How to take your Gigabot Off-the-Grid

One of our values at re:3D is to provide 3D printing technologies to communities around the globe, many of whom don’t have the resources we take for granted.  Access to plastic feedstock, a consistent power infrastructure, and reliable shipping services have always been a requirement to play in the 3D printing space. We want to change that. One of the microsteps in this direction is to find other ways to power our 3D printer, the Gigabot, while still allowing multi-hour (and sometimes multi-day) prints to emerge from our 600mm X 600mm (2ft X 2 ft) build platform.

I started experimenting this past week using a 40W solar panel and a car battery, and had some success printing a small test print. I’ve gotten some questions since then and wanted to explain a little more about my setup, and also find out if there were any other (successful or not) attempts to take YOUR 3D printer off-the-grid.

MY SETUP:

Our Gigabot takes 110V or 220V mains power, but then immediately feeds that to a 24V power supply to power the motors, hot end, sensors, USB comm port, and display. The only part that makes use of the mains power is the heated bed (the one that can fry an egg).  Since using PLA as an input material usually eliminates the need for a heated bed, I started there.

Disconnecting the power supply completely, I wired the 12V battery directly to our controller board and internal cooling fan. I later learned that this cooling fan was a great audible indicator of voltage levels – but more on that later.  12V is at the very low end of what our controller board can take in, but the real question was how long could it print for?

THE PHYSICS:

I like to equate electricity to water coming out of a hose (like in this great tutorial from SparkFun), so to follow that analogy, I had to figure out if I could hold enough “water pressure” (voltage) to keep the controller alive, a large enough “holding tank” (car battery) to last for the entire print, while using solar panels to add enough “water” (power) to the system during the print.

After testing with a multimeter, I saw that the Gigabot draws about 5A at the most, and less than an Amp when idle (to keep the controller and comms alive), and on average about 3 or 4 Amps while printing (since the heating element cycles to maintain a constant temperature). Judging by the rating on my car battery of 70 Amp-hours, I could count on about 14 hours of power.

I should add that we often exchange Amps and Watts freely when comparing power levels. They are only interchangeable if the volts of the system remain constant (12V or 24V for Gigabot, 120V for USA Mains, etc.), since Power (Watts) = Current (Amps) * Voltage (Volts).

Or per the above analogy: Ability to Remove Mud From Car = Size of Hose * Water Pressure.

THE EXPERIENCE:

The solar panel I bought from Fry’s was impressive, but at 40W I know it wouldn’t get to the levels I needed, and I could only afford to experiment with one. Plus, pausing a print when the sun goes behind a cloud just isn’t practical, since it would leave many marks of semi-melted plastic along the way, and the stepper motors would lose their homing location. I knew that the final solution would at least rely on some battery power.

We all know what happens when our car battery is suffering when you try to start it: the lights get dim, you turn off everything electrical, and pray that it turns over and you can get home that night. Instead of a gasoline powered motor and alternator to keep the battery alive, I had a solar panel – and it had to last the entire print. So I had some questions – and like any former space station flight controller, I took lots of data.

THE QUESTIONS:

Would 12V be enough to power a system that we have been used to operating at 24V since the very early days? Would my Gigabot’s hotend pull down the stepper motors too far on battery power and affect the success of the print? Could I use all of the available power in the car battery to make a large enough object without any transient errors? Could I turn on and off the solar panel or battery charger during a print without interrupting it?

THE RESULTS:

At first things looked (and sounded) gloomy. The first few attempts failed, and it seemed that the battery just didn’t have enough power to drive the hotend, motors, and electronics to keep the voltage levels high enough. Even the fan noise sounded sickly – a lot worse then when I had it set up without the multimeter.

firstpicoffthegrid

The multimeter! That was it!!

I had wired my multimeter in line with the positive line off the battery to read a super accurate space-rated amp-draw during the entire print. I had wanted to measure exactly how much was going in and out of the solar panel, and the battery. The measurement itself was actually resisting the flow of electricity (the equivalent of bending the water hose to hear if water is rushing past the fold in the line). Once I removed the multimeter and tracked only the voltage across the battery terminals, I was able to get over 13 hours of continuous printing time out of my Gigabot – enough to print this 300mm (12-inch) tall vase! Here are the (manually entered) data points for that one:

secondlinkoffthegrid

The solar panels are pretty straightforward, and work very similar to the battery charger I plug into the wall, so for the purposes of my experimentation in the garage, I’m alternating printing on battery power with a charger on/off, solar panel connected/disconnected, at varying voltage levels of the battery. I think I have found the limits, since my prints start failing at just about 11V on the battery now.

Also, ever since I automated my data taking process, I get much more sleep at once, without needing to wake up for data takes with pen and paper (and help from Google Sheets). Check out the new and improved version with a little help from plotly!

gigabot_printing_a_vase_on_battery_power

An interesting part of this method of gathering data is that you can start to see the cycling of the cartridge heater very clearly as the extra current draw pulls the battery voltage down each time the hotend is full-on. This will be useful in tweaking my PID values no doubt, and could also lead to better methods of insulating the hotend so it doesn’t need to heat up as much, thereby saving valuable amp-hours!

NEXT STEPS

Clearly there is a little more work to do before we have a brownout-proof or solar-ready Gigabot out of the box, but I think these experiments prove it’s within the realm of possibility to create 3D objects anywhere – given a robust enough printer, and a light bulb’s worth of energy and imagination.

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