4s Power???

[mikro383]

I need some help from somebody who has or is running a LCC on 4s lipo's. I've got a Castle Creations Mamba Max Pro internal bec set at 6v, Tekin Redline 17.5t, 12t pinion CC bec straight to my servo, hitec micro dig servo, running 3s with no fan, v3 cvd's and fmj mods overdrive front. Am i looking at disaster or should i just run a new Tekin ROC what kv rating want more power overall.

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[losikid]

Get the 3000kv+ roc, and keep ur 3s...i'm running a 13.5t redline on 3s, and its awesome, but the low end doesn't seem very smooth when bound up, i think just the lack of low end torque, which will shine with a roc...I'd have a roc right now, but i'm waiting on holmes and a stubby outrunner to drop me an easy 3oz out of the chassis.

Did i ever send you your stuff?

[mikro383]

Yes thank you, it took some creativity to make my servo fit, had to space it out a ways because it got into the shock bad, the low end in binds is what I'm really looking for

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[losikid]

It should of only got into the spring...which isn't a huge a deal, i'm running big bore shocks and its into my springs, i'm also running the servo alot lower too

[losikid]

I'd say get the roc, because you'll have heat issues get worse with a 4s...and the 3000+kv one will give you plenty of umph, you'll probably be able todo wheelies with your losi.

Also, your low end smoothness will decrease with more voltage

[Olle P]

Originally Posted by losikid

Also, your low end smoothness will decrease with more voltage

This part I don't understand. Feeding the motor 1.5V or so should be the same no matter if the battery is at 6V or 16V, right?
(Adjusting the throttle curve should help providing precise control at the low end too.)

[WAM]

I recently installed a ROC 2300 and have initial mixed results. It's a good blend of torque and power, but it judders at minimum speed crawling down maximum downslopes. The tires move about 1/4" at the lugs then stop...and repeat. The juddering is enough to reduce my max downhill angle compared to brushed smoothness. There's still work to be done, and Tekin is looking into it with me. This with a MMP & 3S, LNC tranny and 16/18/20 pinions so far. And I've tried all expo settings, and various esc throttle curves, neither of which affected the pulsing.

[mikro383]

Good info guys, WAM are you running a external bec? It maybe the problem, and I've also read to run in sensored mode not smart sense

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[mrG]

I've been running 4s for 2+ seasons now with no issues and its as smooth as can be. I have a redline 21.5 with 14mm rotor and a 12t pinion and will never change it. Tons of torque and to get the wheels speed I want I dial up the CHEAT timing on the mmp. I set it to come in at the last 1/4 or so of the throttle travel.

[mrG]

Are you running the HD worms?

[mikro383]

Was now just front no testing yet

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[losikid]

Originally Posted by Olle P

This part I don't understand. Feeding the motor 1.5V or so should be the same no matter if the battery is at 6V or 16V, right?
(Adjusting the throttle curve should help providing precise control at the low end too.)

The esc doesn't feed it 1.5 volts at low speed, what it does is feeds it the full battery voltage and rapidly turns the power on and off, for slower speeds it does short bursts, for faster speeds it does longer bursts.

So when you up the voltage, you're decreasing your low end smoothness because its still seeing the full 16v for ex, just abunch of rapid, short bursts of it. Which will create more torque vs a smaller voltage battery, and would need a greater load on the motor to smooth it out at low speeds

[losikid]

Originally Posted by WAM

I recently installed a ROC 2300 and have initial mixed results. It's a good blend of torque and power, but it judders at minimum speed crawling down maximum downslopes. The tires move about 1/4" at the lugs then stop...and repeat. The juddering is enough to reduce my max downhill angle compared to brushed smoothness. There's still work to be done, and Tekin is looking into it with me. This with a MMP & 3S, LNC tranny and 16/18/20 pinions so far. And I've tried all expo settings, and various esc throttle curves, neither of which affected the pulsing.

Thats how my 13.5t redline is...Did you try the current limiter like the tekin guys said in the roc thread...it'll not allow so much torque to build up at the very slow speeds so it'll smooth it out

[Olle P]

Originally Posted by losikid

The esc doesn't feed it 1.5 volts at low speed, what it does is feeds it the full battery voltage and rapidly turns the power on and off, for slower speeds it does short bursts, for faster speeds it does longer bursts.

It doesn't do "bursts", but use PWM that's a simple high frequency square wave output with the desired target voltage as the average (RMS).

Originally Posted by losikid

So when you up the voltage, you're decreasing your low end smoothness because its still seeing the full 16v for ex, just abunch of rapid, short bursts of it. Which will create more torque vs a smaller voltage battery, and would need a greater load on the motor to smooth it out at low speeds

The PWM frequency is so high that the motor's mechanical inertia should be more than sufficient to make it "smooth". (With considerably less than 0.1 ms between each "push" it's not something I'd notice as a driver.)

[Olle P]

Originally Posted by losikid

The esc doesn't feed it 1.5 volts at low speed, what it does is feeds it the full battery voltage and rapidly turns the power on and off, for slower speeds it does short bursts, for faster speeds it does longer bursts.

It doesn't do "bursts", but use PWM that's a simple high frequency square wave output with the desired target voltage as the average (RMS).

Originally Posted by losikid

So when you up the voltage, you're decreasing your low end smoothness because its still seeing the full 16v for ex, just abunch of rapid, short bursts of it. Which will create more torque vs a smaller voltage battery, and would need a greater load on the motor to smooth it out at low speeds

The PWM frequency is so high that the motor's mechanical inertia should be more than sufficient to make it "smooth". (With considerably less than 0.1 ms between each "push" it's not something I'd notice as a driver.)

[Hardline]

Originally Posted by Olle P

The PWM frequency is so high that the motor's mechanical inertia should be more than sufficient to make it "smooth". (With considerably less than 0.1 ms between each "push" it's not something I'd notice as a driver.)

Don't know about that. Need to see an O-scope trace to believe that number. But I agree that the observed tire pulsing is unlikely to match the PWM frequency. I'd guess it has more to do with magnet spacing, number of slots or poles or something like that. And the resistance of the worms causing a "bounce back" effect.

[crashinaz]

I was about to buy one when they were released, but the packaging with an 18.5mm rotor concerned me. I'm guessing air gap closed a bit in the process of making room for it (which would also help the torque cause, but MAYBE make it a little notchy). I'm curious to see what they find.

[Olle P]

Originally Posted by Hardline

Don't know about that. Need to see an O-scope trace to believe that [0.1 ms] number.

That's just from reasoning:
- If the frequency is in the audible range (20 Hz to 20 kHz) you'd hear the motor all the time, just like the "tones" given off by it while the ESC is starting up.
- Below audible range the PWM would be below the motor speed, which just won't work.
- Therefore the PWM frequency needs to be >20 kHz (period time <0.05 ms).

[D_Frawg]

Pulse Width Modulation is exactly that; pulses of a square wave the width of the wave depends on the amount Root Mean Square Voltage the wave looks like to the motor (and the fact that its divided between two of the three wires to pull the magnet around in a circle(3 phase)) but so fast you cannot notice it without a o'scope. Your motor can only use so many watts(shown on novaks spreadsheet) if you up the voltage you need less amperage to do the same amount of work(watts) hats why a 7.4v lipo gets hot and a 14.8-18.4v lipo powered motor gets hot.

I run 4s mmp13.5T 20T in myLNC And 4-6s mmp 10.5T 14T LCC with no heat issues plenty of speed to put either one on its back / smooth as butter on the bottom end and enough torque To snap axle pins like nobody's business.

Chugging downhill is the nature of the worms stay on the throttle if you don't want Tourette's on the downhill.

[WAM]

Originally Posted by D_Frawg

Chugging downhill is the nature of the worms stay on the throttle if you don't want Tourette's on the downhill.

I run against two LNC sportys that are butter smooth creeping down hills at near zero speed. But they're both on brushed motors.

Maybe it's accurate to say chugging downhill is the nature of worms with brushless...dunno. I hope (and expect) there are ways to get around it.