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Old 08-16-2008, 01:01 PM   #61
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Originally Posted by Danny/SMC View Post
The majority of the cars use a side by side configuration so this is why we did the pack this way. It also allows us to achieve a higher mAH and C rate. Those who still use a T-Plate car will most likely have to switch to a side by side car as I don't think making a one cell saddle Lipo is feasible.
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Old 08-16-2008, 01:30 PM   #62
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Originally Posted by timmay70 View Post
Not so sure I like the pack in pack idea for rx pack. If one of the batteries decides the world is too much, say rx pack, that is a lot of dead weight you are hauling around. Separate packs will allow you to swap things out if need be. There are also other solutions other than the 350mah heli pack from SMC, although the matching labels would look so cool for those 'designer jeans' types...
I think you've got the right idea. I mean if they are separate then you have the option to move the weight around as needed.

How about lets see if Danny could put the receiver pack, speed control, and a receiver in the case as well. More is always better right?

You're on the right track Danny, but some of the passengers are on the wrong train.

I'll take mine as is. Make that two of them.
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Old 08-16-2008, 01:43 PM   #63
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It's fun to see that everyone has an idea on how things should be with this potentially new class. The goal is to get a Lipo class for 12th scale cars as I believe sub-c cells will be harder and harder to get plus with the improved cycle life and easy manintenance of Lipos this should be the way to go. If this doesn't work there is always sub-c classes.

A reciever pack should not be a big deal as many racers use them or have used them with sub-c packs. Racers can continue to use a 5 cell NiMh reciever pack or go to a Lipo pack.

For those who plan on racing T-Plate cars I'm sorry but we have no plans on doing a single cell Lipo saddle pack as we feel there would not be enough of a market for it. There is a moulding costs for the case and tolling costs for the Lipo cells. Maybe another manufacturer may decide to do one but at the moment we have no plans. The single case pack can and will most likely be used in oval as well as 12th scale.
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Old 08-16-2008, 01:52 PM   #64
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instead of all the receiver pack stuff, can't you run two cell and then limit the motors? Or will that equate to not enough run time?

a 7.2 volt receiver pack plus a seperate 3.7 volt lipo puts you why over the voltage of a two cell (7.4 volt) pack.

My understanding is essentially one pack drives the motor, and the other drives the servo/RX.

Why can't one pack do both?

It seems silly to run a motor on 3.7 volts and the servo on 7.2.
And it is silly. In fact, it's among the worst design ideas I've ever heard. It shows a great lack of understanding among members of the R/C racing industry.

However, it isn't SMC I'm referring to here. SMC is just trying to put a band aid on the problem created by both motor manufacturers and ROAR officials. Those two groups of folks should have commissioned and tested a smaller motor the instant lipo was approved by ROAR for touring car racing - if not earlier.

As Attendee said, limiting the motor and running 2s is the answer. Specifically, limit the motor by making it smaller (if you want to bring the weight down) or by making just the rotor diameter smaller (if you want to keep the motor's weight up).

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Old 08-16-2008, 01:59 PM   #65
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To make a 7.4v Lipo fit in a 12th scale the capacity would be fairly low which. For stock this may work but for mod it may mean runtime issues.
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Old 08-16-2008, 03:07 PM   #66
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I'm pretty dumb about electronics, so forgive me for even asking this...

Is there any way to wire 2 cells in parallel (say, 2 3000 mah cells) so that you get 6000mah @ 3.7V, and then somehow also have them wired in series so you could create 3000mah @ 7.4V for your electronics?
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Old 08-16-2008, 03:13 PM   #67
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Or maybe even some variation of that with 4 1500mah cells? It seems feasible based on how balancing plugs work, but I'm not really that smart about this stuff.
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Old 08-16-2008, 07:19 PM   #68
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I'm pretty dumb about electronics, so forgive me for even asking this...

Is there any way to wire 2 cells in parallel (say, 2 3000 mah cells) so that you get 6000mah @ 3.7V, and then somehow also have them wired in series so you could create 3000mah @ 7.4V for your electronics?
No.

Because if they are wired in parallel, both "+" are connected together and both "-" are connected together. Then if you tried to make a series connection, you would have to connect the "+" of one to the "-" of the other. But since both "+" and both "-" are connected together, as soon as you made the series connection you would be shorting out both cells.

Make yourself a wiring diagram if you want to see this graphically.
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Old 08-16-2008, 07:23 PM   #69
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The balancing plugs allow you to get to the 'inline' connections between the batteries so that you can charge each cell individually to get them to the same level but the cells are still in series.
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Old 08-16-2008, 09:13 PM   #70
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Originally Posted by Danny/SMC View Post
To make a 7.4v Lipo fit in a 12th scale the capacity would be fairly low which. For stock this may work but for mod it may mean runtime issues.
You have the same volume of space and the same weight to work with. Instead of a 5700 3.7v battery you would have a 2850 7.4v battery. In fact, I suspect your manufacturer is actually using two cells to get the 5700mAh capacity, so it's just a question of wiring them the other way.

There's no difference in the amount of energy and power available from those two options. In fact, the 7.4V would provide more energy and power because you lose half as much to resistive loses in the battery, wiring, ESC, and motor.

It's merely a specification in the motor design: halve the kV. Again, the problem here is that there are literally no true brushless motor designers involved with R/C car racing motors.

The reason for that is the prevalence of spec motors. It's usually a good thing for keeping competition tight and costs reasonable, but in this situation it's come back to cost us.
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Old 08-16-2008, 10:27 PM   #71
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I've heard "talk" about people running a 21.5 on a 2 cell lipo, but has anyone actualy tried it? I found a 25C, 1800 2 cell lipo on e-bay for 17$ and will try running it in a rev 5 with a 21.5. (It will easily fit with room to spare in a link car.

Having never even considered running mod 1/12th, I hadn't considered what Danny brought up, which is a valid point if this is to go mainstream. In fact I will be surprised if this 1800 lasts 8 minutes in a 12th with a 21.5. I also have a mongoose to throw into the equation to see if I can find some more real estate and get a lipo cutoff into my 12th for a less expensive and lighter esc.

Are there any 2 cell lipos that fit with in the form factor of a 4 cell that are larger than 1800? Would a 10c 2200 give any more runtime than the 25C 1800?

. . .and one more thing I'll just throw out , not sarcasticly, but seriously asking . . .

. . . would it really be a problem in mod, superstock, or stock, if we had a
7.4v lipo that required adjusting our gearing to make runtime? Or are the 7.4v lipos Danny mentioned, so far off in terms of run time that they wouldn't fit the bill? It seems if the 3.7v pack were discussing here is really 2 2850mah lipos wired in parallel (which is a big if . . .), then would that 2850 wired in series as a 7.4v lipo suffice for 8 minutes of Dumas running a mod if he adjusted gearing?


Hmmmmm . . . .

Danny thanks for the great products and willingness to evolve.

Everyone else, thanks for the responsible discussion. THIS is what RCTech should alsways be like.
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Old 08-16-2008, 11:15 PM   #72
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Andrew, whatever the final package, running into runtime problems with lipo could be expensive. There are pack savers available on the plane/heli market that shut down the throttle signal to the ESC when the pack gets close to empty. Or, a new generation of race ESCs could come out with a useful lipo voltage cutoff built in. I imagine they'd be a must-have if it was possible to fully drain the lipo in one run.

But, yes, that is the other way to limit speed without re-designing motors.
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Old 08-17-2008, 08:11 AM   #73
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The vintage trans am folks are running the 2s lipo / 21.5 combo as a legal alternative to 4 cell / stock. They call a different final drive ratio for this combo to try to equalize things. The vintage trans am folks are pretty proactive about changing the rules to level the field so it's a good place to look.

Most of the new generation brushless ESCs (Castle's Mamba Max and Sidewinders, Novak GTB and XBR, Speed Passion, Tekin RS and R1 Pro, etc) have either selectable or programmable cutoff built in (though none of the selectables I know of have a 1 cell setting).
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Old 08-17-2008, 08:43 AM   #74
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I've been curious about running a single cell lipo, And i think it is feasable In both 4-in-line cell cars, and saddle packs.

I have a small R/C helicopter, that uses lipo's. It is 700mah @ 10C discharge. I've looked at my 12L4, and think that i could fit 6 of these lipo cells in the car. three stacked on each other, in two piles. Normal battery mounting tape would work.

So, what is 6 x 700? 4200 mah. Is that enough capacity for 1/12th?

I'm tempted to buy 3 of these packs (at $12 each), and try this myself.

I've got a few other ideas, and it will be interesting to try out!

Cheers!
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Old 08-17-2008, 08:54 AM   #75
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If you build it they will come.

If I remember correctly, no brushless speedo had any type of lipo cutoff. Now if a single cell cell cutoff is needed,If theres a market (even a small one) for it, there will be a single cell cutoff option. It could be an external unit if need be, they are very small anyway.

Witth 5700mah I'm not afraid to trust my good sense to keep from over discharging, though it has let me down before.LOL
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