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Old 05-28-2004, 12:03 AM   #1
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Off power rolling effect on motor.

When a car is free wheeling off power what happens to the power created by generator effect of the motor? Would there be any way to feed that power back to the batteries while the car is free wheeling? A doide from the motor + to the batt + and from the motor - to the batt -. Is this a ridiculous idea? If I got it wrong and it in fact would charge the opposite way as in + to - and - to + please say so. I know very little about generators.

My first though was that it would be dangerous since you would be charging your pack every few seconds at possibely dangerous amperage through every run. Thus causing extreme heat, but if you could limit the charge amperage to reasonable levels it could extend runtime a little. I was thinking for 1/12th scale where ever second counts, and there is less draw from the motor but maybe mod TC would benefit.

If this is completely implausible please say so.

disclamer - If your dumb enough to try what I posted before reading the responces I am hoping to get on this topic then you can pay your own medical bills.
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Old 05-28-2004, 12:22 AM   #2
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Call me crazy, but I remember some ESCs somewhere claiming that they automatically did that.... or maybe its 1:30 am and I'm dreaming...
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Old 05-28-2004, 12:27 AM   #3
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Quote:
Originally posted by psbarger
Call me crazy, but I remember some ESCs somewhere claiming that they automatically did that.... or maybe its 1:30 am and I'm dreaming...
You're not dreaming, LRP for example, re-charge while braking. But only while braking, not while rolling with thorttle in neutral.

I believe it's hard to recharge the batt, while the car is rolling. This schotky diode is supposed to eat up the power

If it could be done, I'll bet companies like Tekin, LRP and Novak would already have done it.
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Old 05-28-2004, 12:35 AM   #4
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I think of a doide so that the power from the generator effect of the motor could go to the batt's but no power could go directely from the batts to the motor. "----- |> -----" Since the doide isn't from the motor + to the - it should still push some power through to the batt's and you'll still have more re-charging to the batt's then originally.
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Old 05-28-2004, 01:16 AM   #5
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Fatdoggy,

The generated voltage needs to be greater than battery voltage for any charging to be done, the diode would introduce additional voltage drop that needs to be overcome.
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Old 05-28-2004, 01:16 AM   #6
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Your idea sounds reasonably.... But what about the ESC? The ESC will then have power forced into the output stage.... WHich it DONT like (you can try connecting a batt plus and minus to the output stage of the ESC, if you like ) This is where the schotky diodes come in. We mount it directly on the motor, so it aint affecting the ESC power, but when off-throttle, the motor produces power, but the polarization is reversed, so now the diode start conducting. Thus we ensure there's only a very low reverse voltage (0,1-0,2 volt, I believe) on the ESC out put stage.

Even if you mounted some relays to re-direct the current, think of this: Charging the battery, will act as a load on the motor, resulting in a huge braking effect.... It's similar to dead short the motor (the batts are amp hungry ! ), which is what the ESC do while braking.
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Old 05-28-2004, 01:17 AM   #7
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Quote:
Originally posted by rough512
Fatdoggy,

The generated voltage needs to be greater than battery voltage for any charging to be done, the diode would introduce additional voltage drop that needs to be overcome.
This would only be 0,6-1,0 volt, depending on the amp rate. But how high is the voltage output from the motor? Unloaded it's pretty high, but loaded, I believe it'll adapt to the battery voltage/amp draw.
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Old 05-28-2004, 02:03 AM   #8
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Rough, Cole - Thanks for the input. So even if the voltage output of the motor was higher then the battery voltage after factoring the doide draw(pretty unlikely), when off power you'd still get a drag braking effect on the motor.

Quote:
Originally posted by Cole Trickle
Even if you mounted some relays to re-direct the current, think of this: Charging the battery, will act as a load on the motor, resulting in a huge braking effect.... It's similar to dead short the motor (the batts are amp hungry ! ), which is what the ESC do while braking.
Even if you dropped the timing on your motor and upped your rollout you could slightly lessen the effect of the"timing" drag brake, but would that then drop the motors output voltage?(amp output would definately drop). You'd still have the batt's drawing from the motor causing a big drag brake effect..

Cole - If a schotky diodes wasn't used(I never use them between the motor + and -) would this effect anything?

Thanks for bearing with me, I'm not exactely hip with electronics.

Last edited by fatdoggy; 05-28-2004 at 02:15 AM.
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Old 05-28-2004, 02:44 AM   #9
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Back in the 80's there were speed controllers which claimed to offer "regenerative charging" by using the motor braking to recharge the batteries.

IMHO any attempts to do this with the current batteries on offer is a waste of time and money. I race a lot of 1/12th scale modified and I have to be driving pretty badly to get close to dumping.

Additionally, any "home grown" solution would add weight to the car, which in turn would require more power to get it round the track.. catch-22
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Old 05-28-2004, 04:32 AM   #10
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Quote:
Originally posted by fatdoggy
Cole - If a schotky diodes wasn't used(I never use them between the motor + and -) would this effect anything?
The main issue would still be the big amount of drag brake...

I think you're lucky, that your ESC's havent blown....

Personally, I hate any kind of drag brake... I sometimes consider using one-ways all over, and then have disc brakes for braking... Eventually one disc brake pr. diff, so you could adjust amount of braking front versus rear.... But I neither have the time, nor the equipment for doing this....
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Old 05-28-2004, 08:28 AM   #11
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the speedos you guys are speaking about were produced by tekin back in the late 80's and early 90's i had them and i still have three of them sitting in my collection
the models were the 411g 411 p and the 9g these would regenerate a charge from running a little drag brake. I didnt run drag brake even though i didnot run drag brakes i did notice a 5 to 10 second increase of run time with those speedos.

the only reason i stopped running those speedos was the size and the lack of a repair facilty.
now that tekin is back i will be running their stuff.
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Old 05-28-2004, 05:10 PM   #12
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Hmmm, this is getting interesting, looks like I will be sending over an email to my AP Physics II teacher... , if he can produce an explanation (not like he races rc cars and messes with ESCs) then I will post what he says on here.
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Old 05-28-2004, 05:47 PM   #13
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Cole - Keyence esc's advise against using schotty diode on the motor, I think they already have one internally. With the disc brakes I've also though about that, the only problem would be that you'd need 4 disc brakes/one each wheel, also you'd need to keep ball dif in the back or the car would handle like crap, now if a limited slip rear dif was invented for r/c that disengaged and free wheeled off power...

speedxl - Thanks for your input.

=MisFitz= NuKe - Cool!
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Old 05-29-2004, 09:55 PM   #14
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found this page on the novak website.

http://www.teamnovak.com/Tech_info/e...min/index.html
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Old 05-29-2004, 10:02 PM   #15
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that diode idea is very interesting...

try an LED and run your car outside...

see if the LED lights up when you break...
If it does you know it has to work
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