Challenging Solder Project - RC Quadcopter Related - Page 1
Forum section: electronics / beginners

author: Yardstick
author_rank: Contributor
timestamp: March 13, 2017, 06:58:23 pm
content: I have an interesting challenge (for me) that I'm hoping someone can help with and that I hope will have some relevance to others, maybe for other purposes.I am putting together a quadcopter with a flight controller (FC) that doubles as the power distribution board (PDB) and does a few other functions that aren't relevant to the reason I'm posting (see attached image). The PDB portion of the FC consists of the two large pads next to the large holes (large holes are for power input connector from a battery). The function of the PDB is just like it sounds, it distributes power from the battery to four electronic speed controls (ESCs) that each drive brushless motors. Those large pads carry through to the bottom of the PCB, so both sides can be used to distribute power from the input to the ESCs. These things can pull a lot of power. I am flying with 4S, 1550mah, 75C batteries. For those who are not familiar with these batteries, that translates to a battery that puts out 14.8V nominal and is capable of 116.25A continuous discharge rate. The ESCs I am connecting to this PDB section are rated for 35A continuous and have 16 gauge power wires. They also have smaller ground wires for each signal wire on the ESC. So I have four 16 AWG wires and four 24-ish AWG wires that need to get connected to the negative side and another four, 16 AWG wires to connect to the positive side of the PDB.My current plan is to solder half the wires to the bottom PDB pads and then solder the other half of the wires to the top of the PDB pads. I am concerned that the heat of soldering to the top side will release the wires on the bottom side.I'm interested in any suggestions or other ideas people here may have. I have done quite a bit of soldering, but this is making me feel like a beginner again!

author: james_s
author_rank: Super Contributor
timestamp: March 13, 2017, 07:40:19 pm
content: It can be tricky, what you need to do is use a proper temperature controlled soldering iron with a large enough tip and make the joints as quickly as you can. If you still have trouble with the solder on the bottom melting, try resting the bottom joints on a moist paper towel or sponge, that will suck the heat out and keep that solder from getting too hot.

author: Yardstick
author_rank: Contributor
timestamp: March 13, 2017, 08:05:21 pm
content: That's an interesting idea. I did something similar when soldering copper tubing to some ball valves -wrapped the ball valves in a wet cloth to pull heat away from the teflon ball seat/seal. I should have plenty of heat and good temp control with my Hakko FX951 and one of the bigger tips I got with it.

author: tooki
author_rank: Super Contributor
timestamp: March 14, 2017, 06:30:26 pm
content: Why not use crimped eyelets and bolts?

author: james_s
author_rank: Super Contributor
timestamp: March 14, 2017, 06:44:00 pm
content: Weight and vibration are potential issues. Crimped connections are fine but I avoid having to screw things like that together. You can also solder female bullet connectors to the distribution board to make it easier to replace ESCs if necessary.

author: TheDane
author_rank: Regular Contributor
timestamp: March 14, 2017, 07:16:50 pm
content: Quote from: Yardstick on March 13, 2017, 06:58:23 pmI would omit the PDB function, and solder the wires together directly, creating a battery to ESC controller network - the currents are high pulses, as you are aware - and high fast currents tends to create large magnetic fields, that could easily influence your onboard devices such as compass or cause ripple voltage on the µP supply. Caps over the +/- inputs of the ESC's might better things, as can distance, but you can't cheat nature.(Voltage=Current change over time in an inductor -https://www.physicsforums.com/threads/deriving-v-t-l-di-dt.679814/)If not possible/desirable - I would solder all wires together on the bench, creating one huge large round sausage of the large wires - which is then connected to the board through either a mechanical way or by soldering. (Solder breaks way too easily when moved repeatedly, so strain relieve or experience cold solder joints)Do the controller have dedicated signal/power/ground pad for the ESC's - if it does, make sure you don't get ground-current-loops connecting everything together.The board is through holed extremly well, which not only transfers electrons but also heat (both is essentially 'just moving energy' - ever seen an electron?) Good luck on soldering both sides, as I would also suspect the solder job on the other side to go bust the second the solder flows on top.

author: Yardstick
author_rank: Contributor
timestamp: March 14, 2017, 10:40:02 pm
content: When I first saw the suggestion for eyelets and bolts I wondered if tooki saw the picture.Then I realized there are those big holes for the main power connector there. Still, the name of the game here is to keep things as light as possible, so connectors and fasteners are out.TheDane: The battery needs to power the FC and the ESCs. I thought about bundling all the ESC wires together and taking one 12 AWG wire from there to the PDB pads.The manufacturer provided a capacitor to solder across the PDB pads presumably to help with current pulses or voltage drops.The FC has signal pads for each ESC, but the signal ground is the same as the motor ground (at the PDB section). Couldn't I just run the small signal ground wire to the ground side of the ESC and only have one signal wire coming back to the FC? There are other power pads for regulated 5V and 12V outputs.Quote from: TheDane on March 14, 2017, 07:16:50 pmThat's what I'm worried about, but people seem to think it can be done.

author: james_s
author_rank: Super Contributor
timestamp: March 14, 2017, 11:16:50 pm
content: You can usually get away with only the signal wire from the ESC to the FC, as long as your grounds are good. Ground loops can be a problem but normally it will work. If you do use the signal ground with the ESC it should go back to the FC, not to the PDB.The EMI issue is a problem, I was never able to get a compass to work reliably on small multirotors, it's really only practical on larger stuff, maybe 300mm frame or bigger and placed on a small mast up away from the other electronics. Small multirotors are best flown in acro mode with a basic FC IMO.

author: Yardstick
author_rank: Contributor
timestamp: March 14, 2017, 11:38:17 pm
content: This is a racer/acro quadcopter so it isn't loaded with too many sensors. It's only ~210mm motor to motor and will use 5" props. Should be quite the powerhouse.Is EMI that much of a problem on the battery side? I can imagine it could be at the ESCs since they send high current, fairly high frequency pulses to the motors. It's probably a good thing I moved away from the 4-in-1 ESC solution. It would have been stacked under the FC. This FC also had an integrated first person view (FPV) transmitter in it. Those run at ~5.8GHz.

author: james_s
author_rank: Super Contributor
timestamp: March 15, 2017, 12:57:46 am
content: I don't think you'll have too much difficulty, it's only really an issue with a compass. Video can be a challenge but not insurmountable, generally attention to grounding and some filtering on the power to the Vtx will solve that.

author: TheDane
author_rank: Regular Contributor
timestamp: March 16, 2017, 12:54:07 am
content: I have done some research into drones, but currently lacking batteries - which has halted my drone flying project.I have worked with high power switching mosfets, which ESC's essentially are - DC in, 3 phase output to the rotor engine.There are written loads on the matter of ground currents, and it is a hard concept to master completely. Practice makes perfect, or at least running good enough.When the frequencies are low (kHz), and the currents high/pulsing - I often get most design ideas/precautions from thinking the wires as the transmission line in my car, a transformer as a gearbox (here the ESC's) and the wheels/rotors spins. A shaft can go through something, if shielded well enough, and out the other without problems.HUGE & HEAVY- Something I don't want to be close to unshielded.Electrons are lazy, and take the easiest way on their electrical way - but they're also taking the hard way + the extremly hard way + sometimes impossibly hard way. Oh, they also love being paired - wire wise, so twisting +/- minimizes the EMI emissions quite effectively. Good for EMC compliance, less good for design looks, manufacturing and breaking during a crash - insulation tearsI recommend running the high pulsing power train/bus-bar very much separately from the flight controller/RF(high-power away from flight controller)/Videocamera(also away from high power RF)/sensitive stuff - wrapped in Cu foil, a custom built flexible Faraday cage.If you need a ground (and you'll need one as you're up flying around), do a star-configuration at best possible physical implementation, so the currents to any on board device are it's own on that set of wire. The controller PCB is a good starting point, as it most likely has an effective internal ground plane and hopefully already prepared for this.A lowpassfilter works great as a noise barrier - the currents to the various onboard devices are low, so low losses in transferring useful energy, and great blocking of unwanted energy. The wires are thin, potentially saving weight. The filter might not, it comes down to how it is implemented (physical blocking - switchmode transfer - extra battery - )Oh,Get a working system, then start cutting away wires to optimize flight time.You'll know when you hit the limit, either in a good way or in an expensive one.. crash, please don't burn

author: TheDane
author_rank: Regular Contributor
timestamp: March 16, 2017, 01:00:40 am
content: Oh -Electrons influence each other, also through "thin air" - and also no air, for those still countingElectrons also love carbon, and carbon frames - so the ESC's can couple creating HF loops through the frame - no direct electrical connection required, only layer/isolator/layer/isolator/....sync prob.drive

author: W9GFO
author_rank: Regular Contributor
timestamp: March 16, 2017, 01:36:54 am
content: That doesn't look like much of a "power distribution board", it just has a large pad to solder all four leads of the ESCs to the same spot. Generally those pads will be "distributed" around the board.I would solder all the positive leads to one side and all the negative to the other. If you plan to solder the battery connector directly to the board then you should not have to worry about things falling off when soldering. If you intend to have leads soldered to the power input then it could be tricky soldering all four ESC leads plus the battery lead at the same time. I'll often use some thin strands of wire to tie things in place when faced with that kind of problem.The positive pad has an array of vias to connect to the bottom side of the board, the negative side does not seem to have them. Is there a large pad on the underside for all the negative ESC leads?

author: Yardstick
author_rank: Contributor
timestamp: March 16, 2017, 03:19:16 am
content: This will be an interesting one. I was considering some options for routing the larger power wires and in almost all cases I have some wires running close to and across the main FC board. It would be nice if the distribution pads were placed at the edges corresponding to motor locations -but then I wouldn't get to ask these questions!With all the talk of ground loops and other potential interference I'm wondering how they get away with it when using a regular PDB. Or maybe the same issues exist.W9GFO: Both the positive and negative pads have those vias. Both pads are also available on the other side of the board. I will run 12 AWG wires from the holes to a connector for the battery. It will not be connected to the pads directly. There's a big SMD resistor (with 0M50 printed on it) on the back of the board between the battery connection holes and the pad on the positive side. I haven't seen that before, so I'm not sure what it's about. For now I'm planning to solder two of the large leads to the pads on the back/bottom of the board and two to the top for each of the positive and negative pads. I was thinking about trying to hold down the first set of wires to be soldered on each pad with a tiny piece of wire looped through some of the vias. I'll have to make that decision or test it before I start doing anything.

author: james_s
author_rank: Super Contributor
timestamp: March 16, 2017, 04:48:12 am
content: You can have issues, but in my experience it's really not that critical. I've built several small multirotors and the only issues I ever had with electrical interference was when I tried using a FC with a compass on it, and some minor issues with noise in the video resolved by careful placement of the wires to the video transmitter and a filter.

author: rstofer
author_rank: Super Contributor
timestamp: March 16, 2017, 11:52:03 pm
content: Real airplanes vibrate a bit and have used bolts and nuts for, like, forever! Crimped terminals, of course. 25# minimum pull-out.Considering the current, I might use brass but zinc plated steel will work just as well. You could put one lead on the bottom of the board and the other on top with a bolt, a couple of flat washers, perhaps an external lock washer and a nut. If you really worry about vibration, add a jam nut. I can't imagine the weight of this assembly as being a determining factor on flight.

author: james_s
author_rank: Super Contributor
timestamp: March 16, 2017, 11:56:58 pm
content: I've seen a lot of multirotors and I've never seen anyone bolt on crimp connectors. High current gold plated bullet connectors are the standard for this sort of thing, or direct soldering. Every gram counts on these small craft.

author: Prehistoricman
author_rank: Regular Contributor
timestamp: March 17, 2017, 02:15:08 am
content: I'd tackle this by using a bunch of stands to hold every wire where you want it. That way you get all the routing you want and perfect solder joints on everything. If you don't have enough stands, then being as quick as you can with joints will probably do. Possibly even flowing a huge amount of solder on would add thermal mass to the board, therefore your other joints won't heat up as much.Remember you can attach wires to other wires! Make it messy!I can see using the holes to thread a wire through being very fiddly and then you heat it up and it all falls apart. Try it if nothing else works.

author: Lovely_Santa
author_rank: Contributor
timestamp: March 17, 2017, 09:35:00 am
content: Hi, Some years ago i made a quadcopter as my 'thesis' for middle schoolWe used a little PCB (weight 10 grams) as PDB... attached a picture of it (sory for bad quality)In the 2nd picture you see it's mounted underneath the actual Flight Controller. The wires of it will connect directly to the battery, and then you have 8 +/- wires, we used 4 for the ESC's, 1 to power the FC, 2 for LED strips and the last one to check the battery power (fail safe). It looked realy nice and we had no spiderweb of cables running all over the place. With the extra board and removing acces leads we actualy lose some weight on itHope this gives you an other point of view.Kind regards,Lovely Santa

author: Yardstick
author_rank: Contributor
timestamp: March 27, 2017, 03:56:53 am
content: I thought you guys might enjoy a few pictures of the semi-finished product. I did successfully thread some wire through the board to hold the bottom wires on, but I'm pretty sure that was not necessary. Thank you all for the ideas and words of encouragement!I think you'll appreciate the opened up image first.It was built up with low profile as a priority (no real reason, just because I could really)And in nearly complete form: