I’m pretty sure I’ve seen a few VEXU teams use Raspberry Pis on their robots in the past. Hopefully some of you are on the forum. How did you power it considering it requires exactly 5V and a decent amount of current? Is it best to use a dedicated 7.2V battery and a voltage regulator? And then is it best to power off the I/o pins or through the microusb port on the pi? If anyone has specific part recommendations that would be great
We used one of these
We had a dedicated battery run it but that battery could have had more components on it as well. The 5V line on the cortex would not be a good power source for the pi.
We powered off the I/O pins but if you had a USB output on your converter you could just as easily use the microusb port.
It wouldn’t be a good source of power, no, but apparently UART lifts
We built our own power supply and just chopped off the female end of a USB A-A connection. You could chop off the end of a micro-USB cable, but then we can’t repurpose the micro-USB later. Bad idea when you assume the power requirements are the same as older RPis. We’re probably gonna use what WPI uses next year if we decide to do something with a Pi.
We did have an embarrassing flaw during practice. So there is an off and on button on the converter I linked. We had our converter low to the ground. And had protected it but our wall had a hole in it. A star we backed into hit our off button. We felt pretty stupid.
There isn’t much risk of a sudden powering down if you have something like Cortex or Arduino that use flash memory as the read-only resource. When the power comes back up - they just re-start from the beginning.
However, Raspberry is almost a full blown computer and is using its flash storage both for read and write (not sure about other OSes, but Raspbian writes back to SDHC all the time). Even though the file system is supposed to be journaled and fault tolerant, you never know…
So, WPI1 does a very right thing by running Raspberry Pi off a dedicated battery. Even if Cortex resets mid-game it shouldn’t affect Raspberry’s power. If you have to share the battery with the rest of the robot you may need to do something special.
Since you cannot use additional batteries in VRC, you may want to research some projects, where people use “supercapacitors” to give Raspberry Pi few more seconds to run and a safe way to shutdown in case of the power failure. Supercaps are usually low voltage, very high capacity, need a special charging circuitry, and take forever to charge.
Alternatively, I’ve bought a large audio capacitor (22,000uF @ 63V) and will try to experiment how long PiZero could run off it before voltage drops too low. To do that I am planning to use DC-DC boost converter to step up source voltage to 50-60v and then step it down to 5v with a (buck) switching converter, similar to what @tabor473 linked above. The tricky part is to find one that takes high input voltage.
^^ you should keep that charging voltage under 48 VDC, for safety.
Thanks for your help guys
You can also lower the power requirements for a Raspberry Pi 3 by slowing its clock speed. The Raspberry Pi 3 is a 3.3 Volt device but it uses a lot of current. One way to power it is to get an efficient 3.3 Volt Regulator and run it off the 7.2 Volt battery.