Start as you mean to go on -- The Coptermatic Chronicle Part 1

Minor background before I start.  

I've been playing with wheeled robots for a while, using the Basic Stamp as a controller.   Just tinkering, and more interested in the software side of things (as well as having something that annoys the cat).  My enthusiasm died out about 7 years ago, then my son gave me a Lego Mindstorms NXT kit for Christmas, and I was off and running again. 

At about the same time, a co-worker got me started on radio controlled helicopters (Blade CP/2 to start with, moving up to Blade 400 and TREX-450 over the last few years).  You can't have too many expensive hobbies :)

Managed to do quite well at this helicopter hovering in the back yard, and was doing quite well until about a year ago when I flew my pride and joy into a tree and broke just about everything except the tree.


"I wonder," I wondered, "if it would be possible to combine my robotic hobby with my RC flying hobby?" 

Poked around teh intarwebs a bit, and ended up here looking at the APM and the Arducopter code. 

Thus started work on what I am now calling Coptermatic, the Automatic Helicopter.  (with apologies to Wallace & Gromit)


So off we go:

Got my workbench set up, got me new Weller soldering station set up, played with some Arduino programming for a practice, and decided that tonight was the night.  


I solder all the pins on the APM. I solder all 48 pins on the right angle servo connector (the three pin monstrosity on the end of the board).  I've got all the pins on the APM,  

But the servo connectors seem a bit fragile, and my attempts to test-connect a couple of servos and Rx connectors seems wonky.    Imagine my amusement when I discover that I've soldered the damned servo connector on backwards.  For that connector ONLY, the black plastic bit doesn't go flush with the top of the board.  What's worse, I compared what I was doing with the pretty picture in the instructions four or five times and didn't notice my error. 


OK, so now I am sort of stuck.   I'm an amateur with the soldering iron (more of a software engineer with a  predilection for tinkering).  I'm not at all sure how to unsolder 48 connections; I think I need something more than desoldering braid and bad language. 


The current plan (as blessed by my long-suffering and patient wife) is to use this APM as the brains for a small wheeled robot which I shall call the Pipbot (in honour of the Fallout series of games) and to buy another APM from DIY Drones for the 'copter. 


So a bit of a (not-so) cheap lesson in following instructions.  This hardware stuff is a lot less forgiving than software.


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3D Robotics
Comment by Chris Anderson on April 29, 2011 at 10:45pm

Ugh. Sorry to hear that. The best way to unsolder is to just cut off all the pins with a snipper and unsolder them one at a time. Use a solder braid or vacuum desolder to get the solder out of the holes.


Got a picture of the mistake, so others can learn from this episode?

Comment by Wanabigaplane on April 29, 2011 at 11:03pm
Backwards?  A clarification is needed. If the pins point towards the centre of the board, then yes, you only have to slide off the plastic bit, and unsolder the pins one by one. However, if the pins point away from the centre of the board, you can compensate for the error by installing the servo connectors upside down.  Jack.
Comment by Nigel Conliffe on April 29, 2011 at 11:23pm
This is what it looks like. Compare this with the picture on the assembly instructions. The black plastic thingie should not be against the pcb, but should be in the air.

This means that the remaining connectors are not long enough for the servo plugs to make a good connection.
Comment by ARHEXA on April 30, 2011 at 12:30am

looks bad,

you can't even push the pins more because of the plastic...

have you tried to connect the IMU board ? please post a picture,

maybe it's not too high after all.

you should put some thick transparency or plastic sheet above the highest header row to prevent it to touch the bottom of the IMU board...

Comment by Wanabigaplane on April 30, 2011 at 12:32am

I see. No problem. To me, removing the pins by one would be the easiest route, but you would have to wait for another connector. When I received my APM, I  did not realise I had thrown the  connector with the packing until I started the assembly. Cutting up servo extender cables and soldering the wires directly into the holes where the connector was meant to go turned out to be just as good as the real thing.

Now, if you don't want to unsolder the connectors, and you are prepared to figure out the purpose of the individual pins, you have another way out. Look at the line of outpointing pins closest to the board. They are all connected to ground. Look at the next row. They are all connected to positive.

Now consider the top row. Each pin is connected to servo signal input or an output, and they are long enough to slide on one your servo connectors crosswise. Your receiver is arranged exactly the same way. You could use one servo lead to access the signal line for three servos at a time at the radio output, the APM input, and the APM output.  Just consider your servo leads as a means of connecting onto the pins in the receiver and the APM, and forget about assigning each lead to its particular servo.   A few cm away from the APM cut all the leads, and re-assign them to their correct destination. Use servo extenders for connecting the servos to the APM - don't cut the servo leads themselves!

Lastly, the positive and negative from the receiver will have to be soldered to the APM, and to the positive and negative for each servo.

Hope this helps. Unfortunately, the details are up to you, and of course I take no responsibility if you stuff it up! Jack.




Comment by ARHEXA on April 30, 2011 at 12:44am


i like the idea of using the signal pins only.

the question is - does the IMU board sits correctly on there ? or the headers are too high pushing it ?


unsoldering the pins sould be doable.

just use the soldering iron to heat the pins on the solder side, once the solder point is melting, push it down, it should slip out, melting the plastic connector a bit to allow it loosing out.

don't forget to start from the highest (inner) row, and try to work on a pin on each side of the PCB altering, to allow the pcb environment to cool down a bit...

Comment by Nigel Conliffe on April 30, 2011 at 12:51am

Thanks, Jack.

That's an interesting idea -- running a separate power bus for the servos and just using the signal connections on the pre-stuffed socket strip.  That, or cutting off the 3-deep socket strip and wiring up a set of pig-tails for the servos.  I shall not blame you if it leads me astray :)


And @AR..  the IMU clears the pins on the 3-pin socket-strip, so we could be on to something here.  I'll play some in the morning (it's about 1:00am here in Seattle)
Comment by ARHEXA on April 30, 2011 at 12:56am

when i think of it - you can use nippers to pull each pin out while you heat the solder on the other side.


it might be some work now, but will allow you a much cleaner and not messy environment in the future..

splitting servo extension wires to power and signal wouldn't take 5 seconds neither...


these 3 row headers are a common type and you should find it locally on pro's electronics stores...

3D Robotics
Comment by Chris Anderson on April 30, 2011 at 7:07am
I've taken the liberty of modifying your photo and adding it to the top of the original post, to conform with our posting guidelines (image/video should lead every post)
Comment by Bertrand Duchiron on April 30, 2011 at 8:06am
It happen to me with my 3th APM, I was wondering why the soldring of this headers was more difficult than the 2 first until I realize I put the headers on the wrong side. I try to desolder the pins after cuting them but it seem that I apply to much heat on the board and the copper layer delaminate, the board end in the trash bin and I brought another one. I learn from my mistake.


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