My Sherman Trials, Tribulations, and Triumphs

[Alj]

17 minutes ago, Seba said:

Well, Veteran is using the same approach as Gotway - there is no dedicated temperature sensor. Instead, they just read temperature of MPU6050 IMU chip (the "gyro chip") that is located just below Bluetooth module (see picture below).

That is totally usual thing. Cost savings is more important that cost of human life. Different culture. If you want this to be done correctly you have to go to China and sit next to the engineer and point at those things. That's how it is done usually by western companies which manufacture things in Shenzhen.

[Esbu]

7 minutes ago, Alj said:

I'm not comfortable with "heavy use" therm here.

I used this term because when I think about it, protection against normal use is nonsense. If it destroys itself with normal use, it's shit.

I am sorry, but my English is bad and I often use translator. I hope you will forgive me and we will still understand each other.

[Alj]

5 minutes ago, Esbu said:

I used this term because when I think about it, protection against normal use is nonsense. If it destroys itself with normal use, it's shit.

I am sorry, but my English is bad and I often use translator. I hope you will forgive me and we will still understand each other.

Nope! I will never forgive you!!!!    j/k

[Esbu]

1 minute ago, Marty Backe said:

Rest assured, nobody associated with Veteran is reading anything said here. And historically they are very insular and have no interest in being told how to improve their design. 

Don't hold your breath 

This is a sad read, but their mentality is different and I can probably understand it. The first is money, the second is money, the third is money .....and only somewhere in the back it turns out that someone can use it, so it's for people.

[null]

Maybe we could throw in a third fan over the logic board, the enclosure seems roomy.

[Seba]

1 minute ago, null said:

Maybe we could throw in a third fan over the logic board, the enclosure seems roomy.

Personally I don't think that insufficient thermal management is a key problem here. From my perspective the main problem is with PCB layout that is not capable of handling high currents. Marty's board didn't failed because of MOSFET overheating, it was destroyed due to some short-circuit that caused severe arcing, leading to another, cascading short-circuits and finally catastrophic failure of entire board.

What caused initial short-circuit? We can only speculate. Maybe excessive current flowing over soldered wire-to-PCB joint caused solder to melt. Melted solder could move under wheel vibration and create a short-circuit. There can be many weak points that will enormously heat up under high current condition.

[erk1024]

When @Marty Backe was getting close to having the wheel fail, the motor was making a strange noise. What is that? Electric motors use the Hall sensor to know when to switch to the next set of magnets right? (Let me reiterate, I know nothing about electric motors) Does that noise mean that this cycle is breaking down? Would the motor making that noise cause things to overheat faster?

 

Edited July 24, 2020 by erk1024

[Esbu]

I talked to a friend who also rides on the EUC, and I asked him if he thought it was possible, for example, to build a testing laboratory for unicycles with community funding. The durability and capabilities of the new unicycle would be tested there. Then the unicycle would be certified, for example, by ELA - Euc Laboratory Aprroved. And we would know that paying attention to an unknown unicycle without an ELA certificate would not make sense. However, he told me that none of the Chinese manufacturers deal with this and they don't care. This is similar to what Marty said about my cooling treatment offer.

[Paradox]

1 hour ago, mrelwood said:

To me that sounds just like “look what you made me do!” as means to redirect the blame. No, if the user can dematerialize a vehicle equipped with an off-road tire by calmly riding off-road, it’s a badly designed product. The “design limits” have not been said excluding Marty’s overheat hill, quite the opposite, Marty was asked to stress the wheel. It’s absurd to expect that the rider would have to know the temperatures inside the wheel at all times when even the manufacturer is not capable of monitoring them closely enough. And it is well known that almost every other current wheel can manage the overhead hill just fine, either by riding all the way or forcing the rider off due to overheating. It’s not at all an unrealistic expectation from a current top-of-the-line EUC.

It’s crucial that the wheel is capable of monitoring itself and at least warn the rider when the wheel is being used outside its design limits.

It isn’t for many other wheels, why is it for the Sherman? Because of bad design.

So you agree, the Sherman didn’t behave as it was expected?

I do agree it did not perform as expected.  The wheel should have tilted back if there was time or cut off it was happening to fast as in the asian overheat hill test.    It should not self destruct in any situation.  Saftey mechanisms need better implementation or a redesign of the cooling process.

[Esbu]

3 hours ago, Alj said:

Pipes solve a problem where you have heat source in one place and heat sink in completely different place (due to form factor limitation) which is completely not an issue here.

Here we have heat source directly attached to the heat sink (via poor silicone insulation coupling) and any additional layers such as heat pipes will make things only worse.

I think any piece of copper is better than aluminum. When heatpipes are installed in the current heatsink, it will help. They do not necessarily transfer heat to a greater distance from the heat source.

[Alj]

28 minutes ago, Esbu said:

I think any piece of copper is better than aluminum. When heatpipes are installed in the current heatsink, it will help. They do not necessarily transfer heat to a greater distance from the heat source.

Copper is heavy. Aluminum is good enough here.

[Esbu]

1 hour ago, Alj said:

Copper is heavy. Aluminum is good enough here.

It is heavier than aluminum, but has better thermal conductivity.

[Michael Tucker]

Can't use heatpipes because of vibration, curbs/stairs and crashes.

[AtlasP]

5 hours ago, Esbu said:

If anyone from Veteran reads this, contact me, I will help you design a much more efficient cooling. I have experience with cooling overclocked processors with air coolers with minimal modifications. My Intel Core i5 Sandy bridge can run at 5.3GHz and handle all benchmark stress tests.

The old 2500K, I remember holding onto one of those for far too long because the o/c was just too good. :-) Although to be fair, overclocking one of the best/easiest-overclocking consumer desktop processors in history isn't exactly the best proof of one's cooling prowess--my mom could probably overclock one of those by just pointing a cheap Wal-mart articulating fan at it. ;-)

Edited July 25, 2020 by AtlasP

[Shield]

I understand that the board issues are more than just heat but would the use of mosfet heatsinks like these be of any benefit?

 

[bryon01]

6 hours ago, erk1024 said:

When @Marty Backe was getting close to having the wheel fail, the motor was making a strange noise. What is that? Electric motors use the Hall sensor to know when to switch to the next set of magnets right? (Let me reiterate, I know nothing about electric motors) Does that noise mean that this cycle is breaking down? Would the motor making that noise cause things to overheat faster?

 

Strong currents through the wires create strong magnetic fields.  Those fields push/pull on the other windings and iron.  The frequency of that push/pull is the groan you hear.  It's not bad by itself, but it indicates you are flowing enough current to melt a Veteran v1.0 control board.  So if your motor is groaning like that, you are likely pulling major amps, and that can be bad.

[bryon01]

1 hour ago, Shield said:

I understand that the board issues are more than just heat but would the use of mosfet heatsinks like these be of any benefit?

 

These wouldn't help, the aluminum extrusion the mosfets are on are better than this.  The mosfets didn't fail, the current through the board traces did.  Probably melted the solder and shorted the battery leads.

[mrelwood]

9 hours ago, erk1024 said:

When @Marty Backe was getting close to having the wheel fail, the motor was making a strange noise. What is that?

When Marty started the overhead hill, the wheel was already grinding more than before, so something had already started to fail. When I toasted my MSX, the wheel sounded like it was grinding pebbles, and before I had time to realize what’s going on and react, in just two seconds the board and the motor failed.

I think the grinding comes either from a component on the board starting to fail, or the motor wires melting and getting very close to each other. Either way, it’s a certain tell that something has damaged and the wheel will very soon fail.

I’m of course not talking about the regular motor coil cogging that every wheel makes (GW being the loudest) when stressed at slow speeds. But the one that has a varying pitch like a combustion engine, and can also be heard at higher speeds and lower burdens. 

9 hours ago, Esbu said:

If anyone from Veteran reads this, contact me, I will help you design a much more efficient cooling.

Several people have also offered their help in translating the manuals and apps for free, and still none of them has taken up on the offer. Surely helping in the actual design is yet much taller order, no matter how much sense the both offers would make in our minds.

Edited July 25, 2020 by mrelwood

[Esbu]

5 hours ago, AtlasP said:

The old 2500K, I remember holding onto one of those for far too long because the o/c was just too good. :-) Although to be fair, overclocking one of the best/easiest-overclocking consumer desktop processors in history isn't exactly the best proof of one's cooling prowess--my mom could probably overclock one of those by just pointing a cheap Wal-mart articulating fan at it. ;-)

Yes, it is one of the best overclockable CPUs ever. However, when a processor with a base frequency of 3.3GHz is overclocked to 5.3Ghz, so that such a clock frequency can be achieved at all, such a processor is usually cooled by liquid nitrogen.

[Chriull]

20 hours ago, meepmeepmayer said:

In that second Sherman kill video, it fries after like 10 seconds on a very steep test hill. What temperature sensor is going to engage before it's too late there?

Some mounted on heatsinks directly aside the mosfets. But this still could ge to slow.

Afaik there exist mosfet driver circuits that deduct the mosfets junction temperature by measured ng their specific currents/voltages.

Another "easy" way would be to sum up the power dissipation of the mosfets and estimate their temperature by this.

16 hours ago, Marty Backe said:

Great info. Thanks. So to be semi-effective they would probably have to add a bias to whatever temperature they read from the IMU. Hopefully they are doing something along those lines.

It won't be as simple as a fixed bias - there is a very fast heatup inside the mosfets, quite "instant" with the square of flowing current. This heat gets slower transferred to the heatsink and from there over time to the ambient temperature which is measured on the board.

While this happens the fans blow some of the hot air out of the chamber...

With some trial, error and testing some nice heuristics should be found to handle this problem. And/or supported by knowledge and experience...

And in the same way other weak spots. Burdens on the pcb tracks, etc...

16 hours ago, erk1024 said:

When @Marty Backe was getting close to having the wheel fail, the motor was making a strange noise. What is that? Electric motors use the Hall sensor to know when to switch to the next set of magnets right? (Let me reiterate, I know nothing about electric motors) Does that noise mean that this cycle is breaking down? Would the motor making that noise cause things to overheat faster?

 

9 hours ago, bryon01 said:

Strong currents through the wires create strong magnetic fields.  Those fields push/pull on the other windings and iron.  The frequency of that push/pull is the groan you hear.  It's not bad by itself, but it indicates you are flowing enough current to melt a Veteran v1.0 control board.  So if your motor is groaning like that, you are likely pulling major amps, and that can be bad.

This could be one effect, from my readings(1) so far i'd tend to account most of this "strange" sound to trorque ripples/cogging torque.

At low speeds the rim with the permanent magnets is pushed a position to the next. Only at higher speeds this is "smoothed" by inertia.

The higher the burden (current) the "harder" this steps.

With some bearing/axle play some resonances with the board gyro can amplify this behaviour. Also a small crack in the shell can amplify this behaviour (happened with an ks18xl - started such sounds at stronger braking maneuvers by this)

As another point firmware current limiting could create/amplify this, as the current is "prematurly" cut during a pwm cycle - thus increasing the torque ripple..

16 hours ago, Seba said:

Personally I don't think that insufficient thermal management is a key problem here. From my perspective the main problem is with PCB layout that is not capable of handling high currents. Marty's board didn't failed because of MOSFET overheating, it was destroyed due to some short-circuit that caused severe arcing, leading to another, cascading short-circuits and finally catastrophic failure of entire board.

What caused initial short-circuit? We can only speculate. Maybe excessive current flowing over soldered wire-to-PCB joint caused solder to melt. Melted solder could move under wheel vibration and create a short-circuit. There can be many weak points that will enormously heat up under high current condition.

Would be my guess too looking at the pictures! Not to forget a desoldered battery cable can freely move in this area and the capacitor has non insulated legs there, which are on full battery voltage level!

Maybe we'll see as an next iteration solid copper/aluminium bars as supply chains with the components welded/crimped/screwed to them. As a first step the battery wires should be mounted like the motor wires and not soldered directly on the pcb anymore.

The board layout seems to be made somewhat like this already - two nicely thick traces for supply voltage alongside the pcb.

(1) just googled again for "accoustic noise by torque ripple" which leads to many papers like

 https://www.google.com/url?sa=t&source=web&rct=j&url=https://jpels.org/digital-library/manuscript/file/17200/12_JPE-16-12-083.pdf&ved=2ahUKEwj0nviStOjqAhVLa8AKHbwtDsgQFjADegQIAhAB&usg=AOvVaw2ybXNZHA-I2OpJaO4-Fb6n&cshid=1595680959459 

or

 https://www.google.com/url?sa=t&source=web&rct=j&url=https://e2e.ti.com/blogs_/b/industrial_strength/archive/2016/02/25/acoustic-noise-in-home-appliances-due-to-torque-ripple-in-motor-drives-part-2&ved=2ahUKEwj0nviStOjqAhVLa8AKHbwtDsgQFjAEegQIBhAC&usg=AOvVaw1328tdC2bqLLJu38O3-ORT&cshid=1595680959459

[erk1024]

2 hours ago, Chriull said:

just googled again for "accoustic noise by torque ripple" which leads to many papers like

Super interesting! Thanks for the links!  

[bryon01]

4 hours ago, Chriull said:

This could be one effect, from my readings(1) so far i'd tend to account most of this "strange" sound to trorque ripples/cogging torque.

At low speeds the rim with the permanent magnets is pushed a position to the next. Only at higher speeds this is "smoothed" by inertia.

The higher the burden (current) the "harder" this steps.

With some bearing/axle play some resonances with the board gyro can amplify this behaviour. Also a small crack in the shell can amplify this behaviour (happened with an ks18xl - started such sounds at stronger braking maneuvers by this)

As another point firmware current limiting could create/amplify this, as the current is "prematurly" cut during a pwm cycle - thus increasing the torque ripple..

I don't agree with your position.

Any dynamic force, aka changing force, in a motor will excite all aspects of the motor, the plastic housing, the windings, the magnets, etc.  You can assume that the further from the excitation, there was increased dampening based on the materials and physical shape of the structure.  All mechanical systems have resonance points, where something exciting them at that frequency will cause large amplitudes.  That mechanical excitation can produce audible sound if it is in the range of human hearing  in both magnitude and frequency.  The motor is not smoothed out by inertia at a certain speed, it is just that the frequency has moved away from resonance with the mechanical structure of the motor.  The motor has the same inertia at any speed, up until the point parts start flying off of it.

In our BLDC motors used for EUCs, the cogging torque has actually been minimized.  You can test this yourself by spinning the wheel with the EUC off.  Do you feel it cogging?  Maybe a little, but likely not a lot.  Some cogging torque does exist, but noise from cogging torque is minimal in a motor designed to not have a lot of cogging torque.  By the fact that the Veteran does NOT sound like a chainsaw anytime it is moving, under light load, it is OBVIOUS that this is not cogging torque.  It is in fact, the phase current excitations with the permanent magnets in the rotor.  Once you flow current through the phase wires you are creating an electromagnet around the iron core the copper is wrapped around.  The strength of that electromagnet is proportional to the current flowing.  The windings themselves also push/pull against each other.  The housing is being vibrated by all the forces, etc.  Whatever the exact source, the cause is plain. The phase current in the motor is at a frequency that it is exciting some mechanical structure of the EUC.  It likely only happens at very high current (so therefore high forces) and at a certain speed.  At that speed, some combo of the PWM switching of the phase current, and the longer period of the phase current frequency itself, or a beat of those frequencies (f1-f2 or f1+f2), is exciting the structure.  Any change in the phase current is directly correlated with force excitations in the motor, and the higher the current, the stronger it is being excited.

Torque ripple is a change in current, and as I said above changes in current equals changes in forces which can equal noise from mechanical excitation of the structure.  That said, torque ripple is a tiny change in current compared to the FETs literally chopping 100A of current off and on repeatedly.  Hence, as I said before, the noise is due to the extreme current in the phase wires. It is implied that it is actually the high changing current creating changing force that is actually creating the noise.  The current is not continuous.  If you monitored the current of a Gotway motor on an oscilloscope, also famous for making grinding noise from a stop, you'd see the current was extremely high in those slow speed cases too, as any EUC is essentially giving max current when you first stand on it if you were the least bit off balance or if you are doing forward/back reverses.  If you don't want that noise you need a tighter stiffer motor, that moves the resonance to a range that is not excited by the stator currents in a range that is audible.

[wwwooooqq]

The heat generation is related to the current. The heating of the wire and the melting of the rubber prove that its wire cannot meet too much current. I think the design of its heat dissipation system is unreasonable, causing local high temperature, and the enclosed environment is like an insulation system instead of a heat dissipation system, excellent design doent need to use a fan to dissipate heat, and a bad design cant dissipate heat with a big fan. can see that its mos are not evenly distributed on the radiator, but concentrated in one corner, which part of close to the fan is gets good heat dissipation, and the other side is not only without the aid of a fan and not enough for the thermal capacity buffer, I started to worry about its in summer

[Chriull]

On 7/25/2020 at 8:05 PM, bryon01 said:

Do you feel it cogging?  Maybe a little, but likely not a lot.  Some cogging torque does exist, but noise from cogging torque is minimal in a motor designed to not have a lot of cogging torque.

Yes - that was one translation i used googling and dictionaries which meant something different than i meant. Your explanation of cogging torque is nicely explaining it's meaning and showing it's irrelevance here. As it is also described as "no current torque" in the second link of my post - i wanted to remove it than from my post but forgot this before submitting it...

On 7/25/2020 at 8:05 PM, bryon01 said:

Torque ripple is a change in current, and as I said above changes in current equals changes in forces which can equal noise from mechanical excitation of the structure.  That said, torque ripple is a tiny change in current compared to the FETs literally chopping 100A of current off and on repeatedly.  Hence, as I said before, the noise is due to the extreme current in the phase wires. It is implied that it is actually the high changing current creating changing force that is actually creating the noise.  The current is not continuous.  If you monitored the current of a Gotway motor on an oscilloscope, also famous for making grinding noise from a stop, you'd see the current was extremely high in those slow speed cases too, as any EUC is essentially giving max current when you first stand on it if you were the least bit off balance or if you are doing forward/back reverses.  If you don't want that noise you need a tighter stiffer motor, that moves the resonance to a range that is not excited by the stator currents in a range that is audible.

As described (or at least how i understood it) in the first paper i linked, the main portion of "torque ripple" comes from the current changes by the different commutation phases. By the difference in the commutation pattern and the back emv of the motor (winding characteristics). Of course this "maladaption" is proportional to the value of the phase current.

Just "measured" the main harmonics of @Marty Backe's last bit of hill climbing - seems to be at ~150Hz. Taking the formula (6) from the paper 

"f i th = i*k*p*n/ 60 (6) where th i f is the th i order harmonics of the motor commutation frequency, i is the number of the harmonics order, k is the number of steps of commutation in one electrical cycle, p is the number of stator pair of poles, and n is the rotational speed (r/min). In the CV-mode and VV-mode k = 6. Thus, the fundamental commutation frequency 1 th f is 0.1pn ."

gives for the veteran (54 coils -> 27 pole pairs, 20 inch tire ~ 1.6 m circumference) for 150 Hz as the first harmonic 55 rpm ~ 1,5 m/s ~ 0,4 km/h.

Which seem to fit quite well with the video.

The "150 Hz" are, for me surprisingly high - i would have estimated the frequency much lower. As the "stuttering noises" while hard acceleration and braking. Some years ago this stuttering noise while acceleration was explained from a gotway representative to arise from their ?120 A? firmware current limiting. Will have to measure such stuttering braking noise once too if this corresponds to the "main torque ripple" frequency - current limiting occurs "within the commutation pattern" and hence increase the maladoption or sets in independently...

Edit: .... And this numbers could be just about fitting but are maybe just some "initial starter". Just looked at the video linked in https://forum.electricunicycle.org/topic/18545-tesla-motor-noise-and-battery-charge-questions/ . Here by a loose motherboard caused oscillation of about 120 Hz. And @Marty Backe reported some strange vibrations of this wheel before. Something a bit loose caused vibrations (oscillations) via the gyro sensor... Beeing stimilated/induced by torque ripple?

 

 

Edited July 27, 2020 by Chriull

[Marty Backe]

4 hours ago, Chriull said:

Yes - that was one translation i used googling and dictionaries which meant something different than i meant. Your explanation of cogging torque is nicely explaining it's meaning and showing it's irrelevance here. As it is also described as "no current torque" in the second link of my post - i wanted to remove it than from my post but forgot this before submitting it...

As described (or at least how i understood it) in the first paper i linked, the main portion of "torque ripple" comes from the current changes by the different commutation phases. By the difference in the commutation pattern and the back emv of the motor (winding characteristics). Of course this "maladaption" is proportional to the value of the phase current.

Just "measured" the main harmonics of @Marty Backe's last bit of hill climbing - seems to be at ~150Hz. Taking the formula (6) from the paper 

"f i th = i*k*p*n/ 60 (6) where th i f is the th i order harmonics of the motor commutation frequency, i is the number of the harmonics order, k is the number of steps of commutation in one electrical cycle, p is the number of stator pair of poles, and n is the rotational speed (r/min). In the CV-mode and VV-mode k = 6. Thus, the fundamental commutation frequency 1 th f is 0.1pn ."

gives for the veteran (54 coils -> 27 pole pairs, 20 inch tire ~ 1.6 m circumference) for 150 Hz as the first harmonic 55 rpm ~ 1,5 m/s ~ 0,4 km/h.

Which seem to fit quite well with the video.

The "150 Hz" are, for me surprisingly high - i would have estimated the frequency much lower. As the "stuttering noises" while hard acceleration and braking. Some years ago this stuttering noise while acceleration was explained from a gotway representative to arise from their ?120 A? firmware current limiting. Will have to measure such stuttering braking noise once too if this corresponds to the "main torque ripple" frequency - current limiting occurs "within the commutation pattern" and hence increase the maladoption or sets in independently...

Edit: .... And this numbers could be just about fitting but are maybe just some "initial starter". Just looked at the video linked in https://forum.electricunicycle.org/topic/18545-tesla-motor-noise-and-battery-charge-questions/ . Here by a loose motherboard caused oscillation of about 120 Hz. And @Marty Backe reported some strange vibrations of this wheel before. Something a bit loose caused vibrations (oscillations) via the gyro sensor... Beeing stimilated/induced by torque ripple?

 

 

This is a very deep post