SPAM is designing a removable electronics and control box this year. …first time we’ve done it. The interface to the box would be speed controller/relay/solenoid output wiring to motors, compressor etc. and sensor signal input wiring.
We’re looking for ideas for COTS connectors at the interface. Some CD scrounging has revealed AMP Universal MATE-N-LOK connectors for the 12V low power connectors (10 & 4 pins) and Molex Mini-Fit for the high power connector (8-pin).
Ribbon cable seems like a good choice for the signal.
I know there are teams out there who have tackled this in the past.
It sounds like you already have some good ideas Whatever you decide to use, make sure to check it against section 8.3.6 Power Distribution in the rulebook. Pay special attention to the following:
<R42>
The 12V battery, the main 120-amp circuit breaker, and the Power Distribution Board shall be connected as shown in Figure 8-6. In particular: A.
The battery must be connected to the ROBOT power system through the use of the Anderson Power Products (APP) connector.
B.
The APP connector must be attached to the battery with either the copper lugs provided in the FCI Burndy Bag or appropriate lug connectors.
C.
The battery terminals and the connecting lugs must be insulated with shrink tubing and/or electrical tape. D.
The main 120-amp circuit breaker must be directly connected to the hot (+) leg of the ROBOT-side APP connector. Only one 120 amp main circuit breaker is allowed. This breaker must not be bypassed. E.
The Power Distribution Board must be directly connected to the APP connector and main 120-amp circuit breaker. No other loads may be connected to the main 120-amp circuit breaker.
F.
Each primary power connection between the battery and Power Distribution Board must be made with 6 AWG red and black wire or larger.
G.
Circuit breakers must be accessible for inspection at each FIRST Robotics Competition event.
The way i read this rule (which is perhaps open to interpretation) is that you can’t have any intermediate connectors between the battery, the 120 amp breaker, and the power distribution board.
<R45>
All active Power Distribution Board branch circuits shall be wired with appropriately sized wire:
A.
12 AWG or larger diameter wire must be used for all circuits protected by a 40A circuit breaker.
B.
14 AWG or larger diameter wire must be used for all circuits protected by a 30A circuit breaker.
C.
18 AWG or larger diameter wire must be used for all circuits protected by a 20A circuit breaker.
D.
20 AWG or larger diameter wire must be used for the power connection between the Power Distribution Board and the cRIO Mobile Device Controller.
E.
20 AWG or larger diameter wire must be used for the power connection between the Power Distribution Board and the Linksys Wireless Bridge
F.
20 AWG or larger diameter wire must be used for the power connections between the Power Distribution Board and the Analog Breakouts and/or Solenoid Breakout if individual power feeds are used. 18 AWG or larger diameter wire must be used if a common power feed is used for multiple breakouts.
G.
24 AWG or larger diameter wire must be used for providing power to pneumatic valves.
Basically, ensure that all wires (even those in ribbon cables) are of the proper gauge for the load they are carrying.
Other than that, i can’t find any place in the manual that expressly prohibits the use of intermediary connectors for other wiring. Any connectors you do use should be rated appropriately for the maximum load they can provide, and it would be a good idea to keep data sheets for those connectors on hand in case the inspectors question their rating or safety (which is unlikely if you used the proper connectors).
In the past, our team hasn’t used any off the shelf cables for the robot, other than those required to use (programming, tether, radio serial cables in past years, ethernet this year). In the past, we’ve used braided wire sleeving, which is readily available in many diameters and allows you to construct your own organized cables from your own wire.
We’re considering doing this too. I think it might be wise to leave the screw connections for the motor side of the speed controllers, and have the battery connector, power switch (main breaker), and power panel mounted to the removeable module.
If you want to have disconnects for the motors, there are smaller Anderson connectors, also look into what the R/C folks use for quick disconnects for batteries for electric cars, which have to handle current loads similar to the motors we use.
Anderson Power Products makes smaller versions of the Battery connector. They are available in 35 and 45 amp versions and are available at Powerex and West Mountain Radio. The individual insulated bodies can be interlocked to form multipin connectors and they allow for polarity mating. They even come in a variety of colors. I recommend these and the purchase of a crimp tool. (West Mountain) The crimp is sturdy but we add a little solder to be sure of a low resistance contact. You can also use these for control wiring although the crimp tool won’t do smaller wire, soldering is effective. McMaster-Carr also sold these but from a different manufacturer. Similar but not as good.
Some of the students are talking about building a second robot for pre regional practice…I’m more interested in seeing if we can build the first one, first!
Whatever you decide to use, make sure to check it against section 8.3.6 Power Distribution in the rulebook. Pay special attention to the following: