Motors generating power

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Posted by Patrick Dingle at 2/10/2001 11:03 PM EST


Coach on team #639, Red B^2, from Ithaca High School and Cornell University.



Our team made an interesting observation while pushing our robot around... The LEDs on all the victors lit up, and the fans even started spinning (with no battery attached). Does anyone know why electricity generated by the motors would light up the victors. This is especially strange considering it is a power OUTPUT. Anyone know why?

Patrick

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Posted by Joe Johnson at 2/10/2001 11:08 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: Motors generating power
Posted by Patrick Dingle on 2/10/2001 11:03 PM EST:



Don't know the entire reason why, but this is a very
common thing. Happens to all of us. It even happens
when you put your arms down (if you have any).

It seems like the H bridge that the Victors use must
also allow the motors to act as generators.

Joe J.

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Posted by Dan at 2/11/2001 2:10 AM EST


Other on team - from Carnegie Mellon sponsored by -.


In Reply to: very common
Posted by Joe Johnson on 2/10/2001 11:08 PM EST:



Is it possible the victors allow regenerative braking (ie motors charge the batteries when backdriven)? When those LEDs light up they need 12ish volts, right? Maybe I should use mine for an electric bike or scooter, with all the hills in Pittsburgh the regenerative braking may come in handy.
Dan

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Posted by Alan Nickerson at 2/11/2001 7:41 AM EST


Engineer on team #157 from Assabet Valley R.T.H.S..


In Reply to: Re: very common-Regenerative Braking?
Posted by Dan on 2/11/2001 2:10 AM EST:



It's becasue the Victors allow dynamic braking. The H-bridge is controlled with a PWM signal. Without the control signal the H-bridge defaults to one direction and the motors energy is then directed through the Victors circuitry making the lights blink.

My 2 cents worth

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Posted by Alan Federman at 2/11/2001 9:33 AM EST


Engineer on team #255, Odyssey, from Foothill HS, San Jose and NASA.


In Reply to: Re: very common-Regenerative Braking?
Posted by Alan Nickerson on 2/11/2001 7:41 AM EST:



Here is am experiment you can try at home. Turn off your robot - and remove the leads from the PWM that go to a motor. An arm or wheel that you can drive by hand
FP or van door - move the arm back and forth. Now short the leads together and try the same thing. Is it
easier or harder to move the motor?


Now you now how the brake/coast mode works on the Victors.

Second home experment - if you have some Lego motors,
connect two of them together - try spinning the shaft of one and watching the second. What happens? Can you
explain it?

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Posted by Shawn McMahon at 2/12/2001 5:15 PM EST


Student on team #263, Aftershock, from Sachem H.S. and Symbol, Citycorp., Apoge, CA ....


In Reply to: Re: very common-Regenerative Braking?
Posted by Alan Federman on 2/11/2001 9:33 AM EST:



This electrical feedback is why the vicotrs w/ the red lable need a diode. Without the diode the feedback is capable of damaging the victor. The red ones were used in 99 competion. Last year as well as this year we have the blue victors. They have a built in diode type device (H bridge) which keeps the victor from being damaged but lets the power leak though to the other side.

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Posted by Joe Johnson at 2/12/2001 5:49 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: Red vs Blue
Posted by Shawn McMahon on 2/12/2001 5:15 PM EST:



My understanding of the reason for the zener was not to protect the Victor, but to protect the other electronics.

That is what I recall from conversations with Tony, et. al. at Innovation First, but I could be wrong.

Joe J.

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Posted by Shawn McMahon at 2/15/2001 7:45 PM EST


Student on team #263, Aftershock, from Sachem H.S. and Symbol, Citycorp., Apoge, CA ....


In Reply to: Diodes? Diodes? Victors don't need no STINKIN' DIODES!
Posted by Joe Johnson on 2/12/2001 5:49 PM EST:



Sorry, they're not diodes. But I do remember something about them being like the zener diodes Joe Johnson mentioned. I know they are not the diodes that come in the kit. Those are 1 way LEDs. Big difference. They do make a nice flash when someone blows one. :-)(Not in robotics, in electronics classes) I'm pretty sure the transorbs protect the speed controller. Don't quote me on it but they would be the most sensitive equipment. Forcing current back though them would charge your battery or at least power your fuse box to make a few fans spin. I don't know exactly how they are constructed but perhaps they could send voltage back to the controller? Otherwise I'd say it would be to protect the sc itself. I'm I right? Wrong? ... always learning

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Posted by Ed Sparks at 2/13/2001 1:34 PM EST


Engineer on team #34, The Rockets, from Bob Jones High / New Century High and DaimlerChrysler.


In Reply to: Red vs Blue
Posted by Shawn McMahon on 2/12/2001 5:15 PM EST:



The devices that are required with the red victors are NOT DIODES! They are in fact a transorb which is a device that absorbes electrical "spikes" on the power lines and converts that energy to heat. If you put a diode (such as those in the kit) across the power lines to the Victor, and happen to install it such that it is forward biased, smoke will escape, the diode will become a lump of goo, you will be confused, the flash will stun you, but the Victor will probably be alright! Use TRANSORBS from Innovation First if you are using RED Victors.

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Posted by Al Skierkiewicz at 2/13/2001 2:04 PM EST


Engineer on team #111, Wildstang, from Wheeling High & Rolling Meadows High and Motorola.


In Reply to: Red vs Blue
Posted by Shawn McMahon on 2/12/2001 5:15 PM EST:



The two leaded devices are not diodes. See Ed's entry. The transorbs are intended to squash spike voltages generated by the motors from damaging the microcontoller in the speed controller. A rapid change in direction(standard for competition) on the motor is capable of producing a rather short but high voltage pulse that exceeds 12 volts.
Theoretically if the motors were turned at the same speed as your top speed they should produce about 12 volts. Since there is no power supplied to the speed controllers with the power turned off, the FETs that switch current to the motors, look like resistors. Drive the motor by pushing and voltage is generated, current flows through the FETs and appears at the input terminals of the controllers.
Al

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Posted by Joe Johnson at 2/13/2001 4:23 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: Not Diodes
Posted by Al Skierkiewicz on 2/13/2001 2:04 PM EST:



Somehow I got in my head that the transorbs were more or less zener diodes back to back (or front to front).

My understanding is that zener diodes are just like regular diodes but they begin to conduct and act like resistors when subjected to reverse voltages above their rated voltage.

By putting two zeners in series facing opposite directions, they work together to clip the spikes in voltage.

Am I all wet on this one? Remember I am an M.E. by training.

Joe J.

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Posted by Ed Sparks at 2/13/2001 4:59 PM EST


Engineer on team #34, The Rockets, from Bob Jones High / New Century High and DaimlerChrysler.


In Reply to: Transorbs = Fancy Zeners?
Posted by Joe Johnson on 2/13/2001 4:23 PM EST:



My belief is that these devices are more or less MOVs (Metal Oxize Variable Resistors). This type of device is a resistor that lowers it's resistance as the voltage across it's leads increases. At low voltages it is practically an open circuit, however, if a short high voltage spike wanders along, it lowers it's resistance and absorbs it's energy (converting this energy to heat). These things are in all of your better power strips to keep those nasty household spikes at bay. They are usually red in color and disk shaped (something like a ceramic capacitor).

The reason I jumped on this thread was that someone may try to use one of the kit diodes as a transorb and that could be an unfortunate experience.

Hope this helps.