Miguel's Build Mods and First flight

So I managed to get a batch 2 kit from somebody that never had time to build theirs. As a disclaimer, I’ve never flown a paramotor before and have just started a course last weekend. I am, however, a EE and work in the RC hobby industry, so the mod’s that I have done will be mostly related to my experience in those fields.

My build has been flown once by my instructor for 8.5 min on 2x Bonka 6s 22000mah which had 10awg leads originally, but I cut them near the heatshrink and soldered 8awg wires in their place. After the flight, the switch and battery leads were just warm with the hottest thing being the two batteries themselves, but not even close to being untouchable.

So far, I only have a few mods, but I hope to have more additions later on.

In the RC world, it is somewhat known that long power leads to the esc increases inductance, which leads to higher voltage spikes on the ESC since the power draw isn’t continuous (PWM). This is the reason why the ESC includes very long motor/phase wires and short power supply wires, as the length on the wires for the motor side isn’t as critical.
Here is a very detailed RC groups thread addressing the issue

To be on the safe side, I added some 470uf, 100V caps to each of the motor power leads near the start of their respective connectors to my power distribution mess. They are somewhat separated from the ESC rather than being close to it for reasons described in the rcgroups thread.

Here is an image showing what I did.

Pre-charge switch:
In this image, you can also see a button on the bottom right in a blue 3D printed mount. The button is soldered in series with a 100ohm 30W resistor, and across the 2 contacts of the main switch. This is to address the arcing pointed out by others when initially turning the switch on after not running the machine for a while. The button is pressed until the first esc beep is heard, then I turn on the main switch.
Here are the parts I used
Button: https://www.mouser.com/ProductDetail/612-PB1973BBLKRILEF0
Resistor: https://www.mouser.com/ProductDetail/652-PWR221T-30-1000J
3D printed mount for button attached.
Pre-Charge Button Bracket v0.stl (69.0 KB)

Battery Lead replacement (for originally 10awg leads):
This is pretty straightforward. I cut the battery leads about 3/4" from the battery heatshrink wrap, and replaced them with 8awg wire. The solder joint was covered in liquid electrical tape, followed by actual electrical tape just to try to ensure that the leads never contact each other :slight_smile:


Servo Clips:
This is a pretty basic one. These clips are usually used in giant scale or just larger planes in general to help prevent servo connections from disconnecting due to vibrations. I used these for the ESC connections to the throttle controller, and the 5V connection to the throttle controller as well. You can kind of see them at the top of the first posted image.

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Question for you Miguel. Do the caps present any issue when charging the batteries? I know the chargers do an initial check of the battery before beginning and I wondered if the cap would confuse it.


The caps are part of the power distribution wiring within the OpenPPG unit, and not a part of the battery leads themselves, so they’ll have no effect on charging. Those EC5 connectors where the caps are soldered are the connection between the internal power distribution to each individual esc, not to the batteries. :slight_smile:

The 8 looks thinner - so much insulation on the 10!
Cheers, Patrick

I think Miguel didn’t read the document he linked to in an earlier mail, as he has fitted the extra capacitors some distance from the ESCs.
Here is a quote from the linked document:
Careful! too long battery wires can kill ESC

“How & where (not) to add extra capacitors
The capacitors compensate for the effect that wire length has on the ESC. Therefore all capacitors as close as possible to or on the ESC board, direct across plus and minus terminals.
Do not distribute them along the battery wires! (noise_suppression_101)
Capacitors near/on battery are useless, the battery itself already is a huge capacitor.
By distributing them along the wires between battery and ESC they will be less efficient, or even useless.
This would only add extra weight, take up extra space and it would only introduce extra points of failure. …”
Also, if anyone is thinking of adding capacitors to their ESCs, you would be stupid not to use low impedance low ESR capacitors.

And yes, it does look like Miguel’s idea of 8awg wire is different from the rest of the planet.

Hah, you’re right! I was following a spreadsheet linked within the rcgroups link that tells you how many capacitors to add based on your length and for what is more of a bus topology rather than a star topology as I am using. In this case, you’re right, I should be putting the extra capacitors as close to the esc as possible. Thanks for pointing that out, I’ll make that fix when I get the chance!

Also, I promise that is 8awg wire. The insulation thicknesses are a little different, and in the image, the wires drop down further from the start of the solder joint, so it might appear thinner than it is. My instructor flew with just a pair of packs, and there were no temp issues that other people were facing using the 10awg battery leads. This is the wire I’m using https://www.horizonhobby.com/wire--36--8-awg--red-cse011002800

Thats right. Important to note that the capacitor leads should be as short as possible to reduce additional ESR. Here are some decent caps https://www.mouser.com/ProductDetail/Nichicon/UHW2A471MHD?qs=sGAEpiMZZMtZ1n0r9vR22XrAbqid7dckOqVI%2bCgwqq3iye5iEvdlLQ%3D%3D

Also just noticed you posted that same link in the Lipo 6S thread.I must’ve missed that because I thought this topic had not been brought up until now!

Hello Miguel,

I don’t know why the ESCs couldn’t be mounted on that backplate thus keeping the power supply wires short and avoid messing around with lengthening wires and adding capacitors, I suppose it’s for cooling?

Right, cooling is the only reason I wanted them out on the arms. I cant think of any other reason you’d want to have to make the power leads longer.
After that one flight, they were barely warm being on the arms. That was also just an 9 min flight without a lot of continuous climbing so it could potentially get worse.
Cooling is arguably not as necessary as I thought it might be in this application, but I think I prefer the option of better cooling even if it means having to add more caps. I personally haven’t pushed the unit hard enough though to determine how much hotter the escs could get. The change between arms vs center plate is probably pretty significant as far as airflow/heat escape goes.

I wonder how modellers get on heat wise with these ESCs banged-up banged up in their aircraft, or whatever.

It can depend on the plane model, how you decide to build it, and how the esc is spec’d. A lot of them have gaps in the cowl/front of the fuselage that allows some internal airflow. Here is one particular build I did 5 years ago where the esc is literally mounted on top of the fuselage (blue block on the top left).

Also depends on how much money is spent on the build, and whether people care to be overcautious or not about overheating.
Also worth noting that planes wont normally be flying for 15+ minutes straight, and people are less likely to be over cautious since it’s not really their life on the line when they fly these models.

Got my first solo and 3 other flights in this weekend!
Looks like while the added 8awg section on the battery reduces overall heat buildup along the wires, it is still not good enough for the local heat build up of the 10awg section when continuously drawing high current, and using only 2 lipos.
My first flight was up to 200ft altitude and everything was perfect afterwards temperature wise. The hottest thing were the batteries themselves but they were just warm.
The second flight, I kept climbing up to about 400ft and the system shut down. I stayed over the landing zone so I glided down and landed no problem. After looking at the batteries, the small sections of 10awg wire had melted the plastic wrap over them on the battery, and one wire had desoldered completely (hence the shutdown).
I resoldered the battery wire (stripped it a bit more too for a better joint), and flew 2 more times in the afternoon with 2 sets of batteries instead of just one. Pushed it about the same amount as the failed flight with no issues. Batteries were barely warm after landing. I think I will stick to a minimum of 4 lipos from now on :slight_smile:


@MiguelFAlvarez, thanks for sharing the details of your build. I learned a lot and decided to make a precharge system as well. I think you may want to change the resistor that you are using on yours though. I tested my system with a 100 ohm resistor and found that with resistance that high the capacitors don’t precharge to a high enough voltage to prevent arcing. I could hear arcing inside the switch. I opened up the switch and could see pitting on the contacts caused by said arc. I am using a 22 ohm resistor now and I don’t hear any arcing. Maybe after several flights I will inspect the switch again.

Will have to try that, though I havent had any issues with the 100ohm so far. I usually hold the button down while I’m turning on the switch to at least hold the charge, and prevent the esc’s from discharging the caps completely.

What voltage does your controller read while holding the precharge button but before the main switch is flipped?

With a 100ohm resistor in the precharge I was seeing a difference of 10v and when I flipped the main switch I could hear the spark. It’s hard to hear but I could hear it. Then I opened the switch and could see pitting from the spark.

Since it is hard to hear you might have a problem and not realize it. It took 100 flights before my switch degraded enough to cause problems and then it melted 3 minutes into a flight. That was without any precharge at all though so you would likely get even more flights than I did before you realize the same problem.

With a 22 ohm resistor in the precharge there is only about a 2 volt difference between precharge and full on. I can’t hear any sparking with that resistor.

Please let me know if you see the same voltage difference as what I saw.

I see about 30 volts on mine, so pretty decent difference with fully charged. You might be right and I may just not be hearing it. With winter starting, I may not be flying anymore for a while, so it’ll give me time to open things up and take a look. I also saw your pre-charge switch in the other thread, and I really liked that! Think I’ll give something like that a go. Also digging your cable organization!

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