An idea for a new MMM or MM feature for Castle

[hemiblas]

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.

[brushlessboy16]

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.

[sikeston34m]

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.

[hemiblas]

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.

[sikeston34m]

Originally Posted by hemiblas

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.

[MetalMan]

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).

[lincpimp]

Originally Posted by MetalMan

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...

[sikeston34m]

Originally Posted by MetalMan

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).

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

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

[hemiblas]

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.

[brushlessboy16]

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

[hemiblas]

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.

[suicideneil]

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

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

[brushlessboy16]

1515 1y on 5s is even worse

[George16]

or 1515 1Y on 6S

[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).