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Old 06-26-2006, 06:54 AM   #1
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Default Receiver pack endurance question

A local track is having a 1 hr nitro race. I have an IB1200 receiver pack. Fully charged will that last the entire hour or will I need to change it mid race? Also any other suggestions? I have raced 20min before but never 1hr. Thank you.
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Old 06-26-2006, 06:55 AM   #2
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I don't know if it matters or not but I use 2 Futaba 9451 Digital Servos.
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Old 06-26-2006, 07:34 AM   #3
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Quote:
Originally Posted by SlickZero.com
I don't know if it matters or not but I use 2 Futaba 9451 Digital Servos.
I would highly recommend going Li-Po. You can't beat this technology for run time.

I run 2 S9550 Digital Servos on both my RRR's with no trouble. The 2 cell 7.4v 1320mAh Li-Po pack from Thunder Power works great!

http://www.hobby-lobby.com/thunderpower.htm

(TP13202 2 Cell 1320 mAh "Pro Lite" 7.4V LiPoly)

Hope this helps.
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Old 06-26-2006, 07:49 AM   #4
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Will 1320 Mah last for a 1hr race? Do you use a voltage regulator? I don't think the receiver and servos are designed for 7.4 volts?
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Old 06-26-2006, 10:48 AM   #5
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You should be fine for a 1 hour race with 1200's.

I know that Spektrum and digital servos do draw more power than analog stuff, but I ran a 1 hour main along with a few minutes of warmup on a 730mah battery. This was using all airtronicsanalog gear. I have made 1 hour with an 1100mah battery using a single futaba digital, analog throttle servo and a spektrum system.

I see no advantage to a lipo receiver pack. I would not get the lipo receiver pack and if you use them you should get the voltage regulator.
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Old 06-26-2006, 11:21 AM   #6
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Thank you Scott. I will give it a try with the 1200mah pack.
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Old 06-26-2006, 11:36 AM   #7
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You won't have any problems with the 1200 pack. I have made one hour mains on the old 850 packs last year.
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Old 06-26-2006, 03:24 PM   #8
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Besides the fact that the Li-Po is alot lighter it will also last longer, especially under load from teh requirements of digital hi-torque servos.

A voltage regulator is not needed in this case. When you fully charge a high Capacity Ni-Mh battery which I have used many times, it's almost the same as the li-po. The li-po under full charge is 8.41V which the spektrum receiver and Futaba Servos handle with no problems.

But, to each his own I suppose....
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Old 06-26-2006, 03:47 PM   #9
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Quote:
Originally Posted by SlickZero.com
Will 1320 Mah last for a 1hr race? Do you use a voltage regulator? I don't think the receiver and servos are designed for 7.4 volts?
Easily. I run 2 digital servos and can run 10-15mins practise, 4x 5min qualifiers with 2mins warmup each and a 30min final on a single 900mah nimh pack.

For Lipo's you do need a regulator but these should come with the receiver pack ready to go. You will get away with 7.4 direct to 2 analogue servos but not most digitals. This is the reason I dont trust Lipo's in cars. The regulator's are fragile and a hard knock can damage the components. That sudden burst of voltage is enough to destroy your nice digital servos which I have seen happen.

A guy argued with me that when a model plane hits the ground it hits with a harder force and Lipo's are used all the time in planes. What he didnt think about was that 90% of model plane fliers use standard $8 analogue servos.
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Old 06-26-2006, 04:09 PM   #10
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You will need a vltage regulator if your running spektrum as LiPo can send 8.4volts to the digitals and then they can catch fire!!
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Old 06-26-2006, 05:02 PM   #11
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What about 800mah lipo battery can handle up to 45 mins main?
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Old 06-26-2006, 06:26 PM   #12
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Ok:

I will not justify what I said.

On the voltage regulator: I cannot say everything about a lipo, because I don't own one. The voltage being read on a nimh battery being 8.4 is probably close to its peak voltage. Once it comes off the charger it drops into the 7 volt range. That is the surface voltage. Once you put it under a load it drops a little more, stabilizes and then discharges as the energy is used. The 6 volt reading that it is given is the nominal voltage. A lipo I believe has a higher nominal voltage. The radio/servo companies as well as Spektrum all recommend using a voltage regulator as they can be damaged by higher voltages. Just because none of your stuff has burned up doesn't mean that you aren't "rolling the dice" with your electronics. The gear was designed to work on 4.8-6.0 nominal voltage. Use the regulator or don't be surprised if you end up with toasted electronics. Second thing I think the regulator does (not sure) is keep you from over discharging your lipo. If you use it too long without recharging, you can destroy the battery as well.

Next: A 1400mah receiver pack (I have now seen 1600's) will last more than long enough. A 1400 nimh has the same energy storage (lower voltage) as a 1400 lipo. I see no reason to change for the sake of changing. I can run all darn day on a 1400.

Weight: The lipo weighs a lot less. In this case I see this to be a bad thing. If the battery sat on the radio tray, that would be different. In most cars the battery is down on the chassis in the center of the car. The best place to have weight. I run a normal nimh battery and my car is already underweight. I removed weight up high and replaced it down low. By using a lighter battery I would be raising the CG. Not a good thing.

In my transmitter a lipo would be great as the thing weighs too much already. In my car I would not use a lipo and I now you have my reasoning. Stick with a good nimh battery and you will be fine. I still see no advantage, and actually see it as a disadvantage to a nimh receiver pack.
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Old 06-26-2006, 07:55 PM   #13
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Quote:
Originally Posted by Scott Fisher
Ok:

I will not justify what I said.

On the voltage regulator: I cannot say everything about a lipo, because I don't own one. The voltage being read on a nimh battery being 8.4 is probably close to its peak voltage. Once it comes off the charger it drops into the 7 volt range. That is the surface voltage. Once you put it under a load it drops a little more, stabilizes and then discharges as the energy is used. The 6 volt reading that it is given is the nominal voltage. A lipo I believe has a higher nominal voltage. The radio/servo companies as well as Spektrum all recommend using a voltage regulator as they can be damaged by higher voltages. Just because none of your stuff has burned up doesn't mean that you aren't "rolling the dice" with your electronics. The gear was designed to work on 4.8-6.0 nominal voltage. Use the regulator or don't be surprised if you end up with toasted electronics. Second thing I think the regulator does (not sure) is keep you from over discharging your lipo. If you use it too long without recharging, you can destroy the battery as well.

Next: A 1400mah receiver pack (I have now seen 1600's) will last more than long enough. A 1400 nimh has the same energy storage (lower voltage) as a 1400 lipo. I see no reason to change for the sake of changing. I can run all darn day on a 1400.

Weight: The lipo weighs a lot less. In this case I see this to be a bad thing. If the battery sat on the radio tray, that would be different. In most cars the battery is down on the chassis in the center of the car. The best place to have weight. I run a normal nimh battery and my car is already underweight. I removed weight up high and replaced it down low. By using a lighter battery I would be raising the CG. Not a good thing.

In my transmitter a lipo would be great as the thing weighs too much already. In my car I would not use a lipo and I now you have my reasoning. Stick with a good nimh battery and you will be fine. I still see no advantage, and actually see it as a disadvantage to a nimh receiver pack.
I totally agree with everything you have said. I use Lipo's in my airplanes for 3D flying due to the weight advantage but in the cars they are really just a disadvantage from the weight issue you pointed out.

My theory has always been to have the drivetrain as light as possible and all upper turnbuckles and pillowballs. Then replace the removed weight to the chassis itself to further improve the cars handling. The easiest way to do that is to use a heavier battery pack.
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Old 06-26-2006, 08:18 PM   #14
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I really dont think center of gravity would change when you remove weight from the bottom of the car only. Now it would if you placed it up top...but otherwise. It is a performance benefit to use the LW AAA packs and Lipos vs the heavier 2/3A packs.

I will say your theories though arent far off though. Yes you want the chassis to have heavier components as low as possible. This is chassis design. But its not a CG problem when you just remove weight at the botton.

Removing weight and having a heavier top will not be a problem. That heavy top your worried about was already there. It might make the car top heavy and it could maybe flip easier....but otherwise reduced weight in a smaller package will allow the car to take to corners faster.

Less weight means the car can change direction easier. CG has nothing to do with it when you goto a LW pack. All a heavy battery will do is itll calm the car down (AKA SLOW IT both direction and forward movement). Another benefit is the LIPO's actually do sit lower than most battery packs. So going with a lipo not only improves every single thing (due to lightening). It also lasts longer.

It makes your cars brakes work better (due to having less weight to slow down)
Accelerate faster (less weight to move forward)
Corner faster (less weight changing direction)
Better tire wear
better fuel mileage

The list goes on and on. Get yourself a LW pack, youll see a big difference. In fact this is one of the suggested mods by HPI themselves for the R40. To go from the larger 1400mah 2/3a packs to a 5cell AAA hump pack. I could tell right away when I did this that the car just became faster all around and quicker in the turns and response.
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Old 06-26-2006, 11:44 PM   #15
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When it comes to determining the center of gravity, where the weight is or is not is very important. Subtracting weight up high is similar (although not exactly the same) as adding it up high. I will exaggerate this example to make my point. Lets say the bottom of the car weighs the same as the top of the car. If you now made the chassis twice as thick and made it out of gold or lead, you would be lowering the cg because now the bottom part of the car would weigh more than the top. If you now made the chassis paper thin and out of balsa wood this would have the effect of raising the cg because now the top half would weigh more than the bottom. You will get a lot more benfit removing weight from your drivetrain (rotating mass) and up high. I have a titanium screw kit on my car, but only the top screw kit. You are changing the relationship of the weight. Top of the car vs. the bottom of the car. Here is my last example of cg and why lowering the weight on the bottom has the same effect as adding it up top:

Think about balancing a wheel. You spin the thing and the heavier side will settle to the bottom. Normally when we balance a wheel, we add weight to the top (lighter side) to try and balance it. We could sand the plastic/metal or grind rubber off to lighten the heavy side. Either way we are shifting the cg.


What you said about making your car lighter and the way it responds has some truth about it. You used a car as an example that is quite a bit over legal weight. Making your car lighter can make it respond better and will certainly make it accelerate and brake better. If all you do is make the battery lighter, you will get a little better power, but raise the cg. Less weight to move gives you a better power to weight ratio. Same with the braking effect. Power to weight has no effect on the cg.

I am in no way saying making the car lighter is a bad thing, but where you remove the weight (and add it if you need to) will definitely effect the handling of the car.
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