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Inmotion V12 HT board: "More durable MOS"


supercurio

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  • supercurio changed the title to Inmotion V12 HT board: "More durable MOS"
1 minute ago, ESB said:

Inmotion really messed up their reputation for safe and reliable wheels in my eyes

Maybe they can spin off the V12 under a new brand name... InMoBegode

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Posted (edited)
2 hours ago, The Brahan Seer said:

There is a lot of assumptions here. How do you know they didn't just upgrade the MOSFET's on the V12 HT because of the uprated motor? 

So the MOSFET's are more durable compared to the standard ones.  It doesn't mean they are deliberately hiding anything.

Inmotion would have far too much to lose to try and pull the wool over the eyes of its customers.

Yes fair comment.

I agree there's some reading between the lines, but it's based on analyzing the whole chain of events from the perspective of the manufacturer, the system of incentives in place as well as what came out candidly in their own statements.

The key IMO here is that okay V12 HT board can deliver more power, 23% in their own material. More power, bigger MOSFETs, makes sense.

However what doesn't make sense is given the specified power for each model, the new board should not have "More durable MOS". V12 should have durable MOS. V12 HT should have durable MOS. If V12 HT has "More durable MOS" it automatically implies that V12 MOS lack durability.

That's why I imagined this little story of the marketing team asking around what they could add to their brochure, because it's usually what happens when you announce a new product and create marketing materials for it (unless you completely make stuff up, which is also a possibility)

It's like you'd say that the Monster Pro has more durable MOS than the Kingsong 14D. Well that's a bit of an odd statement isn't it, unless you know about flaws affecting the 14D MOS.

Any non-defective MOSFET will be "durable" if used within its specifications + an extra margin on top (the industry standard). Inmotion missed both on the V12.

 

3 hours ago, Khazik said:

From my layman's understanding, performing the spin test has introduced "immediate permanent damage" since the MOSFET's aren't up to spec in the first place; if your wheel passed (like mine did the first few times), the 'sooner or later' fail date becomes more 'sooner' than later. 

 

100%. My wheel passed a few tests, but something just didn't feel right w/me. I had a nagging feeling I just had to do it one more time - failed. 

I feel the same:

Initially I thought maybe if I run the stress test before every ride, then I know that the MOSFETs are still good.

But wouldn't the stress test accelerate damage every time, therefore increasing the risk for that ride? Knowing that the hardware is already used beyond capacity and that several people who cutout and crash had a blast on the previous fast ride, and their wheel died on the next chill one.

It all seems like a bad idea, kind of entering Darwin Awards voluntarily knowing that the hardware design is faulty no matter what.

Edited by supercurio
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I'd bet a month's wages that the engineers warned about using those MOSFETs, but the bean counters overruled them. Inmotion screwed up here in a big way.  They always had a reputation for building , well made, reliable and durable wheels. That was their biggest asset, and they threw it away for some short term profit. A big disappointment.

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At least this issue has appeared relatively early in the production run, not just when the overloaded FETs fail prematurely from aging - two or three years from now and with thousands more wheels sold.

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Posted (edited)

@rolis happy it makes sense to you too.

Initially I found the argument of change in MOSFET production quality believable, like if fakes made their way into the supply chain and Inmotion was an unlucky causality.

It changed when the cutout list and furthermore, your test list highlighted that a number of 1st batch wheels failed just as well.

@RagingGrandpa agree it's speculation, but it sounds plausible.

Maybe they even thought it was wiser to use a known part that served them well in the past than a different one unproven to them, and it backfired.

 

Either way, with enough unlucky "testers" out here we know they didn't pick the right components, and it's time to move on to different ones instead of relying on golden samples of a 100V one.

Edited by supercurio
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1 hour ago, rolis said:

Change of MOSFET provider?

Unfortunately mosfets are not MacBooks, and while it sounds wild, things like the provider can make an actual difference. Even I know that much.

Electron tubes/valves are an overly extreme example, but I’ll say it anyway. Even the most modern manufacturing processes yield tubes that vary significantly in two crucial values. There are only a few tube factories in the world, but there are many tube brands.

What the brands do is they buy truckloads of tubes, let them run for a while, and measure each tube so they can be sold in pairs and sets of 4 that match well. The ones that don’t, are either sold to a brand that sells cheaper tubes, or simply relabeled and sold as a different brand.

 What some distributors do is they buy a large batch and re-measure them themselves, and if they do it well, they can even create a fame for selling good tubes. But even they sell the cheaper tubes from the same exact factory, same exact production line, same production batch.

I don’t know how large the variation is in power mosfets in general, but at least the small Fet J201 biases extremely differently from one unit to the next, within the same batch, all the way to not functioning properly if swapped to another in-spec unit. And even if they are properly biased or the biasing were automatic, two identical products can sound slightly different.

 That’s the world of modern electronics that I know of. Nothing to do with identically behaving MacBooks, which wouldn’t surprise me if the relatively high price were partially explained with simply tighter product tolerances, ie. more scrap units.

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2 hours ago, supercurio said:

Trust needs to be earned, it is not an absolute thing, it's much more fluid than that, and it is complex at the scale of an organisation like a whole company where each individual can make mistake.

I’m sure it is. I do wonder though that if they can simply decide to use a wrong component for not having to wait, how has the original trust for a safety oriented brand been able to form? That they could’ve done things like that many times before, but their “luck” simply ran out this time? All I have to go for is my reasoning, and it considers the scenario more improbable than probable.

2 hours ago, supercurio said:

Is your point: They built many reliable wheels, therefore all the wheels they build now and in the future are reliable as well?

Absolutely not! But considering that numerous forum members have painted blame on various EUC manufacturers many times before, and disregarding the ones related to GW, I think they have been mostly in the wrong. That doesn’t mean that they will always be wrong, but comparing the probabilities of a self acclaimed alarmist and an experienced and reputable company, it’s pretty obvious where one should place the bets.

2 hours ago, supercurio said:

Using a component within its specification allows it to be durable.

How durable?

2 hours ago, supercurio said:

you cannot compare with a linear scale of people being different height.

Durability may not be a linear scale, but it sure ain’t a vertical one either. At least in my language.

 

2 hours ago, supercurio said:

After reading everyone knowledgeable's posts in the related threads, you will find each describe the design as faulty.

When Tawpie answered my question about whether the mosfets see the full battery voltage, the answer was that they’d need to see the schematic in order to be sure.

 

2 hours ago, supercurio said:

A MOSFET with breakdown voltage of 100.0000V is within specification, despite it might make the V12 self-balancing algorithm fail on a bump

And if that were the case, you’d be right and the mosfet was a wrong choice for the intended use. But I’m definitely not able to assess all the relevant factors that are unavoidably at play here. To me the main questions are whether the steps Inmotion has taken so far are sufficient or not, and whether they have been truthful in their public comments. So far I don’t have a reason not to believe them.

 

2 hours ago, supercurio said:

If not, please point out which components are.

You already know my answer to that one. Besides not having anywhere near the required knowledge, I don’t plan to own a V12, so spending more time with the matter than I currently am is just not beneficial to me. I will hear how all this pans out before ordering myself a “V13” anyway.

 

2 hours ago, supercurio said:

the stress test make 25% of the MOSFETs fail

You probably mean 25% off the units? There are 12 of these driver mosfets in each V12. 25% failed wheels is much more than the last I checked, but it would still be only about 2% of the actual mosfets.

 

2 hours ago, supercurio said:

"Nominal values for components are relatively conservative"

Considering that even these Chinese PR people sometimes need a translator to understand or type in English, I do hope that the tone that irks you in that message is not fully intended.

 

2 hours ago, supercurio said:

My goal is to pressure them to provide replacement boards using components within their specification so they have a chance to operate reliably and keep our rider community safe.
And that board seems to be designed already for the V12 HT variant.

I’m glad that your intent is more structured than what the first post made me think of. And let me be clear, I’m not standing in your way. But I do have a tendency of replying to comments that I consider overshot.

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34 minutes ago, mrelwood said:

I’m sure it is. I do wonder though that if they can simply decide to use a wrong component for not having to wait, how has the original trust for a safety oriented brand been able to form? That they could’ve done things like that many times before, but their “luck” simply ran out this time? All I have to go for is my reasoning, and it considers the scenario more improbable than probable.

Maybe we will know later what happened and how.

There must be turmoil in the company with strong disagreements on how to handle things, and it will take weeks at the minimum to see movement.

34 minutes ago, mrelwood said:

You already know my answer to that one. Besides not having anywhere near the required knowledge, I don’t plan to own a V12, so spending more time with the matter than I currently am is just not beneficial to me. I will hear how all this pans out before ordering myself a “V13” anyway.

I understand. You see me more invested in the topic than most because I have a V12 incoming soon to replace my V10F I can't decide yet what is the best course of action.

If I bought it at current ongoing price I would have canceled a long time ago: it won't make it for the winter riding season which was its original purpose.
I bought with a pre-order discount so it's harder to cancel. But then if I do cancel, someone else less informed might get hurt. I don't want that on my conscience either hence the motivation to find a better solution.

34 minutes ago, mrelwood said:

You probably mean 25% off the units? There are 12 of these driver mosfets in each V12. 25% failed wheels is much more than the last I checked, but it would still be only about 2% of the actual mosfets.

Good catch! I mis-spoke here: 25% of wheel failure on the stress test is not 25% of MOSFET since there's 12 of them and each of them failing, multiplying the risk of wheel failure 12x.

34 minutes ago, mrelwood said:

Considering that even these Chinese PR people sometimes need a translator to understand or type in English, I do hope that the tone that irks you in that message is not fully intended.

I disagree on that one, it's far too generous to give them a pass on a clearly false statement citing potential loss in translation.
What else could they have meant with the formulation "Nominal values for components are relatively conservative" which could have been mistranslated, besides what it says.

IMO, either:

  • genuine belief that the components are suitable, despite 22% real-world wheel failure rate, which indicates some amount of denial or self-delusion
  • damage control PR attempt

In a way it doesn't matter since reality disprove the statement: if components has been indeed conservatively selected, they would not pop on 22% of wheel across all production batches.

34 minutes ago, mrelwood said:

I’m glad that your intent is more structured than what the first post made me think of. And let me be clear, I’m not standing in your way. But I do have a tendency of replying to comments that I consider overshot.

Thanks, it's good advice: I'll look into how to describe the intent better in posts itself instead of clarifying later.

It's great to have people willing to write replies with counter points in order to keep the discussion balanced instead of turning into an echo chamber.

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Which MOSFETs have the previous 100V wheels used? Does Gotway use ones listed for higher voltage? My experience in robotics tells me that the specification  usually accounts for normal intended usage with enough tolerance. Meaning you don’t usually need to use 150V parts for 100V wheel just because voltage might sometimes go over the spec. 
 

Also:

"never attribute to malice that which is adequately explained by stupidity."

I’m not a fan of jumping into conclusions and claiming purposeful intentions in bad faith for saving some money. The cost of losing the reputation is too much. They’d be very stupid to do so. That’s why I’ll assume first an honest mistake or actual supplier issue (happens a lot in China). But let’s see how it develops. Definitely good to discuss this. 

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24 minutes ago, RagingGrandpa said:

(we still don't know if the failure rate is due to variation alone; or if truly defective parts that don't meet the minimum spec made it into production)

We still don't know, but a trusted distributor told me 30% of his summer batch V10F failed also. And aren't they supposed to use the same Infineon IPP023N10N5?

It was not discussed anywhere but Inmotion has this information, although they left the distributor in the dark without answer.
This probably contributes to their conclusion that V12 failures are due to defective parts in the in the FET supply instead of a design issue.

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