pic: A little teaser from 3571

[JustPlyZ]

loading photo ...

[Lil' Lavery]

That's a very aggressively spaced electronics board. So much so that I have to question why it had to be so compact. That wire routing is certainly beneath the minimum bend radius of 12 AWG wire.

[icq10]

Looks quite nice, but I am always concerned that some of the thicker wires are breaking due to too much bending. We had one robot of the last years that we are about to revive for a fundraising event and it had connecting issues... Took us 3 days to figure out that it was one of the networking cable that was broken due to too much bending with cable ties.

But at least this is a nice overview, the wiring cleanup is always a big challenge!

[Jared Russell]

Looks good to me.

[Briansmithtown]

How water resistant is it? We need to know this for... future endeavors.

[Addison4300]

I love the organization, So very perfect! That is also an excessive amount of Talons

[JustPlyZ]

Originally Posted by Addison4300

I love the organization, So very perfect! That is also an excessive amount of Talons

If you can guess the amount of cims we're using and what type of drive we are using, I will send you a button.

[TheThings]

Can anyone say interference? Also, look to the fact that the roborio isn't supposed to be near things that are that powerful. Your talons also are going to get hot. Just a warning from our electrical lead.

[Alan Anderson]

Originally Posted by TheThings

Can anyone say interference? Also, look to the fact that the roborio isn't supposed to be near things that are that powerful.

Can you clarify what you mean by that?

[TheThings]

(this is the Electrical lead): By running the pwm signal wires next to large motor wires that could potentially have upwards of 40 amps through them, you risk electromagnetic interference across the pwm. For this reason we like to run our pwm cables as far away from our power cables as possible, and where they have to come near each other, we cross them at a 90 degree angle. This prevents the magnetic fields on the power cables from interfering with pwm communication.

[Foster]

Oh how much I want to covet this board, hold it, whisper things to it. But sadly there isn't a single label on any of the cables or talons. So sad, a thing of beauty, struck down by such a minor thing like being able to trace wires.

[Caleb Sykes]

Originally Posted by TheThings

(this is the Electrical lead): By running the pwm signal wires next to large motor wires that could potentially have upwards of 40 amps through them, you risk electromagnetic interference across the pwm. For this reason we like to run our pwm cables as far away from our power cables as possible, and where they have to come near each other, we cross them at a 90 degree angle. This prevents the magnetic fields on the power cables from interfering with pwm communication.

Anecdote: I have never had a problem when routing PWM wires and power wires together.

Physics Note: Even if the magnetic field were substantial, routing PWM wires parallel to power wires should not have an appreciable effect on signal, since the magnetic field would only cause a Hall Effect on the signal wires. That is, the magnetic field would not speed up or slow down the electrons, it would just shift the electrons to one side of the wire or the other.

Just for fun though, let's calculate the magnetic field created by a 12AWG wire, and see how that magnetic field affects a 22AWG PWM cable next to the power cable.

Take:
I1 = current in the 12AWG wire
I2 = current in the 22AWG wire
r1 = radius of 12AWG wire = 1.03mm
r2 = radius of 22AWG wire = .32mm
d = distance from center of 12AWG to center of 22AWG wire

The magnetic field B(r) created by the 12AWG wire at a distance r (r>r2) from the center of the wire will be:
B(r) = (mu0)*I1/(2*pi*r)

The magnetic field will be perpendicular to the propagation of the electrons, which means the magnetic field will cause the electrons in the 22AWG wire to move either toward or away from the 12AWG wire (This is the Hall Effect). The difference in voltage VH between the near side and the far side of the 22AWG wire will be given as*:
VH ~= I2*B(r)/(n*t*e-)

Where B(r) is given by the first equation, n is the number density of charge carriers of conducting material, t is the thickness of the 22AWG PWM cable, and e- is the fundamental unit of charge.

Combining these equations, and taking mu0 = 4*pi*10^-7 (mks), n=8.49*10^28 m^-3 (copper), t = r2 = .00032m, and e- = 6.02*10^-19 C, gives:
VH = (4.6*10^-14*I2*I1/d (mks)) V

Plugging in some ridiculously high values for I1 and I2, and a ridiculously low value for d:
I1 = 1000A
I2 = 10A
d= .1mm

This yields a potential difference between the near and far side of the PWM cable to be 5*10^-6 V. Which could be measurable if you had a good sensor, but doesn't come anywhere near the 5V** high voltage transmitted by the PWM cable.

Please don't route your signal and power wires separately for this reason.


*At these small of distances, the magnetic field can not be assumed to be constant over the entire width of the cable, hence the ~ sign.
**Source needed

[arichman1257]

Originally Posted by JustPlyZ

If you can guess the amount of cims we're using and what type of drive we are using, I will send you a button.

6 cims. Swerve drive.

[philso]

Originally Posted by TheThings

(this is the Electrical lead): By running the pwm signal wires next to large motor wires that could potentially have upwards of 40 amps through them, you risk electromagnetic interference across the pwm. For this reason we like to run our pwm cables as far away from our power cables as possible, and where they have to come near each other, we cross them at a 90 degree angle. This prevents the magnetic fields on the power cables from interfering with pwm communication.

^
|
|
This is standard practice in industry and is described very thoroughly in literature on Electromagnetic Interference.

Originally Posted by Caleb Sykes

Anecdote: I have never had a problem when routing PWM wires and power wires together.

The PWM signals are "digital" and have a large noise margin, by design, and their response to noise is non-linear. Increasing the amount of noise induced on your PWM wires will not cause noticeable degradation in performance until you have used up all of your noise margin. Shifting your wires around may change the coupling enough to start causing a problem. Been there, done that, had to write reports about it, didn't get a T-shirt for it.

Originally Posted by Caleb Sykes

Physics Note: Even if the magnetic field were substantial, routing PWM wires parallel to power wires should not have an appreciable effect on signal, since the magnetic field would only cause a Hall Effect on the signal wires. That is, the magnetic field would not speed up or slow down the electrons, it would just shift the electrons to one side of the wire or the other.

A current in a wire WILL induce a current in a wire that is parallel to it. That is why it is standard practice in industry to avoid running power wiring and signal wiring together, in the same bundle. Please DO route your signal and power wires separately for this reason.

You are correct in thinking that the Hall Effect is insignificant in situations like this. I have never seen any mention of it in any literature on Electromagnetic Interference or in any of the many courses my employers have paid to have me attended on the subject.

[Caleb Sykes]

Originally Posted by philso

^
|
|
This is standard practice in industry and is described very thoroughly in literature on Electromagnetic Interference.




The PWM signals are "digital" and have a large noise margin, by design, and their response to noise is non-linear. Increasing the amount of noise induced on your PWM wires will not cause noticeable degradation in performance until you have used up all of your noise margin. Shifting your wires around may change the coupling enough to start causing a problem. Been there, done that, had to write reports about it, didn't get a T-shirt for it.




A current in a wire WILL induce a current in a wire that is parallel to it. That is why it is standard practice in industry to avoid running power wiring and signal wiring together, in the same bundle. Please DO route your signal and power wires separately for this reason.

You are correct in thinking that the Hall Effect is insignificant in situations like this. I have never seen any mention of it in any literature on Electromagnetic Interference or in any of the many courses my employers have paid to have me attended on the subject.

I'm really having trouble understanding how there would be any appreciable electromagnetic interference caused by a single wire with a constant (or at least, low frequency) current running through it. This situation would only cause a slight magnetic field around the wire, and should not be creating any electromagnetic waves. The situation would clearly be different if the current was AC, but we are not dealing with AC currents here.

It is quite possible I am in this way over my head and that I really don't understand what is going on. Could you possibly link to a more detailed description of this interference you are describing? Everything I am finding in searching relates to AC circuits.