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RC8 E-Conversion Questions

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Old 12-28-2008, 09:13 AM
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Hey guys. I've been doing some research on brushless systems, however have yet to come across good documentation on a couple of items yet and I was hoping that someone could help me through the math.

I'm looking at putting the Castle Mamba 2200KV system in my RC8 (club racing).

What I'm trying to determine is what capacity batteries I should be buying. How do you determine approximate run time based motor and battery voltage/amperage?

Do I need a 5000mAh @ 22v to get me through a 20 min main, or will a 2500mAh get the job done? I figure there isn't much point in running a pack that's twice the weight if you don't need it.

I understand that calculations are approximate and vary based on track, etc...


Another question that I don't understand yet. If you have a 22v (6S) system. My reading makes it sound like I could run a 4S pack if I wanted to. I would imagine that the lower voltage would require a high amp draw for such a motor though. Is this an accurate statement?

Thanks guys.

WH
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Old 12-28-2008, 09:30 AM
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Originally Posted by wh7702 View Post
Hey guys. I've been doing some research on brushless systems, however have yet to come across good documentation on a couple of items yet and I was hoping that someone could help me through the math.

I'm looking at putting the Castle Mamba 2200KV system in my RC8 (club racing).

What I'm trying to determine is what capacity batteries I should be buying. How do you determine approximate run time based motor and battery voltage/amperage?

Do I need a 5000mAh @ 22v to get me through a 20 min main, or will a 2500mAh get the job done? I figure there isn't much point in running a pack that's twice the weight if you don't need it.

I understand that calculations are approximate and vary based on track, etc...


Another question that I don't understand yet. If you have a 22v (6S) system. My reading makes it sound like I could run a 4S pack if I wanted to. I would imagine that the lower voltage would require a high amp draw for such a motor though. Is this an accurate statement?

Thanks guys.

WH
If you need 20 minutes you will generally need to run the following setups:

4s 6000 with a 2000-2600kv motor
5s 5000 with a 1700-2200kv motor
6s 3500 with a 1500-1700kv motor

The higher the voltage, the more efficient (think gas mileage) so you don't need as much MAH in the battery.

If you go with the Castle motor, I would suggest the 4s 6000. That 2200kv motor is fairly efficient. You MIGHT make 20 minutes with it, but it will be borderline IMHO depending on your track and how you drive. You will probably be burning about 250-300 mah a minute with that setup so you should be just over 20 minutes of run time.

I ran an RC8 with the Neu 1512 3d and can easily get up to 25 minutes racing with a 5s 5000 pack. With a 5s 4000 pack, I can get right at 20 minutes. With a 5s setup, I am burning about 200-210mah/minute.
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Old 12-28-2008, 09:42 AM
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I was running a Tekno NEU 2200kv motor (same as the CC 2200kv). Same gearing as the RC8 with a 13 tooth pinion. Got three consecutive runs of 27-29 minutes with a 5s 6000mah Polyquest pack. The SC8 is geared the same, and has the same size tires but is alot heavier. I would think a 5s 5000mah would be perfect in a buggy for 20 minutes plus. I have a D8 and run a 2000kv Medusa motor, 15 tooth pinion on 4s 6000mah, I get exactly 20 minutes. Which is not good if halfway through a race the lap counting computer needs to be rebooted or a race restart. Currently thinking a 5s 5000 or the Hyperion 5s 4350 might be what I need.

The forward acceleration on that SC8 was nuts, I was pulling buggies running RB WS7 3's on the straight, but you do get better run times with higher voltage and cooler operating temps.
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Old 12-28-2008, 10:41 AM
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Edumakated,

Thanks for the info.

I'm looking at the Castle 2200kv kit. Most because I figure it would be easy and simple for my first lipo conversion. No one around here does lipo yet, so I don't realy have anyone to lean on.

Why couldn't I run a 6S 5000mah pack? or could I?

Please Edumakate me! =)

WH
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Old 12-28-2008, 10:47 AM
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FG101C,

Thanks for the info. I believe I was reading a little about this, but no one came right out and said it. You are running a 13 tooth on the 5S as opposed to a 15 tooth BECAUSE it's a 5S as opposed to a 4S? Somewhere I was reading a conversation based on gear ratios and pack sizes, but no one ended up explaining it in depth.

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Old 12-28-2008, 10:56 AM
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We should try to keep all of this one thread.
http://www.rctech.net/forum/electric...onversion.html
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Old 12-28-2008, 11:04 AM
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You can run a 6s if you want it to go 80mph. 4s and the 2200kv motor will be faster tan any nitro buggy.
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Old 12-28-2008, 11:10 AM
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badassrevo,

No, I don't need it to go 80mph, and I'm not looking at it from a speed/torque perspective. I should be able to program the ESC to a reasonable level to make things not to crazzy insane. I was looking at it from the perspective that if I run at a higher voltage, then I don't need as high of a capacity pack. Or, if I need long run times, I can run a high voltage and high capacity pack.

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Old 12-28-2008, 11:17 AM
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You are correct, you have a much better grasp on this than most. Get your stuff ordered and go have fun.
I generally try to point people in a direction that is similar in performance to a nitro car so they dont run into heat or breakage (due to speed) issues.
But you have it under controll.
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Old 12-28-2008, 11:31 AM
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badassrevo,

Well, I'm still far from an expert which is why I am seeking advice and trying to gain a better understanding the pros/cons of each approach.

I usually shop at AMain. Was looking at the
http://www.amainhobbies.com/product_...ducts_id/23925

figuring that would make it through just about an amain I would encounter. Then I started considering the weight of such a beast. I didn't really see anything between a 22v 5000mah and a 22v 2600mah (at amain), so I was starting to wonder what kind of run time I would get out of the half capacity pack with the 2200kv motor.

The pro of the half capacity pack is I could lay it flat, ensuring the lowest center of gravity. The kong pack I would have to stand upright to fit.

Not to mention, I could get two of the lower capacity packs for just a little more, which would make it easier from a charging between heats/mains perspective.

Thoughts anyone?

WH
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Old 12-28-2008, 11:54 AM
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Originally Posted by wh7702 View Post
badassrevo,

No, I don't need it to go 80mph, and I'm not looking at it from a speed/torque perspective. I should be able to program the ESC to a reasonable level to make things not to crazzy insane. I was looking at it from the perspective that if I run at a higher voltage, then I don't need as high of a capacity pack. Or, if I need long run times, I can run a high voltage and high capacity pack.

WH
You are correct if you match the motor to the voltage. To second was Badass said, generally you want your motor RPMs to be similar to that of a nitro. Usually between 30-37,000 RPMs. You calculate motor RPM by multiplying the KV by the voltage.

2000 to 2650 x 14.8 (4s) = RPM
1700 to 2000 x 18.5 (5s) = RPM
1300 to 1700 x 22.2 (6s) = RPM

If the RPM is constant, your run time will improve because the higher voltage is more efficient.

When people run 5s and 6s setups, they are doing so with much lower KV motors. Because the lower kv motors don't require as much energy to spin, you don't need as big of MAH pack to get the same runtime as higher kv motors with lower voltage batteries.

Typically, if you are going to run 5s, you want a motor that is 1700-2000kv. 6s setups usually run 1300-1700kv. 4s setups usually run 2000-2600kv.

4s 5000 = 5s 4000 = 6s 3300 in terms of energy stored in the battery. All of these batteries weigh about the same.

You can run a 6s 5000 pack but it is impractical in a buggy because you don't need 30 minute run times and the size of the pack is very heavy
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Old 12-28-2008, 12:16 PM
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Originally Posted by FG101C View Post
Same gearing as the RC8 with a 13 tooth pinion. Got three consecutive runs of 27-29 minutes with a 5s 6000mah Polyquest pack.
Can you elaborate? I'm reading this as almost 90 minutes of run time without a charge?
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Old 12-28-2008, 12:28 PM
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Originally Posted by wh7702 View Post
Can you elaborate? I'm reading this as almost 90 minutes of run time without a charge?
no he means he is constantly getting between 27-29 minutes per run. 90minutes on one charge would be one huge battery or very little power used.
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Old 12-28-2008, 12:34 PM
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Originally Posted by tschenck View Post
no he means he is constantly getting between 27-29 minutes per run. 90minutes on one charge would be one huge battery or very little power used.
Thats what I figured... Just didn't read that way to me...

I have no experience to go off of, so I got to double check these things... =)
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Old 12-28-2008, 01:26 PM
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Personally I think you're better off on 4S with the 2200/kv Castle motor. On 5S it will spin more RPM's than it needs too. Even if you gear it down (which could be an issue in itself as gearing options are limited) the car would have too much power making it harder to control. When you spin higher RPM's the efficiency goes out the window. If you need to make 20 minutes plus, I'd get the 4S 6000mah Poly RC pack. If you want to run 5S or even 6S, look at the lower KV Neu motors.

Also the 2200/kv Castle motor is the longer can (similar to a 1515) so it has a lot of torque to begin with. It should be PERFECT in a truggy. I'm actually hoping Castle releases a thrid motor. On ethat is shorter like the 2650/kv motor (similar to a 1512) but with a 1800-2000/kv rating that would be good on both 4S or 5S.

Best regards,
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