Brushless Savage Setup
 

Hello folks

I am new here. Dafni told me about this great forum yesterday. As I am converting my Savage 25 RTR to Brushless I read a lot of threads here and in other (german) forums. (BTW: excuse my poor english...)

I already placed an order for a Wanderer 20XL/9 and a Warrior 12020 at BK, but I can still switch the setup as I have to wait for some parts.
After speaking with different people in Switzerland and Germany I was surprised that the 7XL is the choise of many drivers in this forum. One thing that nobody discuss here is the problem of hopups that have to be made while using a motor with so much torque... In Germany everybody tells you first about the stronger dogbones, cup joint, diffs etc. you need. Are you driving the 7XL with stock parts?? The only thing I modified is a 4-spider diff. The drive train is still stock.

Before I ask the question that everybody asks, here is my (virtual-)setup:

- BK Wanderer 20XL/9 (kv: 1667)
- BK Warrior 12020
- 16 cells GP3300 (given as I already own this)
- fixed gear
- 16/49 or 18/49

I like to build a car that is not a material-killer(!) and I drive mainly in the gravel-pit (climbing & jumping), so speed is not the one and only. I used the savage speedtable to make some calculations and I learned a lot about the sweet spot and heat regulation from Dafni. Now I think that the setup above could be optimized for my needs.

With 16 cells (calculated with 1.15 volt) I get about 30'000 rpm which is clear below the sweet spot of 35-40'000 rpm. And the speed is also poor: 24mph with 16/49 or 27mph with 18/49 translation in first gear. What can and should be changed???

a) 20XL/8 (kv:1875 -> 34500 rpm) = 27mph (16/49) / 30mph (18/49)
b) 20XL/7 (kv:2145 -> 39500 rpm) = 30mph (16/49) / 34mph (18/49)
c) 20XL/7 and fixed second gear = 38mph (14/49) / 44mph (16/49)

Is it possible to drive the c-setup (second gear)? Or does it generate to much stress to motor and drive train?
To hit the brushless sweet spot under "normal" gravel-pit condition I think the 20XL/7 is the best choice.

What do you recommend? What's the golden setup?
Serum, Mike what do you think?

-- Dave


Remember: I don't want a beast that kills all the drive train parts (the Savage will be about 15 pounds).

Hi Atilla, glad you found your way to this place.
Don't worry about poor english, the folks here are very helpful and nice.

I exchanged some mails with Serum about your setup, but that was when I still thought you were going to use 18 cells.
I wonder what the gurus will say. I would still suggest the 7XL.

Not only the motor is a part killer, but the driver too!

Hi Attila! great to see you took this time to write in English.. (it takes me some time as well, to write in German, and it's not near as good as your english..) welcome to this forum!

The savage is a tough truck! that's for sure!! I am going to do a centerdiff rebuild on a savage soon, and i will include detailed pictures why i think the savage is nice for converting to BL..

You are from Germany, so if you ever waste a diff, get the Nitro-Mods spider mod!

16 cells you could use the 9920 with the 10L or the 7XL or 8XL, using the automatic transmission. (this RULES!!!!) (be sure to get the heavy duty 2nd gear mod)

About the weight;

My allmost complete aluminum savage weighted about 14,5 pounds, with 16 cells as well..

A friend of mine runs his savage with 14-16 cells with this 10L and a schulze 18.61 with the right gearing he can peak to 71 km/h!! Brushless is really strong.

Though the 7XL or the 8XL gets my vote. With the 8XL you will be able to run it on maxx 20 cells (with the right gearing) and the 7XL will let you run it with 18 if needed..

The runtime would be about 12-15 minutes. With the XL the motor will run nice and cool

The 8XL will give you a bit more runtime than the 7XL,

Remember, the kv ranges that Lehner has with their motors is under load. With the gearing you are using

If you plan on running 2nd gear, i would use the 8XL.. (with a 16/49 gearing it is really quick (40 mph))

:C: Weird statement from myself. I wanted to say it strongly depends on HOW you drive, too. Hope you get it.

Serum: Atilla is a swissie!

Atilla: I agree with Serum. A basher truck like the Savy should be fun with the auto tranny. Why not keep both gears open?
By the way, nice Avatar. Especially the truck :p

A truck? Ahh Now i see...

With the the automatic transmission I loose the reverse gear...

Which "heavy duty 2nd gear mod" do you mean?

2nd gear fixed could be an option. But with an 8XL on 16 cells I am always below the sweet spot (~33000 rpm). Something to care about??

The more I play with the speedtable the more I like the BK 20XL/7 or maybe the BK 20L/10. The L of course draws less amps, which means longer run time. But is an "L" strong enough for a Savage???

BTW: Why does a Feigao 7XL has a kv of 2382 and a BK 20XL/7 a kv of only 2145? I thought that they are more or less identical...?

OK, when you have to choose one of these setups, which one would you prefer? (always on 16 cells and with a BK 12020 controller)

a) BK 20XL/7 (kv: 2145, about 90-95 amps)
b) BK 20L/10 (kv: 2212, about 60 amps)

Speed is for both setups nearly the same:
1st gear: 16/49= 30 mph or 18/49 = 33 mph
2nd gear: 16/49 = 42 mph

Again: is an "L" strong enough for a Savage? And does it has more torque than a stock .25 nitro Savage?

Thanks!
-- Dave

Well now. Let start with the feigo and bk motor kv. feigao does theres not under load. bk does theres under a load. Sure on paper they seem like you would get more run time out the 10L. The 7xl has more torque so it takes less power to do the same thing. You should have about the same run time. I run a 14 l right now. I had a 7xl. The 7xl had alot more power. The run time may be shorter with the 7xl. I get about 30+ min on a set of batts right now. I am not easy on a truck though. I have space and I let the truck go. I have need for speed. I would like to try a 8 and 9 xl. Just to see what they do. One guy said 25-30 min on a 9xl. He has more torque than me to. Close to same kv rating as well. but the 9xl has more draw than mine. 9 xl has about 74 will mine is only about 40. In my opinion. Go with the xl motor.

Oh yeah, I forgot. You already told me. The Oneway bearings...

OK, after reading this thread I know more about the "sweet spot" thing. Summary: every setup has it's own sweet spot.

-- Dave

Of course. But according to Mike, BL motors are most efficient around 35'000rpm.
Sweet spot and Most efficint spot are not necessarily the same. In fact they are two different things. YOu can "tune" the sweet spot by gearing, but max rpm is given by voltage. Just make sure the sweet spot is in the efficient range :)
The best is to start somewhere and observe the temps.

Let's put this sweet/efficint thing another way: The sweetspot concerns the gearing. It's an equation on gearing, weight etc.
The efficiency is a constant at a given voltage, if I understand it right.

I still don't know which motor I should take. Maybe I'll go for this one!!! :devil

Check it out!

-- Dave

Yeah, someone already posted this beast here. But I thought you don't like the nitro noise....:L:

The 10L like i said, is strong enough for a savage. A friend of mine reaches 71 km/h with the 10L on 16 cells. on 14 cells it allready is faster and stronger than a .25 (fixed in 1st gear that is)

this is the heavy duty 2nd speed i am talking about..

You don't really need a backwards, and you could use a backwards conversion for your savage.

i saw a bl savage with a 9L and a warrior for 300 bux.

If you want to stick to 16 cells, the 10L gets another vote from me.