Most teams’ electrical panels look less like panels and more like spaghetti attached to the frame of the robot. An ugly electrical layout is almost always the result of poor planning, or no planning at all when it comes to component placement and wire routing. Here are some tips on how to plan your electrical layout.
In the introduction to my electrical series, I mentioned three classifications for FRC electrical layouts: the ugly, the pretty, and the effective. (not as catchy as I hoped it would be) Of the three, the most common is the ugly. Most teams’ electrical panels look less like panels and more like spaghetti attached to the frame of the robot. An ugly electrical layout is almost always the result of poor planning, or no planning at all when it comes to component placement and wire routing. Most teams will stick to their ugly wiring season after season, but if the electrical system is planned out just like the rest of the robot, the electrical layout will come out more robust and aesthetically pleasing, with no loss of time or money during build season. The methods I lay out below are some of the essential concepts that I, and my team, have adopted to improve our electrical system.
Know your constraints
Like any other part of the robot design, knowing your constraints is essential to making an effective electrical system. However, unlike mechanical, where your constraints are defined primarily in the game manual, electrical design constraints are defined both in the manual and by the robot itself. Knowing exactly where on the robot electrical components will fit before putting it all together will ensure that the electrical system does not interfere with mechanical parts. Without examining the robot design closely, it’s easy to place components in areas where they will interfere with mechanisms, or where they will be difficult to access when they need to be replaced. Rules on component placement must also be kept in mind when designing the electrical system. Having the router and breaker easily visible is easy to do, especially when compared to how easy it will be to fix a violation like this at competition. Small mistakes, like poor breaker placement or putting motor controllers in a hard-to-see area, can cause huge headaches at competition; but, by understanding your constraints, problems like this are easily avoidable.
Use CAD to design your electrical system
If your team is like almost any successful FRC team, you probably lay out the vast majority of the robot in CAD before making it a reality. Designing the robot in this way is necessary to make sure all the mechanisms fit on the robot, and do not interfere with each other. However, few teams ever design the electrical system as part of the CAD. To this, I can only ask “why?” Like any other mechanism, the electrical system takes up a large amount of space and it is vital to the performance of the robot. So, why wouldn’t you give the electrical system with the same amount of precision and care that is given to other essential parts of the robot? Electrical CAD will allow you to plan the placement of every part, and determine how long every wire needs to be before putting them in the robot. This ensures that the entire system meets design constraints while serving all of its functional purposes effectively.
Think about why your team doesn’t CAD electrical. Below are some of your most likely answers:
“We don’t have CAD models of electrical parts, and they would take forever to make.” All you have to do is google “FRC [part name] CAD” and, 99% of the time, the part you want will show up. Keep all your electrical component files in one place, and save them from season to season; having a large library of components available to you will mean you don’t have to scour the internet for those parts again.
“Finding parts, laying them out, then harnessing them is very time consuming.” Have multiple students work on electrical CAD at the same time as the robot CAD is being created. Specific people are always CADing out smaller parts. For example, if you have three separate panels, have three students design one panel each, giving them each a list of specific components that need to be on their panel. By designing the electrical system in this way, my team has actually saved some time during build season because the entire system can be finished before there’s even a robot to mount it to.
“it’s too hard!” I’ll admit, the Autodesk Wire Harness Environment is rather confusing if you haven’t ever seen it before, and mastering it is even more difficult. However, there are a variety of tutorials online, including the Inventor help documentation, specifically designed to teach you how to use it. It’s a lot like learning any other new piece of software. It may look completely alien at first, but once you know the basic concepts, it’s a breeze.
There certainly is a steep learning curve to electrical CAD, but integrating it into your team’s build season can happen quickly and easily. Much like any other skill, it will be passed down from older students to new students, and it will simply become a part of your team’s culture.
Recording an idea is important, but making the idea accessible will allow it to be iterated upon, and referred to when new ideas are formed. Just as you record your electrical design in CAD, you should produce documentation, and document the reasons why certain design decisions were made.
Thankfully, Inventor (and any other CAD software, I’m sure) makes the first two jobs quite easy. Simply put the electrical panel assembly into a drawing sheet, throw in dimensions and annotations where needed, and print it out. Inventor also has a handy tool that spits out an XML file (other programs may do it differently) with definitions for each wire in your system, where it connects to, how long it is, and what harnesses it passes through. Simply import this file into Excel, delete the columns you don’t need, pretty it up with some headers, and print it out. Once these specifications have been created, include a small amount of documentation, created by the designers of the system, outlining why certain design decisions were made. These “why” statements should mostly cover component placement, but other topics, including harness locations, could be useful to to cover.
These papers, known on my team as the electrical “spec sheets,” ensure that the electrical system will be constructed just as it was in CAD. Adhering to these sheets means that you will know what the system should look like when it’s done, and that no wire runs interfere with robot mechanisms. The former means that the electrical system may be aesthetically pleasing and durable. However, the latter is extremely important, and the reason why my team started making these spec sheets. In 2014, we followed the electrical CAD to a T, except for one 24V photosensor with a built-in cable that was too short to go the way the CAD specified. Instead of extending the cable to adhere to specifications, it was just connected in the shortest route possible. Eventually, it was cut in half by our catapult, shorting out the 24V line in the power distribution board, forcing us to replace the sensor and the PDB. Producing documentation on the electrical system will encourage students to adhere to specifications, making massive failures like this less likely. Using these essential concepts when designing the electrical system ensures that it will be easy to repair, less prone to failure, and more aesthetically pleasing.