An idea for a new MMM or MM feature for Castle
 

Since the controllers are software based I was wondering how difficult it would be to add a max voltage out feature to the motor.

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.

This would allow someone to buy a single set of 3S batteries and then be able to use them in any application. Originally I thought about a transformer between the battery and the esc to get this done, but I have researched and for these currents it seems that it would be too bulky to want to fit in an RC truck.

Ayone have any thoughts. It seems that this would be a very easy software change for the controller. It would also help with the new E-Revo as you could buy a set of 3S batts and when someone is driving it that doesnt know, it would be toned down.

It would be similar to Traxxas's 50% reduction feature they have on their ESC, but much more advanced.

Great concept. but with lipo's and BL voltage usually isnt the problem- its usually amp draw. now THAT would be pretty neat to limit the maximum amp load so that it doesnt over-amp your batter.

Hey Guys,

Here's an idea. I know this method doesn't give you voltage number settings, BUT...........

Couldn't you just go into the Throttle curve page. On the upper end of the scale, limit full throttle to a set percentage of what "full" throttle used to be?

You don't have to flat line the throttle curve at the top, just make it peak at say hmmmm........

14.8 volts divided by 22.2 volts = 66 percent.

This isn't going to limit amp draw IMO, but it will limit the maximum volts that will be sent to the motor.

I hope this helps. :yes:

Punch control will limit your amp draw from the battery. I will play around with the throttle curves. I have never played around with them, but if it will do that then I think that it would work.

The way I understand Punch control:

Punch Control only limits Amp Draw for the first few seconds of startup. It will allow full power, but how far you turn it up determines how long it delays before it allows full power.

What you guys are looking for is current limiting, otherwise known as torque control. We've been asking CC for this for a while, but no luck as of yet.

Limiting the voltage isn't a good idea - ESCs are most efficient at full throttle (voltage).

When the esc is not operating a full throttle the fets are still switching, and that produces the heat. I guess the thermal design of the MMM with the temp controled fan may be able to cope with this... Not sure if it is a good idea as it will most likely wear the fets out faster...

Oh yeah, doesn't adjusting the throttle epa do what your asking. Set the esc up with the epa at 100% and then just dial it back to 66% or whatever. Still going that have the heat issue...

I know with my E Revo/Medusa setup, the majority of the time is spent well below full throttle. :lol:

On 6S, full throttle means "out of control" alot of times. Well, maybe from a 30mph punch. :lol: :yes:

Sikeston34M,
You are correct about punch control. Its only at startup that we have the huge inrush currents. My setup is 35 continuous and 78 peak. I think Brushlessboy is trying to eliminate the startup peaks to save his batteries. If he is talking about continuous currents and limiting those then thats something else and I missed the point.

Thats a good point Linc about the heat, which is why I was thinking about a transformer setup before you hit the esc before this idea. But running the motor at 6S has its advantages too of less heat etc etc. Never played with throttle EPA but ya I would be worried about the heat issue too. Some guy did that on the traxxas forums with 6S and 7xl and smoked an MMM (not BEC issue).

Good point too Sikeston34m, I'm not sure how many people are going to be running at WOT all the time or if you even can.

Well 6s on a 7xl just spells stupidity... i managed to kill two 8xl' rotors on 5s...

Motor probably blew then pulled the esc down with it.


I run wot when all four wheels are on the ground. lol

I have always thought about getting an 8xl on 5S. RPMs are not that much more than a 7XL on 4S and I thought it might run cooler. Looks like 35k rpm really is max for those motors.

9XL on 5s is scary, and thats with rather modest gearing :whistle:

But yeah, keeping the rpms below a max of about 40k is imperitive to keep the motor happy, and in one piece...

1515 1y on 5s is even worse :lol:

or 1515 1Y on 6S :lol::rofl:

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).

try the 1.5d on 5cell :gasp:

Exactly... Thats been around for years.

i run this motor on 6 cell an wowowo to fast:gasp:never pass 155f on 14/68

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

Pretty sure MGMs do this. I ran 18 cells NiMH in my E-Revo and they were only warm at the end of the run, but it had no performance. With my Maxamps cells it backs off the power and has been able to feed my 1515 1.5D in my Muggy without blowing any cells. With my 5s Zippy-H pack it has never backed down though :yipi:

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.

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?

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.

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?

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.

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?? :surprised:

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

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).

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

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". :smile: IIRC, the SR has to do more with the gate capacitance.

Ahh, ok. Forgot that one.... :slap: :mdr: But woudn't a higher value of Idt be indictive of a high SR?

other good feature for the mmm to add....a Motor blocked protection:yes: or a feature for the esc will be able to detect that the motor have a problem like a bad pluging , wire shorted or a to hot motor at this time the esc detect the lost of magnetic property of the rotor...and shut down the esc ..at this time we will be able to know that the motor is the problem,just add led flashing code saying that...(i hope im clear!!loll)


and a option to activate the fan by the software(always spinning),,,,could it be a good thing when running in really wooot condition