14xl on 9s lipo?

[lincpimp]

Ok, looking for a decent HV setup for my forthcoming savage build. I have one of Mike's new forward tranny mount chassis, and a brand new ss kit coming. Was wondering if a 14xl on 9s lipo sounds good? Rpm will be slightly high, 39k, not sure if this wil cause an issue or not. I have the batteries already. They are 2500 mah 18c batteries, one 4s and one 5s pack. So I will have roughly 33v and 45amps to work with. Will 1400 watts be enough? I plan to se the stock 2 speed tranny and mech brakes, and gear for around 40mph. Just wondering if any of you HV users see any "holes" in this idea? I also have a 9xl/125b/5k 20c lipo combo that could go in this, but I would prefer to go HV if at all possible.

[othello]

Interesting project.

I suppose that 18c is their max continouus rating. You will never ever reach a 45A average discharge rate. What matters is their burst discharge ability.

When i push my 4.9Kg (10.8lbs) truggy (also geared for 40mph, 1400kv Motor, 30v average) as hard as i can (like in those videos linked in my signature) i'm able to reach 20A average at 30V (600 Watt average). On a more typical run my average is at 15A. This should not stress your battery. A savage might be slightly heavier, but you will use more voltage too.

Now if you look closer at this graph you will notice that for over 92% of my runtime the amp draw is between 0-50A. Amp peaks between 70A-110A are rarely seen (1% of my runtime). I made this graph based on the data recorded on the the same run of my linked videos. With more grip you will see more peaks above 50A but this really depends on the ability of your battery to hold it's voltage under heavier load. Those high peaks only last for 1/10th of a second. So have a look at the max burst ability of your batteries.

When holding top speed i need 800 Watt (27.5V at 30A) and the motor spins at 38500rpm. When geared for the same speed your savage might need more Watts (heavier and more air drag). Let's say around 1000 Watt -> 30A at 33V which puts your motor slightly under 40k rpm. This might be a bit high for a Feigao and will heat it up. Depends on how often you will drive it at top speed. If you look at my graph again, you will notice that 30% of my runtime i was above 30000 rpm.

My estimation is that your 14XL might be better suited for a 8s setup but this is only theory. On 9s i would watch the motor temp closer and give it a try. A even lower kv Feigao will be better suited for 9s, but i never saw a 15XL or higher.

1400 Watt for sure is enough. I also use 9s2p Konion 1100. Those are only able of 1400-1500 Watts. No more wheellies when accelerating but i do reach almost the same topspeed (they heavily drop voltage under load). Your peaks will depend on how good your lipos will hold their voltage under load (grip, driving style, and so many more factors). What lipos do want to use? You might find a discharge graph telling you their max bust rate and what voltage you can expect under load. When landing after a jump and remaining throttle i see peaks up to 2.5KW (100A@25V for 1/10 of a second).

[BL_RV0]

lincpimp- why don't you use a kb45 motor? i'm assuming you're wanting to have around 900-1000kv? check out this one-
http://www.hobbycity.com/hobbycity/s...idProduct=4935

[lincpimp]

othello:

Thanks much for the info, I have a feeling that this will work well, but the total motor speed does worry me slightly. I usually try to keep the feigao motors to about 35k rmp max. I know that my gearing will be lower to compensate for the higher motor speed, so that putas less load on the motor. Also, buy having the 2 speed there will be less load on the motor from a standing start. I have a feeling that the lipos will be fine, but I also wonder if the voltage will drop alot under load. They are efuel hobbies 18c cells that they sold a while back. Seem to be good batteries, but who knows.

bl-rvo:

I wanted to stay with a 36mm diameter motor with the std mount pattern. I am using mike's tranny forward chassis, and his motor mount is setup for the std motors. I have a few of the kb45 motors, one will actually go in my aftershock, and I have to make a custom mount for it.