Alternator

[TheAnsweris42]

Apparently someone on my team found an alternator we could use on our robot. While I am severely skeptical about the feasibility of this idea... I can't find anything in the rules that says you can't. Does anyone else know anything about it? I can't imagine that no one else would have tried this before us...

[Sscamatt]

<R51> The only legal main source of electrical energy on the robot is one of the two 12v DC non-spillable lead
acid batteries provided in the Kit of Parts, or a spare of the same part number. The 7.2v “backup” battery is
considered an integral part of the Robot Controller, and may not be used for any other purpose.

[EricH]

Apparently someone on my team found an alternator we could use on our robot. While I am severely skeptical about the feasibility of this idea... I can't find anything in the rules that says you can't. Does anyone else know anything about it? I can't imagine that no one else would have tried this before us...
OK, as far as I know, there is no rule specifically allowing or disallowing alternators. BUT, you need to check costs, size, and weight. You also need to go through the Parts Use Flowchart in Section 5. If you are using it to charge the battery, I'm not sure it's legal. This would be something for Q&A to determine (don't base a strategy around this and have an inspector tell you to take it off kind of thing).

[Sscamatt]

If you are using it to charge the battery, I'm not sure it's legal.

<R52> The EX18-12 Battery may only be charged by a 6 Ampere rated Automatic Battery Charger between
matches. When recharging Kit batteries, you may use the charger provided by FIRST or an automatic charger
with an equivalent charging current rating.


and it would be a custom circuit so:

<R57> The use of additional electronics is intended to allow teams to construct custom circuits for their robots.
The custom circuits may be used to indirectly affect the robot outputs by providing enhanced sensor feedback
to the Robot Controller to allow it to more effectively decide how to control the robot. In addition to the
required branch power circuit breaker, smaller value fuses may be incorporated in the custom circuits for
additional protection. All outputs from the custom circuits must be connected to the analog inputs, digital
I/O, TTL Serial Port, or Program Port on the Robot Controller.

There are many rules against using an alternator

[MikeDubreuil]

If you are using it to charge the battery, I'm not sure it's legal.
First off, you would actually lose more power than you would gain by using an alternator to recharge the battery. Additionally, I don't see how an alternator can pass the Parts Use Flow Chart.
Is the part a motor,
solenoid, pump, or other
actuator?
This would be a Yes. Therefore, you can't use it.

For a more precise answer you would have to tell us the purpose of the alternator.

[TheAnsweris42]

Yeah, I was actually just studying those rules you put up, but I wasnt sure if they applied. Anyways, I think the case is pretty much closed, no alternator. I personally agree with mike about the loss of power anyways. Thanks for the assist

[KenWittlief]

WOW! you got doused with four buckets of ice water, but no one has asked the critical question:

what do you want to use the alternator for?

I can think of applications that might not break the rules.

BTW, an alternator is not a motor, solenoid, pump, or other actuator

an alternator is a device that converts mechanical energy to electrical energy.

[Al Skierkiewicz]

Inquiring minds want to know what you are thinking. On the other hand I don't believe it fits in the rules. Threre may be extenuating circumstances so I would like to hear what you had in mind.

[Al Skierkiewicz]

Off the bat alternating current deals much better with resistance then DC. It's one of the reasons the power company uses it.

This is one of the more confusing myths. The power company uses AC because you can use a transformer to increase voltage. DC power does not pass through a transformer and there is no efficient method of increasing a DC voltage at the power levels we are discussing. For a device consuming 1kW, it doesn't matter whether that is 100 volts DC or 100 volts AC RMS at 10 amps, the power delivered to the load is the same.
For a specific power, using a higher voltage reduces current. Reducing current reduces IR losses and the resistance in miles of delivery cable is devastating to power companies. Imagine delivering 100 MW (100,000,000 watts) at 1000 volts or at 100,000 volts.

[Mike Betts]

Off the bat alternating current deals much better with resistance then DC. It's one of the reasons the power company uses it.

That statement is not correct.

The power lost in in wires is dissipated as heat. In DC circuits, the heating in the wires is purely caused by the resistance of the wire. In AC circuits, the heat is caused by the resistance and the inductance (reactance) (http://www.electrician.com/articles/ampacity.htm) of the wire.

Since more heat (hence more power) is dissipated in AC circuits, DC is the preferred choice based on efficiency alone.

It was the difficulty in switching DC which was one of the deciding factors in the great Nicola Tesla/Thomas Edison "war of the currents" debates in the 1880's.

Edison lost...

Regards,

Mike

[KenWittlief]

the real thing that pushed Tesla ahead wasnt that he invented AC or transformers, or the idea of high voltage transmission lines

the Tesla invention that made all the difference was his AC motor. No one could figure out how to make a motor that ran on AC. Tesla invented the basic AC induction motor concept that is still used today (and patented it)

Westinghouse bought his patent rights for a cool $1M cash + royalites!

House lights and street lights were great, but it was big powerfull electric motors in factories that drove the electrification of the world.

[Biff]

the real thing that pushed Tesla ahead wasnt that he invented AC or transformers, or the idea of high voltage transmission lines

the Tesla invention that made all the difference was his AC motor. No one could figure out how to make a motor that ran on AC. Tesla invented the basic AC induction motor concept that is still used today (and patented it)

Westinghouse bought his patent rights for a cool $1M cash + royalites!

House lights and street lights were great, but it was big powerfull electric motors in factories that drove the electrification of the world.
Tesla also invented the multi phase (read 3) alternator. The patent went to Westinghouse. (Which he later tore up the royalties contract for when Westinghouse was almost bankrupt.) He later went on to study pulsed DC, and the effects that happened when high voltage generators were switched into the distribution lines of Edison's electric plants. (Put on tinfoil hat and check sources when studying what other people say about Tesla.)

[ahecht]

I'm still confused as to why anyone would use an alternator on their robot. If you can't make it through a 2 minute match without running out of battery power, something else is wrong. And, if for some reason you wanted to do something like regenerative braking (and found a way for it to be legal), why would you want AC power on a DC robot?

[KenWittlief]

I am still waiting for "TheAnswerIs42" to come back and tell us what his original application idea was.

he never said what he wanted to do with it

inquisitive minds want to know! :^)

[TheAnsweris42]

Sorry everyone, we had a snow day here and I had to take it off to watch my little sister and brother... dont think anyone made it in the work on the 'bot, the roads here were decidedly reminiscent of a hocky rink.

Anyway the idea was to recharge the battery, I dont think everyone quite understood the work to electricity prinicpal.... but I thought it MIGHT be used for something, and, since we're rookies, like to have my options open... though I'm already worried enough that the build team is overcomplicating... I do the electical for the most part, I dont think I need any more complications on my end either...

[KenWittlief]

so your team mates were thinking maybe you could put an alternator somewhere in the drive train, and it would recharge the battery while the motors were running?

Thats more or less a perpetual motion machine (around here we OBEY the laws of physics [wags finger] :^)

you can do that to some degree with dynamic braking, using an alternator to charge the battery when you want to slow down. Given the 130 second game period that should not be necessary, but if you had a robot that ran all day (running around a factory floor for example) that could be usefull.

I was thinking an alternator has a nice set of bearings, and quite a bit of mass on the rotor, and a built in pulley with a blower. If you took one apart you could possibly use components for a flywheel, a blower/fan, or maybe use the pully assembly as part of a gear train?

The blades on the blower could also be combined with an optical sensor to make a simple speedometer (encoder).

[Kevin Sevcik]

The blades on the blower could also be combined with an optical sensor to make a simple speedometer (encoder).You'd probably be better off tapping off the DC outputs and using it as a poorly calibrated DC tachometer, though.

[KenWittlief]

You'd probably be better off tapping off the DC outputs and using it as a poorly calibrated DC tachometer, though.

we were going to use one of the smaller motors in the KOPs this way, reading the DC voltage being generated (for a shooter in fact, a few years back)

but we could not figure out if using the small motor as a tach this way was legal?

[Al Skierkiewicz]

I was thinking an alternator has a nice set of bearings, and quite a bit of mass on the rotor, and a built in pulley with a blower.

Not to mention a really nice brush and slip ring assy.

[Andy A.]

And plenty of ballest.

If you where underweight, an alternator would solve that real quick. I remeber having to hold one in place while my brother tried to get the bolts in place. It wasn't heavy just carrying it, but try and hold one in an awkward position and you'll know what I mean.

Also, I think that because the whole of the alternator's case is one big ground that it would present a significant safety hazard. I would think that you would have to insulate it somehow, at least from the rest of the bot's frame how ever it is mounted and perhaps even so far so to completly cover any exposed metal.


-Andy A.