Zumo Charging: A Stupid Question

So, I’m currently in the very preliminary stages of designing a set of robots using the Zumo chassis/shield as a base. Ideally, these bots are going to be left ‘unattended’ (art installation style) for long periods of time, so I’m hoping to code them so that they seek out a charging station and charge themselves up using some plates attached to their backs. Is this possible/a good idea? Will trying to charge NiMH batteries while the Zumo is switched on cause explosions or dead boards?



We have not tried that, so I do not know if it will work. If you do try charging the Zumo while it is still on, I recommend taking a couple precautions. You might want to keep the power consumption on the Zumo low when you are charging it, as I suspect this might affect the charging cycle of the charger. You might also want to be careful about the charging current, as that affects the voltage used to charge the batteries (even though you might want to keep the current low you will need to make sure the charge current is above the current consumption of the Zumo). Without any modifications to the Zumo, the voltage across the batteries should not exceed more than about 7.5V.

If you do try it, I am very interested to hear what you find out, and am definitely excited to see a Zumo charging station.

- Grant

So, an update. I’ve tried charging with the iMAX B6AC that Pololu sells, while the Zumo was ‘on’ - works great! I tested charging at 300mA, 600mA, and even up to about 1400mA works fine. Running the motors while charging seemed to have a negligible effect on charging status, though it’s probably not the best idea to have them running continually while charging. Seems safe enough to have them running for a few moments while the robot finds it’s position on top of the charging pad (which I haven’t actually built yet), and as it leaves.

Right now, because the B6AC doesn’t seem to have an option for auto-charging – automatically recognizing that a battery is connected, and beginning a charge cycle until battery full – I’m researching some other chargers (Tenergy’s 01006 2.4-7.2v charger is in the mail to me) that are ‘dumber’ than the B6AC. Hopefully, using the battery voltage level jumper, I’ll be able to let the Zumo recognize when it’s both low on charge, and should seek out a charge plate, and when it’s been fully charged and can safely leave the charge plate.

I’m also working on making an adapter board/shield that would allow for using a PJRC Teensy 2.0 (and maybe eventually a Teensy 3.1) instead of an Arduino Uno or Leonardo. Currently, the board has sockets for a front-facing PING ultrasonic rangefinder, and a rear-facing IR distance sensor, while leaving almost all the other Zumo shield pins unused. Due to some of the timers being on different ports/pins on the Teensy, some of the library code had to be tweaked to make it work (buzzer is now on pin 12, though still PORTD7, motor PWM are on pins 14/PB5 and 15/PB6, switch on pin 23/PD5, BUT, the SCL/SDA lines no longer share output with other pins). It also includes a 3.3v regulator and a 5v regulator, as the Teensy has no onboard regulators.

Would anyone be interested in a more general Teensy convertor board for the Zumo? If I have the time I would not be opposed to making a general-purpose adaptor board. I chose to use the regular Teensy 2.0 because it’s very small, but a Teensy ++2.0 board has a LOT of extra features beyond an Uno or Leonardo (namely about 4x the program memory, 4x the RAM, and 4x the EEPROM. And 48 GPIO with 8 Analog input pins) The Teensy 3.1 has 64k RAM, 256k program memory, and runs at 72MHz - an enterprising individual could probably do some very interesting spatial mapping stuff with that much memory!

Thanks for sharing what you found out. That also sounds like an interesting project for the Zumo, and I would love to hear more as your project progresses. By the way, I am not sure if you are making your own shield or making an adapter for our Zumo shield for Arduino. It would probably be easier to make an adapter, but the system would be more elegant with a single new shield (made for the Teensy).

- Grant

At the moment, i’m making an adapter that will sit between the Pololu Zumo shield, and the PJRC Teensy. The adapter board will include a 5v regulator (for the Teensy, and Zumo components) and a 3.3v regulator (for other zumo components). At the moment, it’s all through-hole components - really just the two regulators, 4 small decoupling caps, and some female header sockets for the Teensy and sensor points.

I didn’t think it necessary to re-invent the wheel and design a whole new Zumo Shield that doesn’t fit the Arduino Shield ‘standard’ - the work you guys have done is very solid and well tested, and most of all all the libraries are already built for it (and only need minimal modifications to work on Teensy, so far!)

That said, I haven’t looked too much into making the adapter plate work for both the Teensy 2.0, and the Teensy ++2.0. They have similar-enough footprints that --physically – it might work to have a single adapter that lets you use either board, but I think the hardware timers and ports are in different configurations so it may not work nicely without some special jumper pins magic. :smiley: