Assembling the Electric Crawler (Part 2)
Introduction
I am making a GPS electric crawler.
I am using the CuGo V3 Complete Kit as the electric crawler body and the Holybro PixHawk 6X as the automatic control computer for the crawler.
Currently, I am connecting PixHawk to a Windows PC and configuring it. In order to mount PixHawk on a crawler, I checked the connection of the CuGo V3 complete kit.
Crawler connection
The battery in this kit is a 24-volt 6Ah iron phosphate (LiFePO4) battery. Iron phosphate batteries output 3.3 volts per cell. Meanwhile, the motor used here is a 45-watt one. The transmitter and receiver are a set of MC-8 and MR-8 from Kondo Scientific.
Therefore I checked the wiring of the crawler and found the following. The FET switch had the CuboRex logo on it.
The power supply for the MR-8 radio control receiver is 3.0 to 6.6 volts. The MR-8 has a total of nine pairs of connectors: outputs A to H and the power supply BAT. Each pair of connectors has three pins: positive, negative, and PWM output. I couldn’t understand why it worked without being connected to the BAT, and why it worked without a DC-DC converter.
When reading the MC-8 and MR-8 manuals, it says:
RC car ESCs can output MR-8 (receiver) power by connecting to the running power supply. When using an RC car ESC, do not connect a power supply to the BAT terminal.
This ESC appears to have a built-in DC-DC converter that converts from 24 volts to 5 volts. This is a know-how product, as they provide a FET switch unit and select an ESC that can output 5 volts.
Powering the PixHawk
To supply 5 volts to the PixHawk from this 24 volt power supply, I will use the PM02D that I purchased at the same time as the PixHawk.
The PM02D comes in two ratings: the discontinued Low Voltage 2S-6S, and the current High Voltage 2S-12S. I couldn’t figure out what the difference between these two ratings was by looking at the homepage, but 2S-6S means a maximum of 6 cells (3.2 volts x 6 cells = 19.2 volts), and 2S-12S means a maximum of 12 cells (3.2 volts x 12 cells = 38.4 volts). 2S-6S would result in overvoltage. This rating is supposed to be marked on the back, but there was no rating mark checked on my PM02D.
On the sales page of the place where I purchased it, it was written:
Starting from Nov 21, 2023, pixhawk 6x combo set will come with PM02D-HV instead of PM02D-LV
So I decided to believe that my PM02D is rated 2S-12S.
So I connected this PM2D after the FET switch and connected the PM2D to the PixHawk 6X. The wiring is as follows.
I was able to successfully power the PixHawk.
It may be tempting to try connecting the PixHawk to a PC in this state, but this is dangerous. If you supply 5.2 volts from the PM2D and 5 volts from the USB port, a 0.2 volt potential difference will occur between the internal power terminals. However, since the power line has low resistance, this line may generate a lot of heat. I will check whether the PixHawk has a circuit to avoid this situation.
Conclusion
I looked into the power supply of the CuGo V3 complete kit. I was glad to find that I could power the PixHawk 6X through the PM02D. I’ll start assembling the GPS electric crawler little by little.
Related article(s):
- Assembling the Electric Crawler (Part 3) 21st October 2024
- Assembling the Electric Crawler (Part 1) 11st October 2024