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Old 10-19-2008, 02:27 PM   #271
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Andrew,

When we (Oval Racers) went from 6 cell to 4 cell we had to increase gearing by roughly 10 teeth using the same motors, but you figure we dropped 33% of our Voltage.

With the gearing we used at that time, it was about 3 1/2 % per tooth (pinion)

Using that thinking, going from a 4.8v NiMh to a 3.7v Lipo, the loaded voltage of a good NiMh is probably really closer to 4.9v, which would be really close to a 25% drop from the 4 cell, so you'd probably need to gear up accordingly...or use a motor that produces about the SAME Loaded RPM on LIPO as what you were using with the 4 cell pack. (then gearing would probably stay about the same.)

Also, something a lot of guys have not taken in consideration with a lot of the BIGGER Pinions used with LOWER rpms, is that the gear ratios from Tooth to Tooth is lower...much lower.

(example Spur/Pinion 76/57= 1.333 to 76/58= 1.310 = a 1.7% difference. Where a ratio used with HIGH RPM's 120/25 = 4.80 to 120/26 =4.615 which is 4%)
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Old 10-20-2008, 10:49 PM   #272
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Quote:
Originally Posted by Fred_B View Post

For me, LiPo receiver packs are a $20 solution for a $5 problem. NiMh receiver cells are only about $1 each...
If anyone wants for $10 www.CheapBatteryPacks.com can make you a 700mah pack 4.8V AAA sqaure rx pack would be roughly the same weight and size as a Sub-C battery (60g Approx). For $8 you can have a shorter 4.8V 400mah 2/3 AAA pack should space be tight. They are out of the 1/3AAA cells.

I test fit my 4.8V AAA RX pack into my CRC 3.2 and it will into a Sub-C battery slot. If running 3-Cell NiMH that would be my first choice to keep the weight balanced on any car linked or t-plate. For mounting the pack I would end up cutting a scap peice of lexan, kydex, G10, BirchPly, or Carbon to fill that slot and CA into place for provide more space for doublestick tape. I make filler pieces for my oval cars when I like mounting the ESC on the last battery slot.

Nothing wrong with the 5-cell RX packs, just that when everyone is used to 4.8V in 1:12's anyways the extra voltage may make the car more sensitive to steering as the servo will be faster.


I normally order bulk wire and from www.cheapbatterypacks.com 12ga is $1.00 per foot.
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Old 10-20-2008, 10:53 PM   #273
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Originally Posted by SWTour View Post
Andrew,

When we (Oval Racers) went from 6 cell to 4 cell we had to increase gearing by roughly 10 teeth using the same motors, but you figure we dropped 33% of our Voltage.
SW, does the extra gearing account for the lost weight of two batteries or just the reduction in voltage and series resistance?

I do understand that with better batteries and lower voltage that the gearing could be raised some.
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Old 10-22-2008, 11:25 AM   #274
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Originally Posted by ta_man View Post
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.
It would be the oppositte of 2S2P pack essentially. 4P2S configuration. In my searchs for 1:1 elec car conversions 1 of the battery mfg showed different wiring configurations for the same group of cells getting seperate voltage and capacities out of the same group. I'll back track and try to find a link.
Tim
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Old 10-22-2008, 11:37 AM   #275
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Placing both cells in parallel does not short out the cells.. it only doubles the capacity . just like jump starting a car. shorting them out would mean placing a wire between the positive and negative leads amongst an individual cell.. that would be catastrophic!
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Old 10-22-2008, 01:22 PM   #276
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OK. Just a quick question about an rx pack. Can I just run a single cell lipo with the speedo hooked up and have 7.4 or will this mess something up?

Here is what I found to use as a rx pack. Light weight and just pug it in and you get 2 of them for $15 shipped.

http://cgi.ebay.com/x2-Walkera-3-7V-...d=p3286.c0.m14

or

http://cgi.ebay.com/2-PCS-3-7v-400-m...d=p3286.c0.m14

If you want lighter and smaller. It $10 shipped

Thanks for the help,
Joe
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Old 10-22-2008, 01:30 PM   #277
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u can use a 2 cell lipo pack but u will need a 6 volt regilator and disconnect the red wire from the "f" connector that comes from the speedo to the reciever . then plug the flight pack into an open channel.
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Old 10-22-2008, 01:32 PM   #278
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I've been using this:
http://www.horizonhobby.com/Products...rodID=LOSB0862
for about a year now. Using a futaba servo. I've wired a switch and a "reciever" type plug. I leave the little charge plug loose so I can just sit my car on a car stand and plug it in while I work on it. I've gone (2) heats (16 minutes) w/o any problem. I haven't pushed it any further then that. Works GREAT!


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Old 10-22-2008, 01:45 PM   #279
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Originally Posted by John St.Amant View Post
u can use a 2 cell lipo pack but u will need a 6 volt regilator and disconnect the red wire from the "f" connector that comes from the speedo to the reciever . then plug the flight pack into an open channel.
Yeah I have used 2 cell before I just thought to make it easier. I would go with a 1 cell and just plug it in(3.7 from the 1cell and 3.7 from the ESC would make 7.4v). I just wanted to know if I plug in a 1 cell lipo rx pack if it would hurt the ESC or would it be fine. That way I can run a lighter rx pack and not need a voltage regulator.

Thanks,
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Old 10-22-2008, 03:43 PM   #280
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that would be dangerous because the cells would never be at the same voltage and there would be a balance issue. the flight pack would be damaged (due to its smaller capacity and c rating) by the motor drive pack... and it would be realy bad to see a pan car go into melt down in the track.

personally I use a flight power 350mah 2 cell pack.. and the losi 6v 5A regulator. After a prectice, 3 heats and a main , it only used 75mAh . well under the 80% rule. I cherge it once a week using the balance port. never having to mess with it at all.
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Old 10-22-2008, 06:41 PM   #281
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We finally got 2 sample packs with the production verison hardcase which will be 20mm in height with 2 cells in parallel instead of 3.

Were waiting on the cases to get the color transfer then we should get the packs in. The pack will be a 25C/4000.

Novak is working on a booster circuit that would allow us to use this pack without a reciever pack.

Speed control manufacturers will need to lower the cutoff as at the moment when the voltage gets around 3.3v the speed control cuts back power to the motor to save it for the reciever. This feels like your dumping but there is still plenty of runtime in the pack.
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Old 10-22-2008, 07:35 PM   #282
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Excellent news!
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Old 10-22-2008, 08:32 PM   #283
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Great news. I know that the Losi Xcelorin brushless sensored ESC allows you to set the LVC down to 3V, as long as you set it to NiMH mode. Not sure yet if it starts backing off on the motor power. Need one of Danny's packs to start playing with. Any ideas on a release date?
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Old 10-24-2008, 08:19 AM   #284
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Originally Posted by Tubaboy View Post
Danny, is it possible to make the casing only take up 2 of the 4 slots? Then us T-Plate racers can put it on one side, receiver pack on the other side, balance as necessary, and everyone is happy?

Thanks,
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.....thats what i want, so i can run my old junk 12L.........
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Old 10-24-2008, 09:12 AM   #285
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Quote:
Originally Posted by Tubaboy View Post
Danny, is it possible to make the casing only take up 2 of the 4 slots? Then us T-Plate racers can put it on one side, receiver pack on the other side, balance as necessary, and everyone is happy?

Thanks,
Paul
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.....thats what i want, so i can run my old junk 12L.........
I believe you'll be able to just flip the battery over since the top is smooth, and the wires come out the side. That was at least the original plan that Danny told me about in Vegas...
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