How to Power the Project

CoderDojoGitHub / robot1-series

Our first series of hardware and software hacking classes.

MIT License

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How to Power the Project #6

Open skylar opened 10 years ago

skylar commented 10 years ago

This is a hard part. Reading up on this is really fun though and it makes very obvious why RC cars really eat up the battery!

This page is a good starter:

https://learn.sparkfun.com/tutorials/how-to-power-a-project/remotemobile-power

skylar commented 10 years ago

So, first off, we have to figure out how much power the project draws. Some sample parts:

Arduino Yue ~270-310mA
Spark Core ~150mA (WiFi on), 10mA (WiFi sleep mode)
Motors ~1.2A (~330mA per coil), as supplied by the driver (12V preferred, less means less torque)
Servo ~75mA

So, power for the logic is negligible. Most of the power goes into the stepper motors. We're looking at maybe 1.6A as a draw for the Yue-based version, and maybe under 1.5 for a Spark core.

So, we could power the bot for a little over 90 min on a 2200mha battery pack.

The driver boards seem to do better the more voltage you give them (up to 45V). They can charge the coils faster and deliver up to 12V to the motors. However, they seem to work fine with as little as 5V, with the side effect of less torque.

skylar commented 10 years ago

I'm looking into various ways we could wire in power from a battery. A couple considerations:

on/off switch?
the battery should be easily disconnected for charging (and/or offer an on-board circuit for charging via plug/USB, etc.)
we need both logic power and engine power. An A4988 with voltage regulation (like the Big Easy) offers onboard power sources at 3.3A and 5A, making connection a cinch.
In high-power applications we need to protects against power-up voltage spikes. Again, the voltage regulating motor drivers protect against this. If we used a standard driver, all we need to do is put a 100uF resistor across the power supply to the board(s).

skylar commented 10 years ago

One option for power are these packs. 8.4 V, 2200mA.

http://www.pololu.com/category/108/8.4-v-nimh-battery-packs

Also, we could wire two in parallel to get over an hour of power. Another option is to use off-the-shelf AA batteries, and pack them into 2-3 battery arrays in holders:

http://www.pololu.com/product/1156

skylar commented 10 years ago

Another option might be a big pack lipo pack like this:

https://www.sparkfun.com/products/11856 https://www.sparkfun.com/products/10470

Downside seems to be a special charger for the multi-cell packs used in these blocks.

skylar commented 10 years ago

My setup so far. 12V / 2A input which splits out 5V power to my board via a voltage regulator (orange wires).