• aditya mehrotra.

chip updates: let's fix some wiring, and add some copper shielding [updates]

Todayyyy is the day the copper shielding shows up - and we're going to be ready for it when it does so it can just go on. At the moment, there are a few problems with wiring when we open the the center of CHIP and I want to fix those before we add the shielding so we don't need to fix them later.

Problems to Fix:

(1) The tape used to hold on the sparkmaxs and other components is coming off - ee want to replace that with true VHB tape.

(2) The wiring is a loose rats nest, we need to turn it from chaos into controlled chaos.

(3) The Jetson mounting and IMU mounting need fixing after the shielding and the wiring get fixed.

So let's get to it, starting with number one.

problem one: fixing the mounting of solid components (sparkmax and can bus)

So initially, here, we were going to un-mount all SparkMAXs and basically re-stick them to the wooden frame. But we realized for the controllers this wasn't worth it because most of them were pretty stuck, there are only two that aren't stuck and those are on a part of the wood nothing will stick to because of a dumb set of bumps on the wood. We can't take the whole wood off to file that down and fix it, but the controllers are constrained enough where this shouldn't be a problem. We'll fix it for the next version.

The RoboRIO, however, we took off all the duct-tape and mounted that with a single strip of VHB tape like we were originally planning to do.

problem two: fixing the rats nest of wiring between components on-board

Here's the before picture of the problem. The wires were everywhere, there were no zip-ties or anything. I mean I want everything I make to be well-designed and beautiful, however this is a prototype and my time is better spent making it work than making it pretty. Even still, I think I should make an attempt to make it look at least organized.

Now here's the after. It's not much different than the last time. But here what we did is first, get rid of the duct-tape around the edges holding on the CAN BUS wires, and we secured the CAN Pin Connectors with VHB tape to the frame. Then we bundles the CAN wires and zip-tied them together. Then we went through the rest of the wiring step-by-step to see if there were any last issues that needed fixing before we seal this compartment up later, and then we zip-tied things to each other.

Using some foresight, when we seal this compartment up we won't have access to things like the sparkmax USB ports and etc, so one thing we did was leave an orange USB cable to at least one of the sparkmaxs so we would be able to update them if needed.

All wires are either zip tied to each other, the frame, or VHBd to the frame.

problem two-point-five: fixing wire strain

Okay so now the problem of wire "strain" and what I mean by this, is you've likely noticed there's a trend with encoder wiring becoming an issue. Those wires somehow need constant replacement. This is likely because, first, the REV robotics crimps and our crimps on the NEO encoder wires are actually really bad - so now all 12 motors encoder wires have been replaced with the DigiKey soldered versions.

But also, the reason is because they were kinda being strained by the rest of the cable to the motor and how that whole thing was packaged, those cables were never zip-tied down and since the encoder cable was always shorter than the power lines to the motor, the encoder cable was holding a lot of weight which caused them to be constantly ripped out. We want to increase the slack in the encoder cables so what we did was fix the whole motor cable to the frame. We zip-tied it.

You see the slack that now exists on the blue encoder cable? Before it was being pulled to the side, literally, by the weight of the rest of the long motor cables. This was really only an issue for the knee and hinge joints, so we fixed it on all four legs.

addition one: adding the copper faraday cage

Now, the exciting thing arrived! The copper faraday cage/EMF blocking fabric. So it's time to mount it! We will mount copper EMF blocking fabric around the entire, what we're calling, "power-core"of the robot that houses all the power electronics and the power distribution. The point of the fabric is to block any EMI radiation from the motors and power systems to the GPS and compass and IMU as well as other sensors.

Here's the fabric, it came in a 1'x4' roll. We're going to use exactly all of it. And we're going to simply cut it with a scissor, and stick it with VBH tape. This is going to (a) look great, and (b) serve a really proper purpose.

I'm not going to go through every step, it isn't worth it. But basically what we did is measured the gap we wanted to bridge and added 1cm to each side so we gave the fabric enough space to crinkle around wires and bumps. We added slits in the fabric for anything that had to poke through like wires or metal supports.

We did this to the top side, under the IMU, the bottom side, the left and right sides of the power core:

We did also notice, that the GPS/Compass, which would be the most affected by any magnetic interference due to its reliance on detecting the Earth's Magnetic Field, would need the most protection and there was something still, even after all of this that could disturb it.

Yep, there's a motor right in front of the GPS system and many power wires running underneath it. By this point, I had exactly 1'x1' of the cloth remaining. So I decided to spend the rest of the cloth, wrapping the front-left shoulder motor.

And voila, here is the finished product. A very pretty copper colored CHIP but for a reason! Not just for decoration, but to build a more robust system where the sensors are not bothered by EMI and such. The copper cloth needs to be grounded to be effective. This is an issue we will deal with later, however, I think grounding it to the frame which touches the ground when the robot sits is sufficient. We just need to be careful not to get shocked around the fabric, there's a lot of radiation this cloth is going to try to re-direct. Hopefully it doesn't all turn into static energy. If grounding really becomes a problem, we can connect the cloth electrically to the feet of the robot.

And that's how we make a mess look pretty, and also shield our electronics from harmful radiation!

#copper_shield #pretty_colors #electronics #physics #omgrobots #waow

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