[techhelpbb]

I think it's probably important to frame this for the reader as to the advantages and disadvantages:

1. Use a portable computing device that is designed with an integral battery:

Advantages (limiting this only to the power issue):
A1. No effort to design additional power circuits required.
B1. Complete isolation from the battery used to power the robot motors.
C1. Battery life that will exceed 30 minutes.
D1. Easily replaced year on year (performance advantages outside scope).

Disadvantages:
A2. Limited opportunities to reduce the weight of the unit.
B2. Something else to remember to charge.
C2. Limited shelf life.

2. Create a battery powered COTS version of various boards like the Raspberry Pi, Arduino, BeagleBone, Panda...

Advantages:
A1. No effort to design additional power circuits required.
B1. Complete isolation from the battery used to power the robot motors.
C1. Slips past FIRST approval process if it is legal to do at all (unknown criteria).
D1. Allows weight tuning to optiminal levels.
E1. New market territory as not many things like this exist.

Disadvantages:
A2. We don't know how far you have to go to make something like this a COTS portable computing device. You might have to include parts at the time of sale that can be removed later to reduce the weight.
B2. You get whatever you get power wise. How long is long enough to run on battery? If your target market exceeds FIRST there's a real design issue in battery run time.
C2. Cost - you are bundling the cost of the computing device into the cost of the battery package. You must absorb both costs at the time of manufacturing and stocking.
D2. New market means uncharted territory and risk.

3. Create a super capacitor based circuit to provide isolated power to whatever you connect to it:

Advantages:
A1. No effort to design additional power circuits required.
B1. Potentially complete isolation from the battery used to power the robot motors.
C1. You can provide power to whatever works within those limits increasing the target market.
D1. If a new version of a computing device ships you don't care as long as it needs the same power.
E1. Super capacitors do not contain as many nasty or volitile chemicals.
F1. Bleeding edge market opportunity.

Disadvantages:
A2. Don't know if FIRST is willing to approve something like this.
B2. Approval is a process that commits the maker to certain requirements.
C2. The cost of the super capacitors mean this will likely cost at least $15 but more likely closer to $25.
D2. Super capacitors generally will provide less run time then a battery for the same volume.
E2. Cannot be expanded with a mere pass transistor - besides it stores power not merely regulates the power.
F2. Bleeding edge markets might leave the seller bleeding.

4. Use a step-up then step-down power supply:

Advantages:
A1. Limited effort to design the power circuits.
B1. Cheap - There are piles of Chinese boards for this on E-bay and through North American / EU supply houses.
C1. The power supply maker doesn't lock you into a computing board as part of the package.
D1. When the robot is off this will not hold power very long.
E1. Can retain operation at proper output voltage down around a 3V robot battery.
F1. Someone could mitigate many of the disadvantages below just be bundling these items into a COTS item.
G1. If FIRST requires approval for this at least it has wide potential market.
H1. At least 85% efficient and easily past 90% efficient.
I1. It is possible to exploit existing power supply circuits in the PDB to achieve the first stage regulation.
J1. Good isolation but when the input from the battery is charging the output filter of the first stage noise can pass.
K1. The odds of 2 separate regulators synchronizing with the noise on the robot battery are very low.

Disadvantages:
A2. Very few COTS step-up then step-down modules prefabricated (boost - buck)
B2. Generally single stage (boost - buck) converters have lower power limits than 2 seperate systems chained.
C2. The circuits themselves are much more complex than a 7805.
D2. End user packaging is probably required.
E2. If someone bundles this into a COTS item FIRST may require approval for it.
F2. Regulation can not be expanded with external pass transistor without inheriting the disadvantages from next choice..

5. Use a simple 7805, 7809, 7812 or adjustable reference regulator:

Advantages:
A1. Simple.
B1. Generally a small circuit.
C1. Cheap - most of the car power supplies that output 5V are 7805.
D1. A low dropout version will work to fractions of a volt at the input over the output voltage.
E1. Great for limited currents.
F1. Low weight when the current limits are low but high currents require heat sinking.
G1. If you use mica insulators you might be able to heat sink to an aluminum or copper robot component.
H1. Available in various packages with various current limits: surface mount, TO92, TO220, TO3
I1. It is possible to exploit existing power supply circuits in the PDB to provide initial regulation to reduce heat.
J1. It is possible (but counter-productive) to make a circuit to bypass the regulator if the input voltage drops lower than the regulator input voltage requirements.

Disadvantages:
A2. Gets rid of excess energy as heat.
B2. Increased current demands increases the heat generated.
C2. At increased currents needs a heat sink so weight increases unless you can manage to use the robot components as a heat sink.
D2. Does not deal with highly inductive or capacitive loads well.
E2. Can sustain physical damage under high loads.
F2. Can not produce a higher voltage than available at the output.
G2. Versions that are not low drop out require at least 1V more at the input than the regulated output.

Comments or suggestions let me know.