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Feb 21, 2019, 06:41 PM
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UC4H : Son of FrankenSolo UC4H Powermodule

I received all my UC4H modules from Jani at JDrones and some modules OlliW built for this project. Thanks, OlliW! I'll use a UC4H V2 Powerbrick to power the system. The Universal Modules for GPS, Serial Bridge, Mavlink Bridge, LED Notify and Display will finish off the system. I'll use OlliW's UC4H Kiss 32A ESC carriers but I could use Universal Modules for the ESCs also.

I suppose the place to start a new build is the power supply because everything depends on reliable clean power. One of the problem areas and points of confusion in APM/Pixhawk builds over the years has been supplying power. The flight controller is a flying computer with sensors. In order to operate it needs clean reliable power to stay working and to evaluate its sensors accurately. So you don't supply power to your flight controller from a BEC on your ESC. Those voltage converters were made for simple devices on airplanes, not the rigorous requirements of a flight controller. Also, we can't power everything in the whole world off our flight controller power module. So just don't do it. Use a separate voltage regulator for other devices that need significant power. A flight controller pulls a few hundred mils so don't think about powering a 1 amp 5v led strip with the flight controller's power module.

The next very important aspect of a flight controller power module is to be able to monitor the power we are using to estimate our available flight time. We would like to know as accurately as possible how much power we have left in the battery so we don't unexpectedly run out of battery power and fall from the sky.

The problem with the original 3Dr power module, and its subsequent clones, is that the technique for measuring power used is fairly crude. The original design uses a shunt resistor. What this means is that a very small value resistor is put inline with the power flow and the voltage drop across the resistor is related to the power going to the rest of the system. It then sends an analog voltage of 0-3v to the flight controller where it uses an onboard analog-to-digital converter to "read" that voltage. The computer then scales that voltage to the actual voltage and current at the power module.

Low value resistors in cheap electronics may not be the best quality. If the resistor is not the exact value that the calculations depend on, the readings will not be correct. If the resistor heats up under load, it may not be linear and the readings will not be right. You get the wrong readings and you think you have more battery left than you really do and you fall from the sky. Because the power is actually flowing through the sensing device, if anything goes wrong with it, it can cause your whole power module to fail and you fall from the sky.

Then Chris Mauch came along and he designed a power module that used a Hall effect device. This device acts to sense voltage and current by using a magnetic field that is generated when current is flowing through the power module. The advantage is that the Hall effect device is not directly part of the circuit so if it fails the power does not stop. But you still send the analog voltages representing voltage and current to the flight controller. Chris calibrates each one of his products and you get a chart to help get accurate readings.

OlliW uses a hall device with the UC4H Powerbrick (UAVCAN Power module) but he took one more step. Because all CANbus devices are "smart" and have a microproccesor onboard, he can take the measurements and other information about the power module and send that information in digital form, via UAVCAN meassages, to anything on the bus that wants the info, including the flight controller. So now the flight controller does not have to change analog voltages to digital and calculate the voltage and current coming from the power module. The UC4H powerbrick does all the heavy lifting for the flight controller.

The UC4H powerbrick supplies clean 5.3v power at up to 2.5A to your flight controller and provides two 5.3v outputs for other things that need power.

One thing that needs power is the CANBus itself. Somewhere in the CANbus there needs to be a supplier of power. The flight controller can supply power to the CANbus but, like supplying power to power hungry peripherals, it is best to be supplied by its own source. It is especially a problem because most popular Pixhawk-type flight controllers have a current limited 5v supply to the CANbus which triggers at a fairly low .5a to 1 amp. If you hit this trigger, by pulling too much power, your CANbus goes away and you end up falling from the sky. Since I plan to have a full set of UC4H CANbus devices I will use one of the UC4H Powerbrick aux power outputs to power the CANbus.

Because this project is the Son of FrankenSolo, I am once again using a Solo motherboard. Why? Because I get a Pixhawk cube flight controller, an IMX6 co-computer and a HD Video/RC control transmitter all on one board that costs me $50. But that means I need to supply at least 12v to the Solo mainboard. I am therefore using a power distribution board that has its own 12v power supply to use for the Solo mainboard.

The battery power comes in to the UC4H Powerbrick where it goes to the 3-in-1 PDB. Power to the CANbus comes from one of the 5.3v external power outputs of the UC4H Powerbrick. 12v power goes from the PDB to the Solo mainboard. Battery power is distributed to the ESCs from the PDB.

First, I do continuity tests to make sure I didn't solder anything that shouldn't be soldered together. Then I test the power module with the SLCAN UAVCAN monitor. I make a mini CANbus network with the UC4H Powerbrick and the SLCAN. I plug the SLCAN into my Laptop and connect, which then allows me to monitor messages going across the UAVCAN bus. I power up the UC4H Powerbrick and look for messages from it. I check all the output voltages and, if everything looks good, next time I connect the Solo mainboard and see if it boots up.

Please note the soldering on my photos is a good example....of how not to solder. My basement workshop is cold and it is hard to get a good shiny solder joint. At least that is the best excuse I can think of.

Here is the power section of the frame with the UC4H Powerbrick and the 3-in-1 power distribution board.

I'll be using a Titan 10.5ah 22.2v 6s3p 908gram Lithium Ion power pack which is much lighter than an equivalent Lithium Polymer pack. I am hoping to get 30 minutes of flight time with the gimbal and Ricoh GR camera.

Next the flight controller
Last edited by mike_kelly; Apr 27, 2019 at 09:41 AM.
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