FRC Electrical- Form Versus Function

The one aspect of robot design I see overlooked the most often is electrical. Most of the time, electrical boards are done haphazardly in the last couple days of build, and end up messy and extremely difficult to repair. When your electrical inevitably has a failure at some point in the season, you’ll discover it’s rather hard to find one specific piece of spaghetti and put it in one specific place without disturbing all the other spaghetti in your robot.

I’ve seen otherwise excellent teams miss matches because they couldn’t figure out what failed among their heap of wires. When you do electrical right the first time, the rewards are enormous. My freshman year, I joined a 3-person electrical team in a ~40 student program. We were rushed to wire the entire robot in the 3 days before bag and tag. Like most teams in that situation (and by that I mean 75% of FRC teams) our electrical came out messy and inefficient. I recall spending nearly half an hour trying to plug in a PWM cable between matches at champs. These are the kind of struggles I watch many teams encounter throughout their competitions, even though the majority of these problems are preventable, and would be easy to fix if not for an inefficient electrical design. Thinking out the electrical system before building it has an enormous positive effect on the performance of a robot. When electrical is done properly, it is less likely to fail, regardless of what kind of bashing it takes. In my series of posts about electrical, my goal will be to share some of the lessons I have learned in making a reliable electrical system.

This is an example of a pretty typical FRC electrical layout. Imagine trying to replace one of those motor controllers that’s pinned in by the robot frame.

The most common problem in FRC electrical is incorrect wire lengths. In this example, zipties are used to hold groups of wires, in an effort to keep everything together. However, if you look more closely, it’s easy to see that these zipties are also holding together large bundles of excess wire. It’s common practice to do this, but it can have a serious impact on the performance of your electrical system. Excess wire clutters the electrical panel, making it difficult to make even the simplest fixes, including replacing motor controllers and repairing damaged connections. Those bundles will act like little walls, obstructing your view of other wires and making it difficult to do more precise repairs. Not only do wire bundles cause repair headaches, they can reduce the performance of the robot. Excessively long wire results in line resistance between components, and makes signal lines more prone to picking up electrical noise. As a result, sensitive analog components will not be able to perform as well.

Another problem I often see in FRC electrical is poor component placement. Although this image doesn’t show any severe problems of the sort, I’ll use the placement of the sidecar as an example. I speak from experience when I say that trying to fix something that you can’t see is a nightmare. Try to keep major “hub” components (those with many connections or connections that may need adjustment regularly) easily visible and exposed. By doing this, it’ll be more likely that your repairs will be in an easily accessible location. At this point I’d like to put to rest an unnecessary fear of many electrical freaks like me- having motors near analog, or other sensitive signals usually will not result in interference problems. EMF interference by motors, particularly CIMs, will mostly occur in the FM band, much higher than anything that would cause detrimental interference problems.

This is a huge step forward from the last example.  However, it breaks the FRC paradigm of “function over form.”

 

Before I say anything someone is going to yell at me about, I’d like to point out that I’d take this layout over the last example in a heartbeat. However, this image provides a rare example of overzealous wire lengthing and sleeving. Personally, I love wire sleeve. It’s an easy way to hide away ugly PWM runs and it can protect wires against damage from mechanisms. Getting overzealous with your sleeving and wire shortening, though, can cause horrible difficulty when trying to repair your electrical board. For example, imagine if one of those motor controllers overheated (since its fan is upside down), and now you have to replace it. These wires are extremely short, and won’t allow for any leeway when detaching the fried part. A little bit of tolerance in your wires will allow you to put in and take out parts very easily, without sacrificing quality or aesthetic. In a debugging situation, tubing will make it more difficult to trace the path of a wire. Removing a wire from the robot is essentially impossible in this example, as it will get stuck on the large zipties holding the tube, and pulling the wire straight through the tube may cause it to get caught on other wires, potentially damaging them or pulling them out of position.

A very small portion of teams take the appearance of their electrical very seriously, and make an extremely pretty layout with lots of sleeving, through-frame wiring, and 20 pounds of zipties. Yet, what I’ve found is that this approach can result in struggles on the field. In order to have a successful robot, the electrical system must be build robustly. What really matters when making your electrical boards is that they will not fail in a match. All the sleeving in the world won’t prevent a cable from falling out of its port.

Not as pretty, is it?

Although the above example is clearly unfinished, it provides an excellent example of an electrical layout that is clean, and would be easy to repair. Notice how all the power wires are neatly lengthed and routed in an organized manner, but they have enough slack that parts would be easy to take out or move. Sure, it isn’t all perfect 90 degree angles, but the layout is clean and highly functional. Ultimately, the electrical system should take on the “function over form” concept. In order to have a successful electrical system, it must be designed with reliability and functionality as the first priority. In no way is this a “perfect” example of an electrical system, but it shows my point that the prettiest electrical isn’t always the most effective, or the easiest to fix.
For most teams, electrical is either over thought, or it is an afterthought. Designing a safe, reliable, and efficient electrical system can be very challenging if you overthink it- the end goal of the robot (usually) isn’t to be pretty, it’s to be effective. Electrical should be designed with the same priorities in mind- making sure the design is functional and efficient over its aesthetic appeal. In my series on FRC electrical design, I hope to share my ideas and experiences in making a highly effective electrical system.

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