Curt huh? and I thought your name was Jeff..........

Wow, I didn't think this thread was bad at all. Hate to see you leave over some perceived slight, but oh well.

Taller gearing will put more load on the ESC, I'd assume that would translate into more stress on the ESC and therefore not safer for MMMs.

My Muggy weighed in around 14 pounds at one point running on 6s and geared for (including tire ballooning) 90 MPH and I ran the crap out of it for about 12 minutes and it still works to this day. That's not being used intelligently and I just had the Muggy out again earlier today and the MMM is still kicking strong, they aren't as touchy as the internet drivel leads many to believe.

EDIT: I should mention this was on 20-30C Turnigy 5AH lipos and they were around 100 degrees after the run and didn't seem to cause any issues, not all Chinese packs are bad...

If I had something to do with this, I do apologize. Now if taller gearing or lower gear ratio is desired for a pure rush of sexy Ferrari speed, then everything must be up to par and that includes the batteries used which should be also mentioned here. The lower one goes on the ratio, the hungrier (Not sure if this is an actual word :lol:) your motor will get and the ESC will have to provide the juice. The main cause of failure of a ESC is going over the AMP rating of the MOSFETs. A lot of engineers I speak with tells me a MOSFET will usually handle a little over voltage better then going above the AMP rating. Now the bigger pinion will make a vehicle go faster to a point the owner of the vehicle will have to let go of the throttle sooner letting everything take a breather or it might just be that the motor is not wasting precious energy in unloaded heat. Who knows, I'm just a noob at this brushless thing.

A little over voltage is fine but During Regen if the batteries can't handle it Its going to about 3 times the rated voltage of the FETS in which case the very thin layer of Si is damaged and the FET will short out, usually just after it's called into action again (when you take off), once one goes then the rest are sure to follow. At least that has been my experience with overvoltage and mosfets.

Jeff

Exactly. Some people don't seem to realize failures sometimes don't come from just excessive current or excessive voltage, it's a domino effect. The high voltage "punches" through and damages dialectrics. And once that is done, even if the high voltage condition goes away, high currents can flow damaging it even further, and usually much more noticeable via fire/smoke.

Of course, damage can be done just by high currents without high voltage.

That's close -- but the actual FET damage during braking is actually caused by current, not by voltage. It's an effect of voltage, but the damage is done by current.

What happens is this -- the voltage rises until the FETs avalanche -- that is, they start acting like a zener diode. On the MMM the FET avalanche voltage is around 44V-48V. When the FETs avalanche, they provide a low resistance path for current, and the instantaneous currents can be thousands of amps. This can (rarely) be high enough to damage the interconnects inside the FET itself.

We RARELY see this type of damage on an MMM though-- because the FETs on the MMM are tough enough to handle repeated avalanche currents without failing.

Much more often we see a power supply issue, where a part in one of the power supplies fails from voltage stress. We have been (and continue to) toughen up the power supplies on the MMM to help prevent these issues.

Patrick

So, in your opinion, would it be adviseable to run no more than 4s or 5s when braking is enabled in a heavier and/or highly geared vehicle? Since the rise in voltage is at least partially proportional to the supply, this would give a little more leeway before the avalanche occurs. Or how about offering a TVS/capacitor board module so people with more aggressive setups can add something for a little more protection against ripple and braking?

And by power supplies are you talking about the drivers for the fets or the BEC, or something else?

Thanks,

Jeff

No, I'd suggest running BIG, high quality batteries. The best way to prevent voltage rise on the bus is to have low impedance batteries.

Lowering the voltage is an option, but the batteries are more important -- insufficient batteries will cause high voltage rise on the line even with lower voltages.

Thanx!

No, I'm talking about the power supplies themselves. There are three on the MMM -- one for the processor (3.3V), one for the FET drivers (12V), and one for the BEC (6V).

Ok kinda what I thought.

Now on the large pinion smaller pinion issue is it safe to say that having a numerically higher gear ratio will cause more back emf which could exacerbate the problem if the batteries are sub par?

Thanks again,


Jeff

In 99% of the cases, that is exactly true. Smaller pinion = less ESC stress.

Lol! By numerically higher I meant using the smaller pinion could cause a problem on subpar batteries due to the motor spinning faster from the start of braking.

Jeff

Which brings us back to the original question in the thread title. See Freezebyte, we get to the answer eventually. :smile:

Patrick, I edited an earlier post apparently after you responded. Any ideas on offering a TVS/capacitor module one could solder to the MMM power wires (not to the PCB)? Definitely not a replacement for good quaility batteries, but would provide some peace of mind.

Pretty good idea. I'll look into it. :yes:

I think your missing the point on the cheap batteries. The point is, they don't screen out the bad cells so you could buy 3 of those packs & have 2 of them work fine but the 3rd one might have a higher resistance cell. It could cause a bunch of ripple to esc & kill it.

So your right, not all Chinese packs are bad but you will never know if your buying the "bad one" or not. The brand name companies (that charge more) are taking the time to test & screen out the bad cells & NOT assembling them into the packs they will sell. That's what your paying for.

Ha, so lower gearing is better for the esc- now theres a revelation :lol: I didnt believe for a second that using higher gearing was better for the esc on any given voltage, as was suggested earlier.

I never got an answer to this. Please?

Patricks answer is exactly the opposite of what I asked though.

As far as an external circuit, I am making a clipper circuit that uses a fet that is driven by a Zener in series with a resistor. Once the voltage rises above about 30V it drives the fet on and the load is dumped into a 10 ohm 5 watt resistor (Think I am going to go to a 10 watt though). This is specifically for the motor I use, but I am sure it could be applied in this case as well.

Jeff

Also higher and lower gearing means different things to different people. Higher gearing may mean higher speed (numerically lower) and lower gearing may mean Lower speed (numerically higher).

To me Higher gearing means Numerically low (or shorter gearing) and lower gearing means numerically high (or taller gearing)

That just confuses people saying things like numerically higher or lower; why not just say taller gearing or lower gearing, as in gearing up and gearing down, or using a larger pinion or smaller pinion. Plain english = less confusion ( to me atleast, bunch of geeks :na: ).

Well I am used to 1:1 cars so I use the terminology that is associated with them. You guys confuse me when you say “I’m running 87/17 in an XYZ”. To me that means nothing other than the ratio between the spur and pinion is 5.12:1 but it leaves out the rest of the gear reduction like the transmission or differential gearing. Like in a rock crawler where you might have a 3:1, in the diff a 5.12:1 for pinion and spur and a 2.72 for the transmission, which would be an overall ratio of 41.78:1. You RC guys are weird I guess.:tongue:

Jeff

That's because for a specific vehicle, the tranny and diffs are constant, so only the spur/pinion need to be specified. If someone does do some custom tranny or diff work, then they specify. We're not weird, just lazy and don't want to type what we don't have to. :smile:

Brian - Effectively that is what the Novak Transcap does if i'm not mistaken...

http://www.shopatron.com/products/pr...ber=5685/135.0

Description

This is a Power Trans-Cap Module for use in high-voltage applications with an input voltage range from 4S to 6S Li-Po. This module includes an 1,800µF power capacitor rated at 35V and includes two transorbs to reduce ESC temperatures and provide protection for the ESC. This module is factory wired with 4 inches of red and black 16-gauge silicone wire, and solders directly to the ESC’s positive and negative battery solder tabs. Module is rated for use with 4-6S Li-Po packs. Exceeding this input voltage will damage the module.

So they gear like Ford then? :lol:

Jeff

I'm not Brian, but that's what it is and what he was talking about earlier. The cap is there to smooth ripple and the TVS's clamp down on the voltage to a safe level.

Jeff

I kinda built my own. I use 2 to 3 caps and two tvs. Single caps still blow a leg off at times.

Kinda's ass you built one!

Jeff

Yes, just like that, except turn that single 1800uF cap into 2 or 3 smaller uF caps for better heat dissipation, use 12-13GA wire, and maybe have 3 or 4 TVS devices. Basically beefier for the higher powered setups. Also, it would be nice if Castle had their own to go with their products.

Besides, on the Novak version, $18 is a little steep for 3 cheap devices IMO. That probably can be assembled for under $5, and that's not even counting bulk ordering.

You forgot that the 18bucks covers marketing, packaging and what not. Not everybody is capable of building one, less where to begin. For those people 18 bucks is a bargain.

I suppose, but it's really no more difficult than wiring up battery connectors and wiring.

You'll be amazed at how many people are incapable of doing such a thing.

And judging by the bad solder jobs I see on here I would say that most would be better off buying the premade items.

For the BEC I am building it cost me $7 for 20 TVS's shipped, Didn't have to pay for the fuses since I needed them for a work project. Gotta love Swiss Navy Projects.

Jeff

Wow, Novak. I should start having them made with either 2 or 4 small caps (The last one would make Novak's knee buckle and wouldn't be near what Novak charges).

http://i260.photobucket.com/albums/i...h/DSC01855.jpg
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Lutach,

those with the 4 caps are still my Fav.

Good lord, whats with all the caps? And about my earlier post, it was about something else which im over now so just nevermind me :whistle:

bah, stupid DP

So we STILL haven't gotten a conclusive answer in regards to weather higher gearing with larger pinions = death to ESC's

Here is a quote from this thread made by the owner of Castle Creations (Patrick):

In 99% of the cases, that is exactly true. Smaller pinion = less ESC stress.

Not sure how much more conclusive of an answer you are looking for here? 99% is pretty conclusive in my book. :)

I asked if having a smaller pinion could cause more back EMF that could cause a failure if the batteries are up to the task, to which the asnwer was

So basically to me he is saying that in 99% of cases having the smaller pinion can cause this problem with the regen braking. But he ends with the statement of smaller equals less stress.

Those two statments given that Patrick are opposed to one and other unless he meant 2 different things.

Small pinion+bad batteries= damaged ESC

And Small pinion= less stress on the ESC under load.

Or he missunderstood higher numerical ratio.


Conclusive answer?:neutral: