you.:)