:party:

So Fat kid Joe's problem was the servo? He said he added a cap to the reciever and the problem went away, his Beta version didn't show the same problem and 2 other people have the same problem he had. He (I guess) put the MMP into another car and doesn't have the problem (I guess with a different servo)?

Jeff

I think I'm one of the "other 2 people" that you're referring to......

The problem I was having was definately a messed up servo and had nothing to do with the ESC.

Since replacing the servo, the ESC performs GREAT! :yes:

It's in a Rustler now on 5S. It's alot of power and the esc doesn't seem to mind at all. :yes:

Way to go Castle! I think you hit the ball out of the park on this one.

yes i still run the cap , it helps alot it wont shut off anymore :)

So Joe, have you checked out your servo?

sikeston34m, Yes you and Joe's friend are the other 2 I was refering to. What was wrong with your servo?

Jeff

I believe it was a factory defect. I took the servo apart and it's control board was burnt.

This tells me that I "over amped" the BEC inside the MM Pro, without damaging it.

I also believe the BEC has over amp protection.

As a servo's gears begin to wear, it draws more current. If a person is having problems like this, my advice would be to check your servo.

So it was a new or pretty new servo in your case? I am wondering why adding a cap "fixed" Joe's problem.

Jeff

WARNING: Long boring technical explanation follows: :sleep:

We've seen the same thing on the bench since this problem was reported. Apparently, some of the JR servos draw peaks (short -term) of several (5-6) amps for a couple milliseconds when changing direction. (We have speculated that the drive transistors in the servo are shooting-through during direction changes, but haven't yet verified that.) It's just barely long enough of a surge to trip the BEC over-current protection in the MMPro, and it shuts off the BEC for about 50ms. Adding a big capacitor to a servo connector (like a stutter-stopper) supplies enough current during those big surges to keep the MMPro from tripping the over-current on the BEC.

We are bench testing a hardware change that will add a very slight delay to the over-current shutdown on the MMPro to compensate for the JR servos.

Note that we have only seen this behavior on two specific JR servos, and adding some capacitance to the BEC line seems to be a good fix for the issue.

Patrick

Thats why I love this forum and CC, where else and what other manufacturers would talk as openly and get as detailed technically as Patrick and crew do here. You guys rock!

No such thing as a long boring technical explanation. Thanks for the info.

So could the same thing be happening on the hitec servo as well? What is the minimum amount of capacitance you would recommend?

Thanks

Jeff

Cool info Patrick. I wonder what causes this current "shoot through"? Could it be a timing issue with the H-bridge on the servo driver circuit? I suppose it doesn't matter since there is little that can be done short of getting a new servo. I just hope adding a delay doesn't mask a true problem because repeated current bursts from a legitimate condition could overheat the BEC and eventually cause a true failure. The BEC looks like it has foldback current limiting, so that's good. Adding a simple capacitor to an unused servo port on the receiver is an easy and cheap solution IMO. Anything between 1000uF and 4700uF @ 10v rating should be sufficient. Any higher capacitance may actually trip the BEC's overcurrent protection when the cap intitially charges. And even though the BEC output is virtually noise-free from the MMPros I've looked at, a cap would also filter any noise which some receivers are sensitive to.

The same thing could happen to any servo really. Or, it could happen if a servo stalled because of radio EPA set too high, simply a faulty servo.

yea i tryed it on my old hitec 5955tg and it did it , i got a brand new 7955tg and still did it , so it was not a bad servo , but looks like you guys are on your way to fixing it :) for now ill just run the cap

Hello,
I have the same problem with a SAVOX SC-1258tg and I have to had a capacitor on my Spektrum receiver.

No more problem with the Capacitor

So basically if you're running a large servo, put in a glitch buster capacitor and you're fine.

Had no issues with mine on 4s in the Slash with a Futaba S3050 servo. ESC didn't even get warm running a 17.5 motor. (But my highest amp spike from the motor was a whole 64 Amps lol!)

I run a JR DS8711 in my Muggy with the MMM (same BEC as the MMP, according to Patrick) which puts out over 400 oz/in. of torque and the MMM's BEC handles it perfectly. I personally don't think there's anything wrong with their BEC.