MM/Feigao cogging

I've been running my truggy since I converted it and I've been having a problem with stripping spurs. At first I thought that it was due to the chassis flex; although I didn't know how this could be since my motor mount is mounted to the center diff mount.

Today, while I was playing around with the Muggy with my son driving his Monster GT (brushless of course), I nailed the throttle from a dead stop and it cogged so violently that it stripped the spur gear. I've never had that happen before, but then again, I've never nailed it from a dead stop either. I'm running with no punch control, lowest timing, and high start power.

I also have to say that I'm running way over geared. I think I'm over geared anyway. I still have the stock Muggy tires on it running 14/46 gearing, which is what I was running in my buggy, so I figure I must be over geared.

Anyway, has anyone else experienced anything like this. Could it be due to the over gearing? That's the only thing that I can figure because when I stipped the other spurs, the truck was too far away to see or hear if it was cogging.

[BrianG]

I haven't heard anyone having any trouble with 2-pole motors of any kind. Overgearing might put too much of a load on the motor and the ESC can't get the motor turning fast enough to get a rotor position. I'd also crank up the punch control and reduce start power. Even doing this, I haven't seen noticeable decrease in performance. Actually, it might help it run better since it's not working so hard. What motor (wind) was this BTW?

[crazyjr]

I get a cog every once in a while but nothing that is violent

I've never had this problem before with the MM. I don't have any problems at all with my Monster GT conversion, but that is geared very conservatively.

I suspect that the gear is just way too tall on the Muggy, so I'll have to try out a smaller pinions, when they get there.

[BrianG]

Until then, I'd try reducing the start power and turn down the punch (increase punch control) as it will be easier on the ESC...

Brian,

To make matters worse, I just got back from my LHS and all they had was a 44T spur. My order from Mike won't be in for another few days. I'm gonna run the punch control at 100%, timing on lowest, with the lowest start power setting and see what that does.

[BrianG]

Well, at least all those adjustments will let you know if you're on the right track. Changing the spur will only make it better. A side benefit to changing those settings is that you'll probably have more runtime since the batts aren't being forced to pump out so much current in bursts.

I tried all of those settings and they did help. What I'd really like to know, though, is whether over gearing can/will cause cogging? I'm asking because I didn't have any such trouble with my buggy conversion, but have had this trouble with the Muggy. All of my connections are now hard wired, except the deans going to the battery. I'm wondering if I have a cold joint someplace, but if I did, wouldn't I be having the problem all of the time rather than intermittently?

I liked all of the lowered settings, but I think that there is too much punch control. I'm going to work my way down with it, until I get to a happy medium. I'm hoping that my order of pinions gets here tomorrow. I have a 10, 12, and 14 on the way. Should I have gotten some of the odd sizes too. I just figured that going every other step should be good. Sorry for all of the elementary questions, but I'm really new to trucks and don't want to assume anything.

[Dafni]

Overgearing will definitely give you more cogging! On all ESCs, not just the MM.
Back in the BK Warrior days I used to judge my gearing by the amount of cogg I'd get at super low speeds :)

[BrianG]

While the Muggy is called a MT, it is really built like a truggy. Most MT have the spur/pinion, and tranny, and the diff to reduce ratios. From the pics of the Muggy, there is no tranny, so you lose whatever ratio there. Then, the tires are kinda big. The diameter of the tires actually has a lot to do with gearing. So basically, you have a relatively heavy truck that is geared tall. If you have a high kv motor (like a 7xl or equivalent) it may be trying to do too much with too little gear reduction. The MM should be fine at 100A, but I wonder what kind of currents you are pulling in bursts? Maybe it's too much due to the motor wind coupled with the weight/gearing of the truck?

Or, maybe your batteries are dropping voltage too much under the heavy load? Are you using NiXX or Lipos? If lipos, you can tell if it's an LVC issue by temporarily lowering or disabling the low voltage cutoff. If it operates fine, then you batt voltage is dipping below cutoff when you really gun it. And that may be a wiring, connector, and/or battery issue.

[glassdoctor]

Just a thought... I have had very severe cogging several times... but it never did any harm to the gears. The only time I have ever stripped a gear is when the motor slipped and loosened the mesh.

I don't see how cogging could strip a gear because... although it sounds bad... there really isn't much power put down. The motor does kick back and forth kinda violently sometimes but I would not think it's moving enough to do damage.

I wonder if the cogging I see on the 4 pole motors is a little different?

[BrianG]

GD: I think the Neu issue is because of the relatively high inductance of the coils since they have quite a low turn count compared to a Feigao. Or maybe the software has trouble reading the level/duration of the feedback pulses.

To me, AAngel's issue sounds more like inadequate power whether from the batteries themselves or a weak solder joint somewhere, or a matter of the ESC pulling so much current when he "guns it".

GD,

I believe that what I'm experiencing is different from what you are with the Neu motor. I believe (for what it's worth) that you are experiencing a "communitcation" problem of sorts between the motor and MM. I think that what I'm getting is a case of the motor expecting the truck to be moving and it isn't. When mine cogged that last time, violent is an understatement. I thought for sure that I had cooked my MM. It did, indeed, strip the spur upon cogging.

I'm running 4S lipo, and I don't think it's the battery. I was running a Kokam 4800 pack and it is a beast of a battery. It'll dump current at will. I wish I had some sort of data logger so that I could see what's going on. All I do know is that with the same gearing in my buggy, the problem (cogging) is almost non existent. I hope it is just that my tires are just way too big for the gearing. It must be like running a 20T pinion in a buggy.

The funny thing is that my buddy was doing the same thing (stripping spurs) with his 8ight. We had just assumed that rocks were eating the gears. We were running 16/46 gearing, but he was having more of a cogging problem than I was. He never did try a smaller pinion because he liked the performance. I wonder if his internal diff ratio was different from mine. On the track, his buggy with the 8XL running 16/46 was equally as fast an my buggy running 14/46 with the 7XL. Coming into the straight, it was really a matter of who got out of the turn first that determined who was first at the end of the straight. In know that he was running a slightly larger pinion, but I don't think that two teeth should have made his buggy that fast.

I'm hoping that it is just the gearing. I'm waiting for the postman right now. I hope he has my pinions so that I can try a 10T with the 44T spur. Better yet, I hope that my order from Mike comes in too, so that I can try the 10T pinion with the 46T spur.

If that doesn't do it, all I can assume is that I have a bad connection someplace, although I went through everything with my Fluke DMM and did not detect any measureable resistance. I do remember that when I soldered the 12 gauge wires onto this particular controller, my 700* tip for my metcal was on its last leg.

BTW, considering the size of the ground plane on this MM and its heat sinking ability, I wonder if going with an 800* tip wouldn't be better for soldering on the wires. I don't own a tip that gets that hot, but I was kind of struggling with the 700* tip.

OK, I got my pinions and spurs in. I put the 10T pinion on with a 46T spur. Just trying it out, I programmed the MM with the lowest timing setting, the lowest start power, and 50% punch control. It was much better, but it still cogged. It cogged badly enough to strip another spur gear.

I'm finding all of this pretty disconcerting. I wonder if it is just the sheer mass of the tires. Maybe it's time to just invest in a Quark/Neu combo; or maybe a Compro/Neu combo.

The thought of a cold solder joint someplace keeps popping into my mind, but I'd think that if that was it, I'd have some other symptoms manifesting themselves. Like hot wires/connectors, or something else overheating, but all is running well as long as I'm moving, or once I get moving.

[BrianG]

I'm kinda surprised really; you geared it down and lowered all the power settings and it still cogged. Did you try the idea of lowering/shutting off the LVC just in case the battery voltage is sagging and tripping the LVC? Of course you don't want to run like this all the time, but it's a troubleshooting step.

The Quark has been cog-free in both my vehicles (Hyper8 and Revo), but it costs about as much as two MM's and it's not without problems of its own. IMO it needs additional cooling, is kinda big, and it doesn't do 6s well. But it can run anything and is silky smooth.