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Old 03-25-2012, 08:12 AM   #1
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Default LiPo: shorty pack vs. standard packs

I need to shave weight off my rc. I have come to the conclusion that the battery is really my last option. I have looked into different options and what "feels" best is a shorty pack.I checked the ROAR rules and it only states "maximum" dimension, not minimum.

The maximum dimensions are:
Length: 139mm +0mm/-3mm
Width: 47mm +0mm/-2mm
Height: 25.1mm +0mm/-3.0mm

What are the benefits/drawbacks to running a shorty pack? I am running RCGT, and 7.5R just for fun.
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Old 03-25-2012, 01:44 PM   #2
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Originally Posted by silverhkswrx View Post
I need to shave weight off my rc. I have come to the conclusion that the battery is really my last option. I have looked into different options and what "feels" best is a shorty pack.I checked the ROAR rules and it only states "maximum" dimension, not minimum.

The maximum dimensions are:
Length: 139mm +0mm/-3mm
Width: 47mm +0mm/-2mm
Height: 25.1mm +0mm/-3.0mm

What are the benefits/drawbacks to running a shorty pack? I am running RCGT, and 7.5R just for fun.
Only real drawback is runtime; biggest capacity is about 4400mah compared to 6000+ for full-size packs. For racing this won't generally matter, even with a 10.5 boosted TC I only use 2500mah. But for bashing the reduced runtime could reduce the fun!

There's no loss of performance compared to a bigger pack; did some tests this week comparing a Reedy shorty lipo against a 5800mah 60C pack and the speed and current were identical (with 13.5 boosted motor).
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Old 03-25-2012, 01:55 PM   #3
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Also depends on your car too. If you have a car with the pack mounted either on the left or right side, it will affect weight balance too. Of course, if the pack runs down the middle, then you have the advantage of distributing the weight around to suit driving conditions.

I'm looking at getting a shorty lipo for one of my F1 cars to not only allow room for electronics, but for a more rear weight bias to increase rear grip on a 2WD car.
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Old 03-25-2012, 02:24 PM   #4
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Originally Posted by Dan View Post
Also depends on your car too. If you have a car with the pack mounted either on the left or right side, it will affect weight balance too. Of course, if the pack runs down the middle, then you have the advantage of distributing the weight around to suit driving conditions.

I'm looking at getting a shorty lipo for one of my F1 cars to not only allow room for electronics, but for a more rear weight bias to increase rear grip on a 2WD car.
I am running a Tamiya TA06 and with a full size lipo, it is 1323g with a full size 240g lipo. I have found some at 203. I just didn't know if the size had any correlation to punch. My chassis needs all the help it can get. Im even thinking of changing the esc with a bottle of Hydroxycut to cut weight...
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Old 03-25-2012, 09:24 PM   #5
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Why the fascination with weight cutting? My limited experience shows light cars don't handle very well road racing...
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Old 03-25-2012, 09:34 PM   #6
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Why the fascination with weight cutting? My limited experience shows light cars don't handle very well road racing...
I am trying to balance the car better. If I cut enough, I can play with the balance better.
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Old 03-25-2012, 10:28 PM   #7
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Default Unbalanced

Most race tracks have a high-speed sweeper at the end of the straight. Loading the inside of your car, a la offset Sprint Cars, improves control and keeps your speed up. Plus there will be many more turns in that same direction. Slower infield turns don't shift the weight so hard, so aren't effected as much by imbalance. No charts or graphs, but experience says a 50/50 side-to-side balance is often not the fast way to go...
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Old 03-26-2012, 08:32 AM   #8
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The chassis I am running is a ta06 and it is center mounted battery.this will help immensely.
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Old 03-26-2012, 08:39 AM   #9
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Ahh, yes.
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Old 03-26-2012, 08:55 AM   #10
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Quote:
Originally Posted by Laguna Bozo View Post
Most race tracks have a high-speed sweeper at the end of the straight. Loading the inside of your car, a la offset Sprint Cars, improves control and keeps your speed up. Plus there will be many more turns in that same direction. Slower infield turns don't shift the weight so hard, so aren't effected as much by imbalance. No charts or graphs, but experience says a 50/50 side-to-side balance is often not the fast way to go...
I have to disagree. While a biased weight may improve a few turns it makes the car unpredictable and twitchy. Your comparison to sprint cars in interesting but not valid for road racing. You won't find a full size road race car with a weight bias to one side or the other. Remember most of the slower infield turns are also more extreme then a sweeping 90. These turns may be slower but they are usually much more aggressive so the weight will shift just as much if not more.

A lighter car will also accelerate faster out of the turns and brake better going into the turns. Suspension adjustments can be made to adjust for a lighter chassis. If a heavier car was the better option then we would have maximum weight limits not minimums
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Old 03-27-2012, 05:07 AM   #11
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Quote:
Originally Posted by Laguna Bozo View Post
Most race tracks have a high-speed sweeper at the end of the straight. Loading the inside of your car, a la offset Sprint Cars, improves control and keeps your speed up. Plus there will be many more turns in that same direction. Slower infield turns don't shift the weight so hard, so aren't effected as much by imbalance. No charts or graphs, but experience says a 50/50 side-to-side balance is often not the fast way to go...
Disagree. I want my car to pull straight on the power and under braking, which requires a 50/50 split. I want it to handle the same on LH and RH corners, which requires a 50/50 split.

A car takes about 0.5s to get round a sweeper, and 13s to get round the rest of the lap, so I'm going to optimise it for the 13s chunk, not the 0.5s chunk.
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Old 03-27-2012, 05:54 AM   #12
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Disagree. I want my car to pull straight on the power and under braking, which requires a 50/50 split. I want it to handle the same on LH and RH corners, which requires a 50/50 split.

A car takes about 0.5s to get round a sweeper, and 13s to get round the rest of the lap, so I'm going to optimise it for the 13s chunk, not the 0.5s chunk.
hm.. i thought a slightly heavier rear end would do some good? right now my car is 50.25% rear that translates to 21g heavier at the back, and it handles superbly without losing rear traction even in the tightest turns. These shorty packs are worth a try on my old school 414 type TC to cut weight.
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Old 03-27-2012, 06:21 AM   #13
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hm.. i thought a slightly heavier rear end would do some good? right now my car is 50.25% rear that translates to 21g heavier at the back, and it handles superbly without losing rear traction even in the tightest turns. These shorty packs are worth a try on my old school 414 type TC to cut weight.
They are talking about L/R balance.
F/R has more to do with driving style and personal preference. My JRXSR is almost 54/46 the way I have it laid out, but I would imagine I could get it much closer to 50/50 if I wanted.
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Old 03-27-2012, 06:51 AM   #14
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You won't find a full size road race car with a weight bias to one side or the other.
For the most part yes but technically not true. There are many road race cars out there with a side bias either intentionally or due to rules.
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Old 03-27-2012, 09:33 AM   #15
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For the most part yes but technically not true. There are many road race cars out there with a side bias either intentionally or due to rules.
Exceptions to every rule.
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