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Old 08-13-2008, 12:46 PM   #1
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Default Is this normal behaviour for a Mamba Max? + some BL terms Qs

Hi,

I’ve finally received my Mamba Max 5700 combo a couple days ago, and installed it in my B4. So I’m very new to the brushless world, but so far it’s just amazing! I’m loving the top speed and acceleration.

The problem is, I’m not really familiar with some of the terminology that is associated with brushless motors/ESCs, namely:

-Cogging - This is the easiest one, and I’ve already figured it out before the Mamba got here. Since it’s a sensorless system, the ESC doesn’t know where the rotor is when the vehicle is not moving, so it has to guess and it ends up sort of stuttering, or “cogging” at initial start up, especially when you apply very little throttle. At higher speeds (anything past 1 km/hr, really), this doesn’t occur of course.
-Thermalling - Ok, I can guess that this basically means the ESC overheats and to prevent damage to itself, it shuts down. But how exactly does it shut down? I want to know the specific details so I can recognize it if this happens.
-Lipo Cut Off - Again, I know what it’s for, but I don’t know how exactly it works. When your lipo gets to the specified low voltage, how exactly does it “cut off”? Does it simply lower the power output so that the lipo doesn’t sink past the cut off point, or does it completely shut down and not respond to throttle commands anymore?

I’m still waiting for my Lipo to get here, so meanwhile the only 1/10 battery I have is a 1-year-old crappy Venom 3000 NiMH 6-cell pack. I’ve heard somewhere using a weak battery can (somehow) fry your MM esc, but the LHS guy told me it’ll be fine. I'm pretty sure this pack drops its voltage to about 4-5V when under high load when its close to discharged...

Anyway, I’ve ran it a few times and everything’s pretty good so far, except one thing that happens.

Every now and then, it kinda shuts off. What is confusing me is I don’t understand the reason for it.

Here’s how it happens. It happens the most when the battery is almost fully discharged, and I give it a lot of throttle. Suddenly, the vehicle completely stops responding to throttle input. Neither gas or brakes work, so it just continues rolling and slowly comes to a stop. The steering still works without a hitch. But not throttle. In fact, when I look at the ESC LEDs, it always stays at Yellow at this point, no matter what I do on the transmitter (i.e. usually it goes green with positive throttle and red when you pull brakes, but not after this happens).

The fact that this happens more often towards the battery being fully discharged, and most often when I give too much throttle, it leads me to think it’s some sort of Lipo cut off.

The problem is, the Lipo Cut Off setting is set to “off”!

So why is it shutting down suddenly like that? And it never comes back to life after that point until I turn it off and on. Even if I leave the throttle at neutral, etc.

The only way to get it to work again is to turn it off via the power switch and then turn it on again. Usually, after the first time this happens, it will happen again very soon if I give it a little too much throttle.

My guess is the 6-cell Venom battery probably drops its voltage down to 4-5V when its at that much load. But why doesn’t the ESC start to respond to throttle input after I let go of the throttle and the battery is back to giving 6-7V at idle?

If someone can explain to me the exact definitions of Thermalling (Thermal protection?) and Lipo Cut Off and how they work in a MM ESC, so that I can identify the two events with confidence when they happen, I’d really appreciate that. So far all I know just from guessing based on reading forums about BL systems, etc.

I hope this will never happen again when I have my Lipo in place… Right?

P.S. Sorry for a long post. I suck at being concise. >.<

P.P.S. I'm using a Futaba 3PM system with the R603FF receiver if this makes a difference. It's possible the receiver itself is what is shutting down when the battery voltage drops too much, perhaps.
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Old 08-13-2008, 12:51 PM   #2
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It is shutting down because there is not enough energy in the battery to maintain good voltage under high load. The same happens with any setup, not just the sensorless brushless systems, although sensorless systems are the most sensitive out there to low voltages and low speed throttle control.

Just replace the battery.
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Old 08-13-2008, 12:56 PM   #3
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So it shuts down and doesn't restart, right?

I don't understand why it wouldn't just come back to life once I let go of the throttle.

I take it this will never happen with a decent Lipo battery then, right? I mean, I will want to stop running the car to not go past 3.0v per cell much sooner than it will shut down from low voltage like its doing with my crappy Venom 3000 now, right?

Also, is there a term for this event? Can I call it "Low voltage input permananet shut-down" protection, or is there a better name? In other words, it's neither Thermalling nor Lipo Cut Off?

Thanks!
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Old 08-13-2008, 01:38 PM   #4
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The phenomenon with NiMH/NiCd batteries lets the car restart for a moment time and time again, because the resting voltage of the cells always tries to get back to the 7.2V nominal voltage, but as soon as you open the throttle that voltage drops again, so the car will crawl a tiny bit each time you open the throttle, but all you are doing is pulling the last few bits of energy from the cells.

Best advice is to stop running the car as soon as it slows noticeably. Don't rely on cutoffs, rely on your eyes. With LiPo cells, runing the cells down too low is at worst somewhere between harmful to the cells and outright dangerous. With NiMH is is just bad for the cells.
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Old 08-13-2008, 01:42 PM   #5
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Had a friend who had the same problem you are expierencing, as soon as he popped in a Lipo, end of story.
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Old 08-13-2008, 01:44 PM   #6
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A weak battery cannot fry your ESC. Frying your ESC usually happens during over voltage (exceeding the breakdown voltage of the FETs inside) and/or thermalling...

Your cogging issue definitely sounds like a battery problem. I have a craptastic Sanyo pack that can't source high current (very low discharge rating as compared to my GP cells), and my car would stutter if I "gun" it on the throttle from neutral. It is incapable of sourcing the instantaneous current, therefore, the voltage is dipping and possibly bouncing.

Check your batteries and it connections, often times, the weak point of many power delivering systems are at the connections/connectors. Make sure that you have a good connector that is low in resistance and has a large contact surface (such as a Deans or a Duratrax Powerpoles).

Make sure that you update your ESC to the latest firmware from Castle. From some of the users that have been using the Mamba before this release in software, it makes a huge difference in the way it feels...

As for the shutdown when your batteries are discharged, it is probably an internal feature to prevent Lipos from discharging too much. There is a cut-off function built in, but there's also not letting it start back up. This is probably because all batteries can recover their voltage across its terminals, if you off-load the circuit draining it. But just because the voltage recovers, the current does not. If you allow the ESC to further drain a Lipo, even if the voltage across it recovers above the cut-off, you wouldn't want it to try to draw current again.

Do what I do, I never run my packs to near discharge, it's a bad idea for NiMH anyways, when your power starts to fade due to the battery running low, pull it off the track. At least you still have full control (throttle AND steering) when the power is fading. At full discharge, you might have the steering or none...

The reason why you have the steering even though the ESC shutsdown is probably because they are independent inside. The steering is supplied by the receiver connector, which in turn is supplied by the ESC, but the ESC does not hook up the batteries to the receiver directly. It is probably going through a low-dropout regulator since most servos does not tolerate anything over 6.0V...
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Old 08-13-2008, 01:45 PM   #7
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Ok, thanks a lot guys.

Seems like this is just a "undocumented feature" of the Mamba Max ESC, and it will not happen again, say, during a race, when I have a decent Lipo in there.

I just wanted to make sure my ESC wasn't broken or anything, as I've never heard of this type of thing happening before.

Edit: I'm still not sure how the Mamba's "Lipo Cut Off" and thermal protection features will function exactly. I guess I'll try turning on Lipo Cut Off next time and see how it reacts. But what about thermalling, will it shut off just like it does now from low voltage?
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Old 08-13-2008, 01:57 PM   #8
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The Lipo cutoff will basically cut power from the car so that your battery won't get ruined. If I remember correctly, it will put the car into a sort of limp mode. Its more of an insurance thing then anything, but don't rely on it as to when you need to re-charge the battery.

Set your cutoff to 6 volts and you'll be set.

As far as the thermaling, I think the esc will shut off completely to save from frying.
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Old 08-13-2008, 02:06 PM   #9
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Thanks for the info, yzracer.

I think this whole Mamba shutting down business goes hand in hand with how this battery's been behaving for the last couple months with my stock Tamiya Mini Cooper electronics (a TEU-101BK and a stock Tamiya silver can 27T motor).

Basically, during the first 1500-2000 mAh (out of 3000) the car was completely responsive and no problems. But after that point, I was no longer able to hit WOT from a stand-still, without the system "cogging" - Yes a 27T brushed system cogging lol). It would sort of start accelerating for half a second, then the power cuts off for a second and it slows down as if neutral throttle... as the battery recovers voltage, it would start accelerating for half a second again, etc.

When it got up to top speed, it would have enough juice to keep the car going. It would also be ok if you slowly accelerated from 0 to max speed, but not if you gunned it full throttle.

Basically, the same thing is happening here, except the Mamba Max ESC is permanently shutting down when it doesnt have enough power from the battery, and disables throttle input (basically forcing it to go into neutral all the time). Unlike the TEU-101BK, which would simply wait for the battery to recover voltage and then resume throttle operation as normal.

I wouldn't be surprised if the battery drops down to like 3-4V when its under a high load, it's in a really bad condition now lol. Maybe even lower; I wish I had a way to test its Voltage under high load. ;/

P.S. The battery only takes back only around 2500 mAh now, after I discharge it as far as I can. The last couple times it took back 2200-2300 mAh. It's really ruined by now, lol.
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Old 08-13-2008, 02:07 PM   #10
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LiPo batteries don't suffer from dramtic voltage drops as much as NiMh. I think your experiencing a voltage drop from the NiMh and the ESC is shutting down. Turn off your voltage cut-off when not using LiPo.

I had the same problem with my Ruslter - turned off the voltage cut-off and the problem went away. Just make sure you re-enable it when using LiPo.
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Old 08-13-2008, 02:12 PM   #11
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Quote:
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I think your experiencing a voltage drop from the NiMh and the ESC is shutting down. Turn off your voltage cut-off when not using LiPo.
Like I said, my Lipo Cut Off setting is "off" (which is why I was worried about this happening originally).

It seems that I'm hitting an invisible *very low* voltage cut off that you can't disable. Perhaps the battery goes down to 2V and obviously Mamba can't continue to function at that voltage, but it doesn't "re-enable" throttle operation even after the voltage level recovers.

I guess you need a really horribly ruined battery pack, like mine, in order to see this undocumented effect in action.
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Old 08-13-2008, 02:17 PM   #12
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My friend had 3 Venom 4200 NiMh packs, basically brand new, and after 5 minutes or less the car would start crapping out with each pack. He put one of my Orion 3200mah Lipo's in and can go 15 minutes+ without a single hiccup.
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Old 08-13-2008, 02:17 PM   #13
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Let me be blunt.

YOUR BATTERY IS FLAT AND KNACKERED!

This is not a "hidden" feature in the Mamba. It is not "cogging" for a brushed motor. It is not NiMH vs. LiPo. IT IS A FLAT, KNACKERED BATTERY! Replace it.
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Old 08-13-2008, 02:23 PM   #14
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Quote:
Originally Posted by yzracer758 View Post
My friend had 3 Venom 4200 NiMh packs, basically brand new, and after 5 minutes or less the car would start crapping out with each pack. He put one of my Orion 3200mah Lipo's in and can go 15 minutes+ without a single hiccup.
Yeah, Venom packs are absolutely horrible, I wouldn't recommend anyone to get them even as a first battery. I've seen the same type of feedback from many people, including myself, hehe. Its not that great initially and it gets much worse after a very small number of cycles.

---------------

Lol sosidge.

You're absolutely right.

However, it's my first RC battery. I got it a year ago and it has served me well (even if the performance it gave out was horrible) for all this time. I can't just throw it out.

Plus it's the only battery I have until the 2s 5000 mAh Lipo I've ordered gets here (should be within a week from now). I'm not gonna buy another battery right now since I'll have a great one here soon.

Well, at least now I can be sure there's nothing wrong with my ESC (at first I thought maybe it wasn't properly reacting to the changes I made via CastleLink, and the Lipo Cut Off was erroneously on, even though I set it to off; but later I saw that wasn't the case as other settings DID seem to have an effect when I changed 'em). I'm now sure it won't suddently shut down when the Lipo is here.

I think I have only one more unanswered question: what exactly is thermalling for an ESC? How does the Mamba Max ESC react when it "thermals"?
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Old 08-13-2008, 04:11 PM   #15
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Here was the answer to thermalling:

Quote:
Originally Posted by yzracer758 View Post
As far as the thermaling, I think the esc will shut off completely to save from frying.
Everything will shut off...I have thermalled my Novak, but never my Mamba.
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