MMM drive frequency
 

Anyone know what the drive frequencies of the MMM are? I noticed older escs such as the shulze u-force had this adjustable, and apparently, differnt motors require diffent drive frequences in order to run efficiently. Losi's exceleron has this adjustable as well. Is there a reason why the MMM or MM drive frequencies aren't be adjustable via programing?

Excellent question. I'm not CC, but I can throw in some speculation. Have you noticed how the CC car ESCs use two different drive frequencies, one to start the motor and the other to keep it going? My guess is CC doesn't have drive frequency as an option because they cater to the masses - and the large majority of the masses would have no idea what this "frequency" is - so CC left it out and stuck with a drive frequency which will suit most motors.

can you distinguish the frequency? that screeching/whining sound?

its always higher pitched at the hit of the throttle and then deepens

http://www.youtube.com/watch?v=NXQkS-BigRo

the first trigger pull you can hear it...

What exactly does the frequency do?

Here's a video I made that shows it as well:
http://video.google.com/videoplay?do...90454808&hl=en

Yeah, I notice this as well with my MM. I was looking around at the neu website and they seem to recommend 13 khz for their motors. I wonder if that is what the MMM is set at because castle will be comboing the MMM with their version neus. I would like to know for sure because there seems to be wide range of motors that people are using and each one may require a different drive frequency to run most efficiently depending on if its two pole, four pole, slotted, slottless, wye wound, delta wound, high turn, low turn or what not.

I a no engineer (at least not yet!), but I will do my best to try to explain. If patrick could chip in and correct me if im wrong that would be great.

First think of an esc as a very fast on/off switch. The drive frequency is the rate per second at which the esc turns the motor on and off. So if the drive freqency is 10,000 hertz and you are applying 50% throttle, the esc will turn on/off 10,000 times every second and stay on 50% of the time. Likewise, if 70% thottle were used, the esc would stay on for 70% of the time and stay off 30% of the time. The result of this is that the current will average some fraction of what the current would be as if full throttle were used. If you picture the graph of the current over time (assuming you maintain a certain level of partial throttle), it will look like a sine wave. The higher the frequency, the smaller and tighter the ripples, the lower the frequency, the larger and broader the ripples will be. As you might be able to imagine, higher frequency = smoother operation, but is not always better. Here is where my limited knowledge comes into play. I'm guessing that different materials including iron, which is commonly used as a stator core, have limits to the rate at which they can change their induced magnetic field. So if the drive frequency is too high, the magnetic field of an iron core will not be able to "keep up" to the changes in the magnetic field created by the surrounding wire, thus creating heat and poor efficienty. Of course at full throttle, drive frequency shouldn't matter since the esc sends power to the motor 100% of the time.

I believe (don't quote me) that Castle uses variable drive frequency on their controllers. That would help to explain the change in the audible tone generated throughout the throttle range. They DO use variable timing in their controllers, so it would kinda make sense if the drive frequency were variable as well. Both parameters being based on the load at any given time and allowing the motor to run at maximum efficiency at any load. You know, if I'm wrong about this, it may be worth looking in to. If they (CC) aren't already.

would it be able to be updated via a firmware update only? eg: i have a neu D wind, and a certain frequency is the best, would they be able to incorporate it into a firmware update, or would it require more than this.
thanks :)

13 khz

Can anyone explain why the Mamba Max would over heat with a small, but fast 6 pole motor (Mega ACn16/15/1 9200Kv) and my Hobbywing 60A didn't over heat like it. Even the Tekin R1 had heat issues with that motor. I saw in rcgroups a couple of guy who designed a high volt ESC and ran it with very high frequency with no heat issue on the motor and on the ESC.

Bump. Any input castle? Possible new feature of the castle link?

We don't allow changing the frequency on the MM or MMM simply because there are so many "novice" users who will look at the feature and assume higher is better...

Higher frequency drive is harder on the ESC, but easier on the motor. Lower frequency drive is easier on the ESC, but harder on the motor.

We chose a frequency that works well with pretty much anything from large outrunners to small slotless motors. It is a bit of a compromise, but we don't have to worry about someone pushing up the frequency to 56khz (which is the maximum PWM frequency on our Phoenix-ICE airplane controllers) and then pushing an ESC past it's maximum power. At lower frequencies, an ESC can handle overcurrent quite well -- at higher frequencies the ESC can be damaged much easier.

Our "compromise" frequency is about 12.5khz, which works very well in practically all circumstances.


Oh, and the frequency is variable during startup (part of our patented algorithm for low speed brushless motor start) and then becomes fixed at higher RPMs. During startup, frequency is dependent on motor inductance.


Lutach -- I'm surprised you saw ANY difference between the MM and any other controller on the Mega motor. Tekin uses a similar run frequency to Castle, and Hobbywing uses a lower frequency (which would usually make a motor run hotter...) Hobbywing also doesn't track back-EMF very well compared to the MM, so if anything, I would expect the Hobbywing to run the motor slightly warmer than the MM. Could there have been some odd programming (very high timing for example?) on the MM?

Is the fact that higher frequencies are harder on the ESC attributed to the losses in switching on the FETs, or the effect of motor inductance/high F on the FETs?

Switching losses are most of it.

Higher switching frequencies require higher dV/dT (and consequently, higher dI/dT) on the FETs, which is harder on the FETs.

Also, inductance effects are significantly more difficult to manage at high switching frequencies -- so wire lengths, routing, etc. all have a significant effect on ESC efficiency at high switching frequencies.

I really don't know what caused the heat issues and I tried all the settings possible at that time. Right now I'm actually running (Testing) my micro 4 pole motor with a Tekin R1 and there's no heat issues at all.

I'll be getting in toch with you so we can work on some designs I have in mind.