Space for electrical
 

So my rookie team is trying to make our robot really small so it can balance on the bridge with two other robots. I'm incharge of electrical dept and they want the electrical layout to take up as little space as possible. we are usuing 2 jag speed controlers (we might switch to victor if we have $) 4 drivers 6 wheels and all the basic stuff (pd board battery router crio) has to fit on the chasis too. what do you guys think is the least amount of space we could use? right now we are aiming at around 28 x 28 but we might be able to get it smaller

Re: Space for electrical
 

Area, or volume? There is no restriction on how tall your electronics board is, or how many decks it has, aside from all the lights needing to be visible. Or even orientation--teams have done vertical boards in the past.

You say "4 drivers". What do you mean by that? If you're trying to say 4 drive motors, you need to add two Jaguars or Victors.

Re: Space for electrical
 

wait, you need a speed controller for each motor? and thanks the vertical idea is really helpful, ill look into it. but the mentor on my team said the battery crio and pd board all have to be easily accessible so we couldnt deck anything on top of it, and we cant deck it on top of anythign else cause its the heaviest and takes up most of the space anyways.

Re: Space for electrical
 

How small you can make it depends on how creative you get. Keep in mind that you can mount some of these components sideways or upside down, so the space requirements are really three-dimensional not two. I'm going to go through some of the design considerations with you now, but I realize this is a lot of information at once.

I'd recommend leaving the cRIO right side up, as well as the power distribution board. Make sure you leave enough space in your design to plug in all the connectors, and leave at least 1" (Correction: that should be 2" :o ) of empty air over the Jaguar or Victor fans to allow room for airflow. It's good to be able to see all of the various indicator LEDs from outside your power board/box/shelves if you need to troubleshoot. You must have the radio indicators and rockwell light visible from outside the robot, so you may want to mount those separately from the rest of the electronics. Breakers must be accessible for inspection (which means that the inspector needs to be able to get at them with minimal effort, but does not mean that they have to be visible all the time).

You're going to have to change the battery in between matches, so you want that task to be easy to complete. Make sure you secure your battery so it's strapped in and won't bounce around - there's nothing more depressing than a dead robot sitting next to its battery on the field.

You'll need easy access to the cRIO ports to upload any programming changes you make. Also, you have to keep the robot frame electrically isolated from the electronics and the cRIO case is grounded, so don't mount it on metal.

Measure all the components. Make some sketches (or CAD drawings if you're up to that), with reference to the data and power connectivity diagrams so you know what needs to be close to what and where cables are going to be coming out. You also want to pay close attention to the electrical rules (sections 4.1.7-4.1.9), which specify that each motor must have its own speed controller [R50], among other things.::rtm::

You generally want to minimize the length of your power wiring to reduce losses there. Try and avoid "banjo strings" (wiring that is tightly stretched) - you want a little bit of slack in the ends to make it easier to plug them in and to keep the wires from breaking or pulling out of the connectors. Label both ends of every wire with where it's supposed to be plugged in and what's on the other end, and your life will be much easier when you have to troubleshoot problems.

If you want some examples of what teams have managed in the past, there are a fair number of threads here from previous years where teams have posted photos of their electrical boards. Do some searching.

Re: Space for electrical
 

There are ways. Tell your mentor that the battery can go through a top deck. The rule isn't "easily accessible" (though that is a good thing for ease of maintenance); it's that the lights need to be visible. That could be done with Lexan.

And for the speed controller for each motor, I refer you to IIRC, there were 4 Jaguars in the KOP.

Re: Space for electrical
 

thanks so much this is really helpful

Re: Space for electrical
 

Jessica,
The PD can be mounted vertical and speed controllers can be mounted on the opposite side of the mounted PD. You want to be able to see everything. Please keep in mind that the robot dimensions in the rules are maximums. Your robot can be as small as you want to make it to accomplish your tasks as long as all robot rules are met.

Re: Space for electrical
 

Remember that motor controllers need to spaced out so their fans will work, and if you can, mount them so that metal shavings won't end up in them.

Neat electronics get ruined when they catch on fire. ;)

EDIT: I just reread vhcook's post and he noted the vertical spacing. I looked it up here and it is actually 2" for Victors. (I couldn't find anything on Jags better than "adequate air flow" but I imagine it's something similar. I believe since the jaguars vent air out of the sides you need to leave space between them as well, but that's not as important for Victors.)

Re: Space for electrical
 

I don't know about a vertical requirement for Jaguars (if I did do stacked electrical levels, I would leave 2" just as I would have to for Victors, but you should have at least 1/2", optimally 3/4"+ of spacing between Jaguars to allow air flow out of the side vents.

I'd also just like to reemphasize vhcook's point about keeping wire slack.
Make sure to add stress relief points for wires that you expect to move. This not only makes wiring orderly, but also simultaneously ensures that you won't rip or tear wire connections (or even wires themselves) as components move.

If you don't know what stress relief is, all it is tying down the wire at one fixed point (you can use zip ties, cable clamps, spiral wrap, etc) so that it won't shift beyond a certain point. Some people, when running wires through small holes, like to tie a knot in one side so that the knot can't move through the hole, placing a hard limit on how far out the wire can be pulled (useful for ensuring that the connection at the base of the wire never gets stressed).

Re: Space for electrical
 

I would not recommend this. A wire is not a rope. Wires are not meant to tie knots. Doing so moves the stresses from a connector you can see to the wire strands inside of the knot, which you cannot see as they are inside the insulation.

Re: Space for electrical
 

The copper would likely be fine. It is multi-stranded to prevent fractures or breaks from affecting the conductivity. What I would be worried about, though, is the inductor you just made getting hot.

Re: Space for electrical
 

I would not recommend tying knots in wire. You never know how hard you are pulling the knot. Most wire carries a minimum bend radius specification. If you exceed the spec, strands will break. I would suggest that #10 wire with typical 7 strand wire has a minimum bend of 1/4-3/8". Wire with more strands can withstand a smaller radius. The inductance in such a knot is so small at 15 kHz as to be ignored. At 850 MHz or higher, now we are talking some real inductance.

Re: Space for electrical
 

I strongly recommend using a very thin piece of foam over the Jaguar's fan to prevent metal shavings from ruining them. We've been doing this for a while now and it's worked very well, just make sure that air can easily pass through the foam.

Re: Space for electrical
 

A wire that is crossed over itself, like when simple-knotted, self-cancels its inductance. That's why you use a "twisted pair" of conductors, they cancel their inductance because of the crossed magnetic fields.

Oh, and an inductor heats up because of its bulk resistance, not its inductance. But that's beside the point.

The copper would most likely not be fine. Yes it is stranded, but at some point each of those strands is a solid wire, and solid wire breaks when bent. As RufflesRidge mentioned, wire is not rope.

While a knot would be OK in some applications, in FRC the wires are subjected to significant vibration and shock, and most teams would prefer to have high reliability - knotting a wire dramatically reduces its reliability.

If you absolutely must have a 'lump' to prevent a wire from passing through a hole, then adding something to the outside of the wire - a proper strain relief, or perhaps just a wire tie - is a superior choice.