An idea for a new MMM or MM feature for Castle

[Semi Pro]

Originally Posted by George16

or 1515 1Y on 6S

try the 1.5d on 5cell

[e-mike]

Originally Posted by Semi Pro

try the 1.5d on 5cell

i run this motor on 6 cell an wowowo to fastnever pass 155f on 14/68

and for the feature i would like to deasable the BEEEEEPPP song...and the auto timing mode...

[BrianG]

Originally Posted by hemiblas

...Idea: Lets say you have only 6S battery config but you only need 14.8V because 22.2V out. It would be nice to program the controller with a max voltage out setting to run the motor within spec. Or maybe a percentage of battery output feature that would limit the voltage of the battery to the motor.

There are only two ways to limit the voltage to the motor:

1) Through chopping off the excess voltage. This is known as linear regulation and is extremely inefficient because the excess voltage X current flow = power needed to be dissipated on the FET. So, if you drop the voltage from 6s to say 4s, that's a 7.4v drop. At even a low 20A, that's 148w! So that's out.

2) Through PWM. This involves sending narrower pulses to the motor. So, if you send 6s pulses (22.2v) at 10% duty cycle ("DC"), the motor is seeing an average voltage of 2.22v. 50% DC = 11.1v, and so on. This is what gives you efficient variable speed capability. The trouble with limiting the DC, as others have noted, is that everything runs better at full voltage. So, despite the somewhat less efficiency of limited DC, this would be the only practical option.

So, to get what you want, it would just be a matter of setting your throttle EPA to something less than 100%. Or, you could use programming on the ESC instead, but it's just easier to use the radio (and allows you to change on the fly).

[jhautz]

Originally Posted by BrianG

So, to get what you want, it would just be a matter of setting your throttle EPA to something less than 100%.

Exactly... Thats been around for years.

[hemiblas]

Originally Posted by BrianG

There are only two ways to limit the voltage to the motor:

1) Through chopping off the excess voltage. This is known as linear regulation and is extremely inefficient because the excess voltage X current flow = power needed to be dissipated on the FET. So, if you drop the voltage from 6s to say 4s, that's a 7.4v drop. At even a low 20A, that's 148w! So that's out.

2) Through PWM. This involves sending narrower pulses to the motor. So, if you send 6s pulses (22.2v) at 10% duty cycle ("DC"), the motor is seeing an average voltage of 2.22v. 50% DC = 11.1v, and so on. This is what gives you efficient variable speed capability. The trouble with limiting the DC, as others have noted, is that everything runs better at full voltage. So, despite the somewhat less efficiency of limited DC, this would be the only practical option.

So, to get what you want, it would just be a matter of setting your throttle EPA to something less than 100%. Or, you could use programming on the ESC instead, but it's just easier to use the radio (and allows you to change on the fly).

Thanks for the technical response. Are you a sparkie in real life? I am but just dont get into this part of it. I do realize that these things run better at full voltage, but thats about 50mph on everyones vehicles. I would assume less then 5 percent of someones run is always at full voltage. There just isnt enough street or track to keep them at WOT all the time. So sounds like it would be a simple programming change for the controller, but chaning epa on radio might be easier. I have never played with that feature, I guess I need to look.

What about an extrenal transformer between the batts and the controller? Maybe something like the Castle BEC with variable voltage output, but on a much greater scale? SAy 200A of handling power instead of 4A

This would be a great feature for the new E-revo as a user could dial his power output based on experience. I highly doubt the new traxxas 2.4 gig radio is going to have an epa setting.

[BrianG]

I don't they could void a warranty for running at a limited EPA. After all, doing that is like running with the trigger not fully engaged. And they don't say not to run slower speeds, just that it's not efficient to do that all the time.

Originally Posted by hemiblas

...What about an extrenal transformer between the batts and the controller? Maybe something like the Castle BEC with variable voltage output, but on a much greater scale? SAy 200A of handling power instead of 4A...

Not likely. A transformer needs AC to work, so you'd need a switching circuit, and then the sheer size to handle those levels of current would be prohibitive. The end result would be far larger/heavier than the ESC itself. At that point, it would be easier, more efficient, and cheaper just to get the ideal battery or motor you need.

I understand all this, and the limits set up in the radio are fine, but setting an ABSOLUTE LIMIT to Duty Cycle - enforced in firmware - would reduce the possibility that the receiver (or, in my case, robotic brain) would send the model, uncontrolled, in to a concrete wall.

Because, if the MMM glitches out, chances are the model will just freeze. If my robot controller glitches out, then there is a GOOD possibility that the model WILL fly.

A PWM Duty Cycle limit would be very useful for me, efficiency be dammed.

Not to mention, if you have kids and you want them to try out your pimp ride, wouldn't it be nice to just limit the high end to kid safe speeds?

Originally Posted by BrianG

There are only two ways to limit the voltage to the motor:

1) Through chopping off the excess voltage. This is known as linear regulation and is extremely inefficient because the excess voltage X current flow = power needed to be dissipated on the FET. So, if you drop the voltage from 6s to say 4s, that's a 7.4v drop. At even a low 20A, that's 148w! So that's out.

2) Through PWM. This involves sending narrower pulses to the motor. So, if you send 6s pulses (22.2v) at 10% duty cycle ("DC"), the motor is seeing an average voltage of 2.22v. 50% DC = 11.1v, and so on. This is what gives you efficient variable speed capability. The trouble with limiting the DC, as others have noted, is that everything runs better at full voltage. So, despite the somewhat less efficiency of limited DC, this would be the only practical option.

So, to get what you want, it would just be a matter of setting your throttle EPA to something less than 100%. Or, you could use programming on the ESC instead, but it's just easier to use the radio (and allows you to change on the fly).

[kulangflow]

From the CC FAQ:

1. I bought the Monster Max system and it's way too fast! How do I "tone it down"?

Answer 1: Lowest timing advance, smallest pinion and largest spur gear, and experiment with punch control. Always do these three things FIRST. It's not a good thing to dial down the top throttle endpoint, especially when you can re-gear, or just go down in cell count. The batts, the ESC and the motor will all run hotter than normal in a system with turned down endpoints to slow it down. The ESC is thermally protected, but the batts and motor are NOT.

Answer 2: We're working on RPM limiting, and some other software to soften the extreme nature of the system until the users get used to controlling this much power.

Answer 3: If you owned a Ferrari, would you have to drive it full throttle through your neighborhood? The system is not uncontrollable; your finger just needs time to learn how to control the throttle trigger on a high power setup.

Answer 4: We also have more great tips for slowing the systems down, and generally tuning them to your preference in our Monster Max tuning guide.

Answer 5: Drop down to a lower voltage, or install a lower kv motor.

So, they are suggesting you don't use the EPA to tone it down. Is there any chance it would affect the warranty if you did?

[What's_nitro?]

What we need is (basically) an adjustable, compound PWM output to the motor. The three-phase pulses themselves being the carrier PWM signal, then each individual pulse made from its own PWM signal. That is how you would control maximum motor current during the entire run.

[BrianG]

So are you saying the existing pulses would be further chopped? Isn't that the same as simply increasing the frequency of the pulses to get a finer resolution? Motor inductance would become an issue I would think...

[What's_nitro?]

Originally Posted by BrianG

So are you saying the existing pulses would be further chopped? Isn't that the same as simply increasing the frequency of the pulses to get a finer resolution? Motor inductance would become an issue I would think...

In this case, increased pulse frequency would equate to higher motor speed since it is the primary motor pulse that would be modified.

This method would put a MUCH larger strain on the FETs since as the carrier pulse increases in frequency as motor speed increases, the carried pulses would need to increase in frequency as well to maintain the set duty cycle at a resolution suitable enough not to affect the efficiency of the system.

......Did I just say that??

[What's_nitro?]

Yeah, motor inductance might be a problem since those carried pulses would need to run almost into the MHz range at higher motor speeds.

[BrianG]

But I think efficiency would fall. Not only would you probably get into a frequency the motor inductance wouldn't "like", but you are increasing the on-off cycles, which multiplies slew-rate losses (the v-drop while the voltage ramps up/down).

[What's_nitro?]

Wouldn't the MMM "superFETs" have fewer of these slew-rate losses due to the very small (comparably) Rdson and Idt values?

[BrianG]

Those two values really have nothing to do with slew rate. Slew rate is how quickly the voltage can change over time. Obviously, higher is better - looks more like a square-wave instead of a "trapezoid-wave". IIRC, the SR has to do more with the gate capacitance.