Savage project idea. Please read have many ?'s!

[BL_RV0]

Thanks again, Othello. I had a new idea- a Mega 22/45/3 on 12s A123 with 15/49 gearing. The /3 is 1000kv versus the 1380kv of the /2 wind. One problem though- the /3 wind only pulls 35a maximum versus the /2's pull of 60a maximum. Would this result in less torque? Should I stick with the 22/45/2 and 12s and gear down, since you say that the extra 2s make a large difference in runtime?

[lutach]

Originally Posted by BL_RV0

Thanks again, Othello. I had a new idea- a Mega 22/45/3 on 12s A123 with 15/49 gearing. The /3 is 1000kv versus the 1380kv of the /2 wind. One problem though- the /3 wind only pulls 35a maximum versus the /2's pull of 60a maximum. Would this result in less torque? Should I stick with the 22/45/2 and 12s and gear down, since you say that the extra 2s make a large difference in runtime?

The AMP rating of the Mega are based on continuous (Very conservative) use. It will handle short bursts just like any other motor.

[BL_RV0]

Ok. How does the idea of a 22/45/2, CC HV85, 10s a123, 13/49 gearing, and a 3 speed transmission sound? Also, any guesses how much this thing will weigh?

[othello]

Both motors are able to generate the same amount of torque, but the motor with more winds (ACn22/45/3) will need less Amps to generate the same amount of torque as a ACn22/45/2. Theoratically 1000 vs 1380kv = 38% less Amps. Meaning a ACn22/45/3 drawing 30A at a given voltage would require your ACn22/45/2 to draw 41,4A to generate the same amount of torque. This is how i understood it.

The ACn22/45/2 with 1380kv would be a relative hot motor on 10s1p A123. Under load at full speed voltage of 10s1p A123 will drop to 28-30V. Giving you rpms of around 40000rpm. Seems a bit high for my liking in a heavy truck. I used a Neu 1512/2Y (1400kv) in my 9lbs buggy and saw rpm levels of up to 44000rpm (with 10s1p A123). Which seems alright for a lighter buggy. The same motor in my heavier truggy (11lbs) with the 10s1p A123 reached 36000-38000rpm under load geared for slightly lesser speed than in my buggy.

It really depends on which rpm band suits your gearing options most. Expect 38000rpm with a ACn22/45/2 (1400kv) under load (depending on your gearing) with 10s1p a123, The ACn22/45/3 (1000kv) will more likely be at 28000-30000rpm with 10s1p a123 or 33500-36000 with 12s1p A123.

With 12s A123 you will have 20% more energy in your car. Due to having more wheight in your car this won't translate into 20% more runtime. But having more volts tranlates in lesser Amps to generate the same amount of power. Giving you slightly more efficiency. You might end up driving 10-15% longer with 12s. This is only a guess. I saw a jump in runtime of around 1 minute when driving with 10s1p A123 in comparision to a 9s1p setup.

What you also might consider is running an ESC at its voltage limit is always more risky then using it with a safety margin of 1-2 cells less then its rated max. So look at the specs of the HV85 or HV110 -> 8s lipo is comparable with 10s A123 from a voltage point of view. When coming fresh of a charger a123 cells are at 3.6-3.7v per cell. Droping quickly to 3,3v when used. What you also might consider is flight ESCs have a slower ramp up time when revving your motor up. Investigate on this further or you might end up with a setup which feels a little sluggish when it comes to accelerating.

On a side note the ACn22/45 series is a little heavier than a Neu 1512. Which i would consider beeing on the light side for a heavy truck. The 1512 worked well in my truggy but run hotter then my Neu 1515. More mass means more energy in heat can be stored. That is why a heavier motor is not as critical then a lighter motor. The ACn22/45 will have enough power to push your truck but i would expect it to run a little hot due to it's "small" wheight. If you're not a speed freak this will not be an issue. A heavier motor can be geared higher without breaking a sweat. But those are all estimations. Don't know if someone already tested this motor in a heavy truck.

hope this helps.

EDIT: like lutach stated. Those are continouus ratings. My average amp draw is between 15-21A when looking at a complete run. My Neu 1515/2y is rated at 50A if i'm not mistaken. I reguraly see peaks between 50-100A. But they only last for 1/10 tenth of a second under hard acceleration.

[BL_RV0]

Ok, so you're saying that a 22/45/3 is a batter choice with 12s than a 22/45/2 with 10s?
EDIT: I would like to have softer start to save my transmission and differentials.

[othello]

It really depends what gearing options you have. Crunch some numbers using BrianGs speed calculator. If you can reasonably gear a motor with 40000rpm. Go for it, but it might run hotter then a motor revving at 30000-35000rpm. If you want more runtime and lower temps go with the higher wind version. Either on 10s or 12s A123.

Wheight depends on how much does a savage roller wheigh? Wheight of your electrical components is easily calculated. Wheight of your desired tires really can make a difference in wheight. I never converted a savage, so i can't tell you.

[BL_RV0]

I've been using his calculator alot. I'll use the /3 wind, plus in some numbers, and see what it spits out.

[BL_RV0]

Here is what I got:


Differential Ratio: 3.3076923076923075
Transmission Ratio: 1.5833333333333333
Other Ratio: 0.967741935483871
Spur Tooth Count: 49
Pinion Tooth Count: 14
Total Voltage: 39.6
Motor KV: 1000
Tire Diameter (inches): 7
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor coil Ω: 0
Spur/Pinion Ratio: 3.5 : 1
Total Ratio: 17.73883 : 1
Tire Circumference (inches): 21.99 inches (558.58 mm)
Total Motor Speed: 39600 RPM
Vehicle Speed: 46.49 mph (74.68 km/h)
Effective Speed Rate: 1.17 mph/V (1.89 kmh/V)
Estimated Adjusted Speed: 44 mph (70 km/h) - 6% loss
Effective KV Value: 1000
Motor Torque: Amperage not specified...
Final Torque: Amperage not specified...
Final Power: Amperage not specified...

[othello]

You have to reduce total voltage to 32-36v (with 12s under load at full speed). A heavy truck sucks 800-1500 Watts at those speed levels (above 40mph) depending on the surface you run it. Meaning you will need up to 45A. At this amp level voltage of A123 cells drops down to 2.8v per cell.

So 33v will give you a more realistic speed and rpm under load.