Higher pinions = safer MMM's? Or no? Someone's lying.... - RC-Monster Forums

I could swore that it was determined here that the higher the pinion count on the MMM and motors used on the Flux resulted in bigger loads and more chance of frying the ESC as a result? But now HPI apparently is stating that going to the 25t vs the 20t is the safe way to keep from hurting the Castle creations MMM and motor. What?? Wasn't here that we determined the higher loads were resulted of the higher RPM as a direct result of increasing the pinion tooth count which resulted in a higher chance of MMM failure, along with voltage spikes

So....wtf. What gives Castle? Who's right, whos wrong here?

http://www.savage-central.com/module...=725986#725986

V0RT3X · 09.27.2009, 04:44 AM

Isn't that a flaw in the Flux's manual? (stating to go 25t on 6s) Guess that the HPI representative is just following the manual.

shaunjohnson · 06:15 AM

hpi and traxxas are noobs when it comes to this!!
keep it's theroetical gearing in the 40mph range and you are spot on no matter what voltage you use (4-6s....not 3s or 2s lol)

suicideneil · 09.27.2009, 08:32 AM

+1 to that.

Gearing up for speed runs is fine, but simply gearing up on higher voltage is simply incorrect- if anything you have to gear down to maintain the desired *sensible* speed (assuming you're not doign a speed run setup, hence the higher voltage).

I really would have hoped they would have corrected the manual on this issue, but hopefully someone will point out this flaw to HPI before anymore asshats try to sue them or Castle because they're too stupid to know how to look after an RTR road missile...

fastbaja5b · 09.27.2009, 09:46 PM

As they pointed out over there, almost all savage flux failures on 6s have been with the 20t pinion. Am I wrong? Show me where someone has smoked an ESC with the 25t pinion attached then.

Even the best logic in the world is flawed without raw data to back it up.

shaunjohnson · 09.28.2009, 05:37 PM

also depends on how you drive too!!

J57ltr · 09.28.2009, 06:00 PM

Quote:

Originally Posted by fastbaja5b

As they pointed out over there, almost all savage flux failures on 6s have been with the 20t pinion. Am I wrong? Show me where someone has smoked an ESC with the 25t pinion attached then.

Even the best logic in the world is flawed without raw data to back it up.

Well I can see that having a smaller pinion would cause more back EMF that has to be dissipated into the batteries and the smaller pinion could cause that. You guys use really low KV motors which develop higher back EMF (read over volt the componets) compared to a high KV motor.

Jeff

fastbaja5b · 09.28.2009, 08:54 PM

Perhaps then we are being told to run the 25t to avoid esc's frying due to back EMF. Would possibly explain the failures on 6s lipo w/ 20t pinion

shaunjohnson · 09.29.2009, 02:59 AM

only way is to test with an eagle tree hooked up methinks!

suicideneil · 09.29.2009, 11:14 AM

Yeah, something about all this doesnt sound quite right- gear down with higher voltage = dead esc? Doesnt sound right somehow; back EMF is only shunted to the caps and batts under breaking, so unless you are on & off the throttle like a jackhammer it shouldnt pose a problem...

BrianG · 09.29.2009, 11:37 AM

I think the higher back-EMF voltage/current when braking with lower gearing is stressing the TVS device until it blows and then there is no protection anymore, so those high transients are free to do all kinds of damage to the FETs (which only have a 30v rating IIRC).

J57ltr · 09.29.2009, 11:40 AM

Quote:

Originally Posted by suicideneil

Yeah, something about all this doesnt sound quite right- gear down with higher voltage = dead esc? Doesnt sound right somehow; back EMF is only shunted to the caps and batts under breaking, so unless you are on & off the throttle like a jackhammer it shouldnt pose a problem...

Exactly so running the larger pinion may not overload the ESC, but having a higher gear ratio (smaller pinion) could cause the voltage to rise above a point that could damage the ESC during braking. If you were doing a bunch of speed runs and hard on the brakes I think you could generate enough to damage it. The TVS could short and then open as they often (when they fail) do then you have little protection. I haven't tried to see how much a motor will generate at such a low KV (My lowest is 3300) but it's probably pretty high at the speed you would be braking from. Then once the componets aredamaged they could typically self destruct upon application of power.

Of course this is all speculation on my part.

Jeff

lincpimp · 09.29.2009, 11:47 AM

More load is more load, no way around that.

If the batteries can handle the addl load and draw the 25t pinion requires all should be ok. No idea on motor temps though, with the stock flux tires (which are probably out of balance to begin with) and the tall gearing on 6s lipo it will place quite a load on the flux motor.

I have not seen much raw data on what batteries were used with the cooked escs that ran 6s with the 20t pinion. Cheap batteries that cannot perform will cause all kinds issues with these high power setups, we all know that by now...

The 20t pinion on 6s should yield speeds around 50 mph. I see no reason that would cause issues. I run MMM escs on 6s lipo geared for those speeds in heavy trucks and my escs do not fry... I also use top notch batteries and know what I am doing.

Yet again I have a feeling that people who are not very knowledgeable with brushless are having the majority of the problems. These are the same people who cannot tune nitro, and most likely pay the LHS staff to replace the broken parts on their trucks... Some failures of the escs are going to happen regardless of the use, that is just how it is with electronics.

And the gearing chart in the flux manual is just that a GEARING CHART. It shows what speeds you can get with the various pinions and battery combos. I read it a while back and did not take it as a recommendation or requirement (although its existence in the manual does indicate that the listed gearing can be used).

J57ltr · 09.29.2009, 12:42 PM

Quote:

Originally Posted by lincpimp

More load is more load, no way around that.

There is a HUGE difference between Load and overvoltage. We are talking about the load, it seems the ESC is more than capable of handling that. What we are talking about is damage to the ESC through braking.

Here is where I have a problem with this. The unit is rated for, but only NOW is there ANY mention of batteries other than "We recommend A123 or other good batteries". No one knows what the specs are and there isn't any good info out there regarding this issue (except here). To me the manufacturer should have in place a way to deal with this issue regardless of the batteries used. Hell the ESC is rated for use with NimH for gosh sakes and they have a much higher resistance than any of the Lipo/Lion I have tried. You can't put this off on the customer when the manufacturer doesn't have anything on their website (until now) about any of this. The FAQ has grown a bit but when the MMM first came out there was no mention of "Hey this will happen if you use inferior batteries".

Not everybody that buys these things go to forums. It's the duty of the manufacturer to inform the public when they buy, instead of providing a pamphlet, with a little humor. Granted most people aren’t going to read it, but at least you provided it.

I work for a manufacturer and know first hand of the stupidity of some customers. I have been flown out all the way to Halifax, Nova Scotia (from Houston) for a service call because they said our system didn’t “work”, I informed them that they needed to have the scale on it’s own support stand and it needed to have X-bracing since it was 10 feet in the air. I had 7 Mechanics (I was about 23 at the time) all old timers that were very pissed with what I had to say and said I had no idea what I was talking about, and challenged me to “show me where it says that in the book” I opened it to the page on construction of the frame and all the other information pertinent. They grumbled and I explained how to build it and make sure that it was X braced. I came the next morning and there was a stand but the only supports that were knee high and about 8 feet off the ground in an H pattern. They still said they were having problems, and I could walk up grab the posts and shake the system and it would wobble for about 5 seconds. I said well you didn’t follow the instructions, an argument ensued and I asked if they had a couple 10’ sticks of Angle iron and some welding vice grips. I set one up on one side diagonally and the other on the other side diagonally in the other direction. Then tried to move it and it wouldn’t budge we started running bags and all of a sudden everything was perfect. So I know customers don’t like to read manuals, but I have been in the market for a larger ESC for a while and researched for more than a year now and there isn’t any real info out there from the manufacturer. I downloaded all the manuals, I compared and I ran into this forum.

Now I have an AAS and a very mechanical background, and I didn’t know till recently what was going on so how the heck do you blame Joe blow off the street to deal with this kind of stuff. Hell anytime I or another member on this forum are in the LHS we are the ones who get asked the questions by the staff, how messed up is that?

Jeff

lincpimp · 09.29.2009, 01:19 PM

Quote:

Originally Posted by J57ltr

There is a HUGE difference between Load and overvoltage. We are talking about the load, it seems the ESC is more than capable of handling that. What we are talking about is damage to the ESC through braking.

Ok, I understand we are talking about braking. It was my understanding that the voltage spikes that are produced during braking need to be absorbed by the battery. A battery with a high IR will not be able to absorb the voltage spikes as well, and that can lead to damage to the TVS and eventually cause the MMM to fail. I do agree that CC need to spec specific brand batteries, as that will likely be the only true cure. But the customer needs to be informend, and I always see that as the responsibility of the customer. If you do research before you buy something no one calls out the mfg for that... This is a hobby, and it is generally understood that if you want to participate you need some sort of intelligence. So expecting everything to be written down might be a bit much.

I cannot believe the heat issues that would be had using nimhs with the stock gearing on a flux, but they still say it can be done... Not the best idea if you ask me...