Alternator

[Blake_Ross]

@sabydady

Yes, but the point Im trying to make is that you dont necessarily need gasoline to power your alternator, you could power it from an electric motor or a wind turbine

@devinc

that is EXACTLY what im trying to say

Not on a Vex Robot operating in a typical indoor environment.

On a car it would be possible, but not useful, to use a wind turbine.

On a car it would be just plain silly to use an electric motor [Edit]to drive an alternator\Edit].

Blake
PS: I’m finished - If someone else wants the last word they are welcome to it.

[devinc]

the new Nissan Leaf’s use an all electric motor.

[dontworryaboutit]

@devinc

the new Nissan Leaf’s use an all electric motor.

They have a battery, too, which requires charging. Vex robots use all electric motors, just like the Leaf, so why should they be allowed to run without charging?

I think the point is that you have a certain amount of energy going into any vehicle, and due to friction and work, you will never get that energy back into the vehicle once it has been used.

[devinc]

i think everyone thinks that im trying to make our robots onto an infinite loop of power, i know that that is not possible but it would be nice have our batteries be able to last a bit longer

[murdomeek]

define “a bit”
do you mean 150% increase?
125%?
120%?
101%?
because maybe people are mistaken that you want say 150%
but maybe they are trying to say that realistically, you can only get around 102% (made up numbers)

thats just the response i get when im reading this thread

[anon50541363]

@gblake

Where will we mount (on the robot) our internal combustion engines that we will use to turn our alternators and thereby convert stored chemical energy (presumably stored in hydrocarbon fuels) into mechanical energy into electrical energy into stored chemical energy (stored in the battery chemicals)?

Blake

Very nice.

-Cody

[sabydady]

@devinc

i think everyone thinks that im trying to make our robots onto an infinite loop of power, i know that that is not possible but it would be nice have our batteries be able to last a bit longer

Its just not possible. The alternator would take more power from the battery than what it will put back in.

The problem here is that your thinking that the alternator represents no effort for the electric motor.

The alternator is a load greater than what it can produce, so as I mentioned in the earlier post if you want to get 1 watt from the alternator you need to feed it more than 1 watt.

[Chris_is_me]

How a car alternator works: Something other than the battery is powering the wheels. Part of that energy from something other than the battery is used to charge the battery.

How a Vex alternator would “work”: The battery powers the motors. The battery is used to… charge itself?

[DinerKid]

@murdomeek

define “a bit”
do you mean 150% increase?
125%?
120%?
101%?
because maybe people are mistaken that you want say 150%
but maybe they are trying to say that realistically, you can only get around 102% (made up numbers)

thats just the response i get when im reading this thread

You could not get more. Any amount more… You would be creating energy…

~DK

[Delta]

Once you use you battery’s potential energy by running your motors, you can either use that kinetic energy to move your robot, or transfer that kinetic energy back into potential energy (via an alternator). You can’t do both, the laws of physics (which are lame) don’t allow it. Not to mention that friction would take a massive tole on the cycle.
“You can’t have your cake and eat it too.”

Delta

[mbrunn]

just charge your batteries alot! the matches are not that long!!!

[Quazar]

@DinerKid

If i am not mistaken when the robot is rolling forward as you described (no motor power just coasting forward due to momentum) you are actually using the motors as generators. I mean we have all manually pushed down our robot arm when the motors are plugged in and seen how the micro-controller lights light up, i am not sure about the wiring inside of the micro-controller but it is possible that we are actually charging our batteries a bit when we coast to a stop.

I don’t know exactly how many FIRSTers there are here but my team joked around this year about our mini-bot charging up a bit every time it coasted down the pole after the off switch was triggered at the top of the pole.

Just did a quick test, and thought I’d post some numbers. A Cortex with a single 3-wire motor consumes about 150mA from the battery. By hand-turning the motor pretty hard, I was able to get that to drop down to about 50mA. If you had multiple motors all being externally driven (momentum, or being pushed), the current flow from the battery would reverse resulting in some charging…

I don’t know how efficient the charging would be, since the power flow isn’t being managed for efficient charging. But, it seems that Vex robots already employ a form of regenerative braking.

Cheers,

• Dean

[DinerKid]

@Quazar

Just did a quick test, and thought I’d post some numbers. A Cortex with a single 3-wire motor consumes about 150mA from the battery. By hand-turning the motor pretty hard, I was able to get that to drop down to about 50mA. If you had multiple motors all being externally driven (momentum, or being pushed), the current flow from the battery would reverse resulting in some charging…

I don’t know how efficient the charging would be, since the power flow isn’t being managed for efficient charging. But, it seems that Vex robots already employ a form of regenerative braking.

Cheers,

• Dean

Wouldn’t the voltage have to be higher than the battery voltage though in order to charge it up?

~DK

[octanetripledax]

@DinerKid

Wouldn’t the voltage have to be higher than the battery voltage though in order to charge it up?

~DK

Yes. Voltage is the potential difference between two things, in the case of charging a battery you want the difference to be positive. That’s why battery chargers usually charge the batteries by pumping in a higher voltage than the nominal of the cell.

[DinerKid]

@octanetripledax

Yes. Voltage is the potential difference between two things, in the case of charging a battery you want the difference to be positive. That’s why battery chargers usually charge the batteries by pumping in a higher voltage than the nominal of the cell.

So in order to get some type of regenerative braking/coasting out of your robot the wheels would have to be coasting and turning the non-powered motors with them at a speed higher than the speed that the motors would drive them in order to produce a higher voltage than the battery voltage. The only way i see this happening would be coasting down a ramp or being pushed by another robot that drives faster than yours and has a beefy drive-train.

~DK