Higher pinions = safer MMM's? Or no? Someone's lying....
 

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?:neutral:

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

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.

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)

+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...

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.

also depends on how you drive too!!

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

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

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

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... :neutral:

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).

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

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).

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

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...

Jeff,

You have to realize what we (as a company) are up against. There are battery manufacturers that sell batteries we would rate at 15C, but they label them as 35C. And then there are other companies who sell batteries that would easily rate 40C, but they label them as 30C. And there are companies that sell 30C cells that should be rated 15C, and 35C cells that are just reasonably rated.

So how are we, as a company, supposed to inform the customers? If we tell them "Don't use brand A, because they lie about their ratings" and we have a lawsuit (and yes, we can be sued by a company based in Hong Kong, but we can't sue them...) If we tell them, "Use brand B, because they are good quality" and we have OEMs who sell their own batteries at our throats. If we tell people how to determine if their batteries are good quality, their eyes glaze over and we lose them to some Chinese company that sells a crap speed control, but doesn't tell the customer that they have to research/test/whatever their batteries before they use them.

So we give a nice general guideline, in a slightly humorous pamphlet. If the customer has a problem because he insists on using junk batteries purchased online from China, we give them a warranty replacement and a lecture on using good batteries and reasonable pinions, and warn them that the next failure caused by bad batteries will not be warranty.

Meanwhile, we continue to improve the controller as we see different failure modes, and make it more and more bulletproof. Nobody even knows that we are now shipping Version 4 of the MMM -- with a few minor changes to make them more reliable. Version 5 should be shipping the end of the year, with even more changes to improve reliability. Version 6 is in layout now, and will bring some more features, and more idiotproofness (that should be a word in the dictionary!) to the MMM.

So, our policy has been to be more "hands-off" about batteries - - support the customer, tell them to use good quality, name-brand batteries, but we won't call out brands specifically. And continue to make the controllers more able to deal with low quality batteries. In the long run, the market will drive the high quality batteries for performance reasons. Eventually even the cheapest batteries will have to perform adequately to compete on the open market.

What would really help is if people would stop encouraging the cheap junk entering the hobby market from direct-from-china internet based stores. They have no accountability, and can supply low quality goods with no chance of liability for the damage their junk causes.

Just my $.02

Patrick

Well I see it a little different I guess. I see it as the manufacturer you have to make your device idiot proof. I know what you are going to say "The world will always make a better idiot", but with that in mind. Castle should have known there are several brands out there that are not up to the task and explained how the system worked in brake mode and that if the batteries of poor quality then it could damage the ESC. There is no mention of that in the docs I have.

To me there should be a clipper circuit or something else to handle the spike created during this time, and have it built into the system, sure it adds weight and size, but do you want your system to have a bad rap? It matters not if this is a hobby, the manufacturer needs to make an effort to educate the masses buying their product. And they do but on this board not their website or documentation

Besides I have been researching the larger ESC's for some time now, since before the MMM came out. I called Castle and asked a bunch of questions but was never given a direct answer for current handling until recently by Patrick himself on this board.

You shouldn't have to search for a forum to find the answers you are looking for you should be able to get it straight from the manufacturer. The book is (was, haven't downloaded a new manual) seriously lacking on the technical side, and for something this technical it needs more meat, period. Having everything written down a little much? Well ok some things you have to save for yourself, but if batteries were this big of an issue it should have been in bold print on the front page of the pamphlet.

As far as having some intelligence, just look at my sig that I got from a milling machine we bought (condensed for space constraints). It’s all relative, if I would have just bought a MMM I would have set down and read the instructions (just like I did with my MM) and been off. Who is going to know about back EMF except someone who has an electronic background? This isn’t something that is commonsense. It is a flaw IMO.

Case in point, as I am sure you have read at least once we manufacture a small conveyor (among other things). It uses a stepper motor with integrated encoder and amplifier (read ESC), it also has digital and serial I/O. Basically we send it a position command (infinite in our case), Speed and Acceleration. Over the years we have had a few come back with the board damaged. About a year ago the manufacturer made a board revision that put a fuse in line with incoming power. On the output of the fuse is a Zener diode so if the voltage rises above a certain point it conducts and blows the fuse (there is also a TVS in there as well). Well I got in 4 units that had the fuse blown and the Zener shorted. On 3 of them I was able to replace the SMT fuse and everything was OK. The fourth though had a FET shorted as well. After speaking with their tech support I was told that a brand new motor only 17 days old (including shipping from Canada 2 Houston then to Ohio) would not be covered since the Zener was bad as well. I asked him why and what would cause this, he told me it happens during Regen. Basically the conveyor has solid SST rollers weighing about 12 pounds. We have a maximum Accel/Decel rate of 25 rps/s, which is quite slow. But if the conveyor gets jammed and then let go, it will speed up over our maximum speed and try to “catch up” with the position it’s supposed to be in. So basically it runs real fast then wham almost comes to a stop as it gets to position. As you can already tell the amount of force required to stop 12 pounds of weight almost instantly creates a large overvoltage and can take out the FET’s before the fuse can even react (besides fuses are S L O W, even fast acting ones). I asked what the fix was (besides their new motor we are working on the algorithm for), and was told I should need a “slave board” that has this protection built in. We never needed it in the past, since we run at a constant rate it hasn’t been an issue and we have used this motor for nearly 6 years. And you know what it’s in their book. The motor that we use is more suited for pick and place than the application we have it in now (we need something a little dumber).

Jeff

Patrick,

I understand your point about not naming names, but it wasn't until recently that the little piece of paper came out about C ratings. Also what's the deal with NiMh batteries wouldn't those have the highest resistance out there and cause damage to the controller? I haven't seen anyone mention that.

And how does one determine if their batteries are of good quality? My eyes don't glaze over so easily. If you are refering to a test to perform, I would be interested in that for sure, but if it's the C rating paper then well I already read it.


Regards,

Jeff

I would love to know how to determine if my batteries are good quality. Please share this information. Even if I buy proven batteries, they will eventually degrade. The same monitoring and evaluation needs to be for these as well. Please describe a test method for approving batteries for use with the MMM. Even if it requires an investment in an Eagle Tree or similar, many of use would be willing to invest the time and money.

Patrick, I recently picked up a Turnigy pack (4s 5Ah 30C) to see what all the hubub is about. I made sure it was balanced and all set, then ran it in my 8th scale buggy geared for around 35-40mph. I was quite surprised to see the results were better than I had hoped for. It literally puts certain other lipo manufacturers/resellers to shame. No, they aren't the "best" out there, but still VERY good, especially for the price. And, how does your tech staff know the ESC was run on inferior batteries vs simply good batteries pushed too hard? I would think the result would be the same.

I agree with you though; you can't name names in this sue-happy world we live in, even if it is true. Also, it is true you cannot cover every possible setup issue in the manual; doing so would make it so large that no one would ever read it (except maybe in the bathroom :smile:). Personally, on the next generation of ESCs that contain data logging (and therefore hall effect sensors), the firmware should be set up to continuously monitor current flow and voltage sag. If the voltage sags below a certain % of the nominal value, the ESC would automatically dial in punch control to lessen the bursts. Likewise, it can also monitor reverse current (provided a bi-directional HE sensor is used) and voltage on braking, and if the voltage and/or reverse current is too high, have the ESC automatically dial down brake force. Yeah, would make driving a little more unpredictable, but I would rather err on the side of caution. I suppose you could make this feature defeatable, but provide a disclaimer that any warranty claims are denied if disabled (and could look at the ESC log files to verify on return). Would give people the choice, but discourage random setting changes just because Joe Sixpack wants to do double backflips with inferior batteries, or is using good batteries, but is geared unreasonable.

Like Jeff and ticklechicken have asked: how does one determine their batteries are good or not using a logger? I personally look at voltage drop under load, and temps after a run as a guide. Loggers don't have sampling rates fast enough to catch ripple current, but I would imagine if v drop @ high currents is low, ripple currents will be low as well.

A little off-topic here, but I think the "ESC" should be programmed not to stop on a dime from the "catch up" time, but rather slow down over time. Same idea for the acceration part too IMO. In process controls, that is known as integrating. Regen voltage/current is a function of the amount of magnetic flux "stored" in the motor, the weight of the payload being forced to stop, and the stopping time. Since the first two aren't easily changed, that leaves the time factor.

As far as the NiMH issue; it's true they have higher resistance, but remember they simply cannot provide the current levels that any decent lipo can. I'm sure there are ripple currents with NiMH too, but since overall current is lower, so is the ripple. Of course, since NiMHs have a higher resistance, they heat up a lot more, which brings other issues, but that's not the point here. IIRC, a good NiMH can output 100A, but the voltage drops substantially. So, on takeoff, current peaks and voltage sags a lot. As the vehicle nears the set speed, current dwindles and voltage climbs back up. The effect is a more gentle acceleration. Kind of like a forced punch control when you think about it.

Back to the High vs Low gearing, are we on the right track? Obviously the batteries are the real issue, but could what I already theorized (higher gearing equates to more regen voltage) be partly the reason?

Jeff

It is a little off topic, but it illustrates the point that the manufacturer knows about this and has a fix. Also only the RT3 (currently ver 2.13) is capable of such commands, which are stored in a databank and are run when preset conditions are met. it's kinda like ladder logic and at present we have been Beta testing it when time permits. The motor is more suited for pick and place not a conveyor, Although the manufacturer said that a conveyor would be way more easy than constant starting and stopping. but it's the only thing that we can send commands serially. I was hoping to work with Castle on a new setup, but.....

When I first got my MM/7700 combo I used Duratrax 4200's and they did pretty well for a while. I bought the eagle tree and I saw peaks of over 125amps and the pack voltage would drop to about 5.5V, so I bet a Good set of NimH would put out a little better. It also makes me think that since the MM was intended for high Kv motors this kind of problem hasn't come up as it has with the MMM on 6S, with a low Kv motor and a ton of weight.

Jeff

The Chinese packs are getting better -- but consistency is still an issue. I spoke with a US battery maker a little while ago, and they told me that they reject about 15% of the cells they receive from their Chinese manufacturer, due to poor internal resistance. I'm sure that some of the Chinese pack manufacturers don't test to the same levels as other assemblers...

And yes, we can tell if the issue is current stress (pushed too hard) or voltage stress (bad battery for setup.)

Yes, on the Phoenix-ICE series we monitor voltage ripple both during braking and power -- and the controller automatically backs down if it sees voltage ripple go outside of a reasonable range. We are bringing this technology to the Mamba series in the future.

Agreed -- the best way to tell if a battery is good quality (barring using a Phoenix-ICE logger (which logs voltage ripple)) is to measure voltage drop at the battery terminals under a controlled load.


NiMh have the same issues as Lipos -- but as you point out, they also aren't as capable, so people are forced to use them in "softer" setups than Lipos.

As always, thanks for the answers Patrick!

Holy crap, V6 of the MMM already? I really need to stop being such a poster boy for buying the latest tech and instead wait for it to mature a bit more. Owell....


That being said, whats your official word on this gearing confusion?

so my repair that i got back last week is a v4?

Way I see it, the castle website recommends A123 Tanic packs.

http://www.castlecreations.com/produ...a_monster.html

So thats what I run, A123 packs, only diff is I changed the wires to 12 guage from 14

But I am still yet to see a Savage Flux on 6s fail on the 25t pinion, yet lots seem to on the 20t. That's the initial issue here isn't it?

If anyone has a link of a Savage Flux on 6s failing with the 25t pinion, please post it, otherwise all this talk about keeping the gearing low etc etc is kind of senseless, and the proof seems to point the other way.

Thank you for this information. For the MMM, do you have a minimum voltage drop which is acceptable, like 3.4 volts/cell? Or maybe it's a measurement relative to the packs voltage at that point in the run. For example, require that full throttle only produces a voltage drop of 0.5 volts/cell.

I'm very interested in finding packs that won't harm my MMM, and I want to be able to monitor the batteries through their life to verify they're still meeting the minimum requirements. Even the best cells will eventually start to have more and more voltage drop. How do I know when to throw them away to protect my MMM? I'm sorry to put you on the spot, but I would really like an actual number. I understand it's not a guarantee against anything going wrong, but I would value your opinion on this.

Patrick, How about a comic strip in the manual with Butthead telling Beavis not to be a dumbass with his rc truck and MMM? Or even a short cartoon of it on the website?

Or better yet in version 6 just a a sound chip and speaker that has Butthead saying "you dumbass" whenever some one does something stupid?

Not a good idea; it would be stuck in an infinite loop...

If anyone is willing to get on the brands of different battery packs, feel free to do so and just a heads up, Steve Neu might just change this C rating war. Please see the following: http://www.rcgroups.com/forums/showthread.php?t=1104509. I posted a couple of things in there and even included in my last post a few places that do test batteries specially lithium based ones. Those are some of the places I plan to use to test the cells I'm trying to get my hands on, but the military is a little bigger then I am :lol:. I know many places that do manufacture high quality cells, but they too can get caught in the C rating war and that's one of the reasons I push for a HV set up to keep my AMPs down on a safer side.

Dunno how the hell this went from a gearing question to Lipo C ratings, but whatever. :neutral:

it always does

And yet I am still waiting for someone to show me a Savage Flux on 6s with a 25t pinion smoking.

give it a raz yourself:yipi:
my recomendations, make sure you have top notch batts and watch your temps like a hawk and see what happens:wink:

Since people have mentioned it, I thought I would post something very important for this industry. If you don't think a standard for our lithium battery is needed, please buy MA packs and support them on their quest.

It's always been about the gearing, but braking is a part of the gearing, which could be part of the problem.

JEff

Well, good info nonetheless. It will be my last thread here. I've stirred up a hornets nest of hate against me and its best if I just leave here permanently for everyone sake.

Take care and happy RC driving all.

I don't quite get that but okay........I guess.........:neutral::oops:

DW he's sulking on all forums......

What? I don't get it, the only thing you did was get a good amount of info out, but didn't get your question answered, sorry we have asked again, but there may be politics involved in the answer. Who knows?

Nobody hates you or showed ill will to you. Granted the thread got somewhat off topic, but as I have read that's the way things go around here. One question gets asked and another pops up it's more like a transformation than a hornets nest. IDK maybe I sound like an ass sometimes, but that's just the way I am. Not trying to come off the way I do but I am usually posting from work and I still need to get other things done so I am a little curt at times. Sorry.

Jeff