I’m not a electrical engineer, but the voltage drop might be because the unity is running (altho this is a bit of a steep drop).
Just to make sure, you are connecting all 5 wires?
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When I connected the 5 wires to the st-link, it lost the serial connection with the computer.
On the other hand, when I leave the st-link without wiring anything, I can create a connection from the computer.
Because that, I was checking first the power wires with the voltmeter.
That’s weird. Can you see anything what might be shorted near the connector on the unity? Also, did you buy a good Stlink from a reputable seller? There are some bad sellers around
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I have this one.
But I could return it and buy another one, anyway the led that has inside doesnt blink.
I can buy this st-link and it will be here at weekend. I think is the same as in photos above.
EDIT: I’m going to try wiring the GND with the ST-LINK, and the 3.3V from my adjustable power supply.
EDIT2: I connected the reflash pins to power supply, and it falls anyway.
From 3.3V before connect, to 1.52V when is connected, I think this have no sense, instead the focbox hardware is not right.
EDIT3: Yeah!
As I said, when I connected the power supply to Unity, the voltage falls. With the wires on and 1.52V, I forced to upload the voltage to 3.3V and the leds of unity turn on! w0w0w
Then I connect the ST-LINK and I’ve be able to upload the bootloader 
After that I connect the focbox to the battery (10S) and when I press the switch only the blue led goes on, and after that turn off again. At least, now something goes on, it seems that we have advanced something. I tried the USB-C, and there is no connection to the computer. Does anyone know what it means if just turn on the blue led?
EDIT4: 
I was trying to reflash the firmware again as I read in other post, but I get an error now.
Can not read memory!
Disable Read Out Protection and retry.
I can not write in the Focbox … 
That is weird, I don’t think it’s supposed to activate RDP. I’ve read somewhere that it might be solved by updating the stlink utility. Have you downloaded the utility from the official site?
You can try to connect the Unity to the battery (not to the motors), and use the STLink as normal without the 3.3v wire (do connect the ground!). The STLink might not be able to supply the power needed for the Unity. You might need to hold the power button for it to stay on, I’m not sure.
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Yes, I downloaded it from that website some days ago.
I was connecting the Unity to my adjustable power supply, and I tried too with the battery, it didn’t work anyway. I was trying too, holding the power on switch and the blue led went on until I release the switch.
I’m looking for Flipsky VESC, because I haven’t been able to eskate for a month… 
Thank you for the response, I love the forum!
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I know its been a while since anyone’s commented, but I have this problem and am unsure of a couple of things. On St’s Website there’s a 21$ tool and an 80$ tool, the 80$ tool has Digital Isolation and in unsure if that’s a requirement of the tool for it to work. That appears to be the only difference in the two tools. Secondly, I’m unsure how to hook the st link device to the board. I’m having difficulty understanding the depiction. Thanks for any help
Just thought I would update on my 4 wheel drive with 2 Unity build.
I ended up setting my board up as 2 completely separate, independent 2 wheel drive systems. So basically, I used 2 separate batteries, 2 separate controllers, and 2 separate receivers. then I paired both receivers wit ha single remote control. This seems to be the best way for me to set up a 4 wheel drive board.
Other key to success with this board is to keep the main positive and negative power wires between the Battery Pack and the Focbox Unity Controller to the absolute minimum length!
I’ll be back sometime in the future to talk about my thoughts on strategies for setting the variable values in the ESC. I think the ESC configuration is one of the least understood and challenging tasks in getting the most out of an ESK8 board. I bet there are a lot of folks out there who are just guessing what settings to use or maxing them all out, etc. and trying it out. But it would be nice to hear peoples theories and also have a complete list of exact numbers they use on their particular setup. I know this is partially black magic, but would be nice as a first time builder to find something like a recipe for pretty good performance for a similar setup…Or even compare someone else’s recipe to your own on the same hardware. Anyway, keep up the good work and ride safely as much as possible : )
@DSluijk Hey, my Unity will turn on but I cannot turn it off. I also can’t connect it app via BLE or the windows tool via USB-C. It says it can’t read the firmware version. So if I buy an ST-Link, I can re-flash my firmware?
EDIT: Thank you so much for this guide. Saved my ass!
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Hi, I’m not that active here anymore, so sorry I could not respond in advance. Glad my guide helped!
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Its great for redundancy like you have.
But you are missing 4wd traction and it work very nice on dual unity.
Hi,
My unity shows a flickering red led when i connect it. Is that normal?
I did everything but it won’t work. I even did a full chip erase.
Is my unity just total loss?
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That sounds like something is broken in software. Have you tried to follow my tutorial already? Don’t worry, as long as it is a software fault it’s not a total loss :).
Hi trying to do the trick but unable to find where do i connect rst pin on the focbox ? anyone could help me ?
Hi, did you take a look at this table?
so dumb i am , i read first draw reverse, thx
It seems I need to hard reset using the pin nr. 7 on the MCU
@eBoosted
You should have connected according to your first picture. The way you decided upon is wrong. Luckily the ground is on pin 3 in both your pictures so hopefully nothing broke. 