this post was submitted on 12 Dec 2023
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Asklemmy
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Well, you can have one now, if you want!
I usually build around the Pi pico as a brain, L9110 motor controllers, N20 DC brushed motors, and a standard 18650 lithium cell, and some generic BMS + switch mode voltage converters. From there you can either add sensors and make it autonomous (more challenging), or just control it via your smartphone (easier). You can either make it omnidirectional with mecanum wheels, (more expensive) or turn/forward/back motion only with a differential drive.
Along the way you'll learn to solder and code, if you don't know already. It's a suitable beginner to intermediate project. Most of the work is knowing what cheap parts work well together (read and interpret lots of datasheets), actually assembling and using the robot is pretty easy. Usually I can keep cost under 50$, but parts are cheap here -- certainly under 75$ in the West though.
Well damn... Now I have another project!
I have a Pi 3 sitting around that I used to use for Octoprint, but when I rearranged my workstation I didn't have room for the monitor so I just went back to SD carding it. I picked up an end of service Chromebook that I was going to dump Linux on and make it my new print server, so the Pi is free.
I'm going to end up with my own little astromech Droid!
That's a bit overkill in terms of processing power, but it will definitely work! It's actually powerful enough to do machine vision and mapping!
One thing to remember is that the current draw for the Pi 3 will be much higher than the Pi Pico. Some students have had battery issues using motors + the Pi at the same time. They got the batteries in a sketchy industrial market here in VN though, so they were definitely not rated for very high current. This is one reason I use the Pi Pico and low power 6V motors -- it runs all day of a single very questionable lithium cell. Boots in milliseconds too, vs. much longer on Raspberry Pi + Debian, at the risk of comparing apples and oranges.
Another thing that was annoying, is to remember to put nonpolar capacitors across your motors if building your own motor controllers (most modules you buy will do this for you). Otherwise, noise from the e.g. brushed motors will probably make the Pi reboot constantly. I had this problem pretty bad -- it worked fine hand-soldered but when I got the boards from the factory it would fail often unless I put the caps in.
Anyway, if you're short on time and want to get the project done, there's also a thing called the Motorshield that will let you very quickly build a robot from the Pi you have. There are also LiDAR shields if you want to try mapping and fancy autonomous navigation. If you want cheap, you can't beat this motor controller module though (and you'll just need 1 for a differential-drive rover):
https://hshop.vn/products/mach-dieu-khien-dong-co-dc-l9110
You can generally find it anywhere in the world!