Electrical types: help!!!!!!

[Monkeyleg]

I have spent at least eight hours over the last several days searching and calling for the simplest thing: a short length of stranded 18 AWG center conductor coax cable. What I need to replace is four 1.25" lengths of 18 AWG stranded tinned copper center conductor, plastic dialectric (sp?), tinned braided copper shield, and poly sheath. Current OD is .15".

What I'm finding are 1000 foot rolls of anything close, or cable with OD's of .405 or more. This is going in a tight spot, so that's too much.

I ordered what sounded like exactly what I needed from a place in CA, but got dual wire center conductor. I called and told him he sent the wrong cable, he complained about losing money on postage, then send me 23 AWG center conductor.

The cable was in my drone, so it must exist somewhere.

Any suggestions very much appreciated.

[Brad Johnson]

Sounds a lot like plain old Belden shielded audio cable. Got a pic?

Brad

[Monkeyleg]

Sounds a lot like plain old Belden shielded audio cable. Got a pic?

Brad

I called Belden. The closest they have is 19 gauge .405", and nobody has it in less than 500 foot rolls.

It's the stranded center conductor that makes it difficult. I think the mfr used stranded because it would adhere better to the small pad on the circuit board. Or maybe it's all the Chinese had  that year.

It doesn't make sense to me to have shielding on the power wires to the motors for just an inch or so, and then have unshielded wires elsewhere, but someone who knows more than me said the shielding on those cables at those spots keeps from interrupting the GPS reception.

[dogmush]

I won't be at work until monday, but when I get there I can poke around our pile 'o coax and take a look. But that's pretty small for us to have.

That sounds like RG-180.

http://www.pasternack.com/flexible-0.145-rg180-95-ohm-twinax-cable-fep-jacket-rg180b-u-p.aspx

http://www.awcwire.com/productspec.aspx?id=m17/95-rg180-coaxial-cable

[230RN]

Why do you feel  you need those exact specs?

Could you have just "commoned" the conductors in the two-conductor coax?

Could you just slip some solder wicking over some 18ga stranded insulated hookup wire for a short run? I've done that, and just slipped some spaghetti over it all.

I've also just put a loop in the ends of solid conductors for better soldering to the circuit board. IOW, you don't have to splay out a stranded conductor to make good firm contact.

Do you really need the flexibility of stranded wire in the first place because of component movement?

Could you just twist any two conductors together to make a half-assed "twisted pair" "shielding?"

Do you really need the shielding to be tinned?

Most of that kind of stuff at audio and moderate power levels just ain't all that critical.  I repeat: "most."

19 gauge? Hm.

Frankly, I fail to see why this is such a problem, let alone an eight-hour one.

Terry

REF:
http://www.jestineyong.com/wp-content/uploads/2007/08/solderwick.jpg

[cordex]

ML,

I put in a request with one of my clients. I will let you know what they say.

[Monkeyleg]

Why do you feel  you need those exact specs?

Could you have just "commoned" the conductors in the two-conductor coax?

Could you just slip some solder wicking over some 18ga stranded insulated hookup wire for a short run? I've done that, and just slipped some spaghetti over it all.

I've also just put a loop in the ends of solid conductors for better soldering to the circuit board. IOW, you don't have to splay out a stranded conductor to make good firm contact.

Do you really need the flexibility of stranded wire in the first place because of component movement?

Could you just twist any two conductors together to make a half-assed "twisted pair" "shielding?"

Do you really need the shielding to be tinned?

Most of that kind of stuff at audio and moderate power levels just ain't all that critical.  I repeat: "most."

19 gauge? Hm.

Frankly, I fail to see why this is such a problem, let alone an eight-hour one.

Terry

REF:
http://www.jestineyong.com/wp-content/uploads/2007/08/solderwick.jpg


230RN, each of these little lengths of coax transmits the power for the motors, to the Electronic Speed Control board, and then to the motors themselves. If anything screws up--solder joint comes loose, wire melts, whatever--the motor stops and the quad copter falls out of the sky. And then the user is out the $800 to $1300 he paid for it.

The manufacturer used stranded center conductor, I suspect because it's more flexible than solid, and there's a lot of vibration and a bit of twisting going on. The maximum continuous current for the motor is 14 amps, with a no-load current of .45 amps, so if the quad copter is being driven hard, even the 18 gauge is getting to the point of being a fuse ribbon.

[230RN]

OK, understood, especially with respect to: "Do you really need the flexibility of stranded wire in the first place because of component movement?"

And yeah, 14 amps is pushing it.

The next question is "Why did they fail or need replacing, and can you do something with your "new" wiring to avoid that problem in the future?

Not to be snarky, but it really helps to know the exact applications to find solutions to the problems we encounter on this board.

Like:

"I need to conduct 50 A.  Will automotive starting cable do it?

Then, two or five posts later, you find out it's from a household fuse box to an appliance.  

Answer: no.

Or, two or five posts later, you find it's to run a 200W linear amp under the dashboard, excited by the guy's 2-meter handheld rig.  

Answer: yes.

Hyperbolic hypothetical situations, but the point is made.

Terry.... just feeling feisty this morning, 230RN

[Monkeyleg]

Terry, the original motor wire (from ESC board to motor) was two strands not much thicker than human hairs. They frequently melted under load, and the copters would just fall out of the sky. The manufacturer denied the problem, but did replace the wiring under warranty (tough luck if you bought it used), but only after a crash.

The ESC boards were also made too light for the new model of motors, which have a much higher current draw than the previous motors. The MOFSET boards would burn up, and the copters would fall out of the sky. The manufacturer denied the problem, but issued upgraded boards under warranty, but only after a crash.

I believe I've finally found the cable, though. Canare GS-6 18 AWG stranded copper center, braided copper shield, .225" OD (a bit thicker than the OEM cable). I found it at showmecables.com

If it doesn't look like a garden hose or a human hair when I get it, I'll be a happy guy.

[230RN]

OK, I didn't notice the remark about it being in a drone in your OP.  I guess I didn't have my drone glasses on when I read it.

Pardon the bluntitudinality in my post, but something more or less frustrating had just happened.

[Brad Johnson]

Why the fancy cable if it's just carrying power and not signal? Seems to me some simple lamp cord would work.

Brad

[dogmush]

Why the fancy cable if it's just carrying power and not signal? Seems to me some simple lamp cord would work.

Brad

They are shielding the on-board receivers from the motor power. kinda standard on small electronic stuff.