Downhill + 240 LBS = Torn off ligaments and three fractures

[Chriull]

9 minutes ago, Hunka Hunka Burning Love said:

I wonder though whether there is a possibility that the fall in the OP's case could have been due to rider error and maybe not a fault of the wheel?  For a new rider who has his first wheel for 1.5 wheels to tackle the steep hills of San Fran that's pretty ballsy.  Add in some subconscious questions and borderline weight limits, could that possibly be a factor in the accident?

6 minutes ago, Cerbera said:

I have to admit I did wonder about rider error when I saw 1 and a half weeks... but 6mph is a perfectly reasonable speed to be going to down a hill like that, so even if the riding was terrible (and I'm not saying it was !) we are still left with the problem of why the wheel shut off.

Imho after 1 1/2 weeks the riding will not be as smooth as once the "body" learned to balance perfectly, so the wheel has to balance much more and by this has to dissipate more power... Could maybe have some influence?

 

9 minutes ago, Hunka Hunka Burning Love said:

 Could the tire have lost traction on a slippery spot maybe?

Also a very good point - some slippery spot (overseen wet leaves, etc) going down a decline could/should feel like the wheel starts freewheeling as after a BMS cut/off or as some controller overheat/etc protection kicks in...

[lizardmech]

Does it still work? BMS probably cut out if it still works. It might also be possible to over volt the board while going down hill, if battery resistance becomes too high it's possible induction could push the VBus beyond it's rated voltage, but it would have to be tested to see if it's possible. The EUCs all use synchronous rectification as far as I know, so the reverse diode isn't used much. Mosfet internal diodes have significant voltage drop, I imagine they would burn up almost instantly if used.

[The Fat Unicyclist]

8 hours ago, Cerbera said:

I have to admit I did wonder about rider error when I saw 1 and a half weeks... but 6mph is a perfectly reasonable speed to be going to down a hill like that, so even if the riding was terrible (and I'm not saying it was !) we are still left with the problem of why the wheel shut off.

As a rider who regularly rides downhill with 240lbs+ I can say 6mph is significantly fast! 

On steeper hills (and mine compares with some of those in SF), that much weight adds a lot to the effect of gravity - anything faster than 5~6mph and I question whether my wheel would have enough power to stop me. 

So a "fresher" rider may inadvertently push the wheel past the torque limit...

[ImpulseZeo9201]

Ok, to answer hunkas question: I did fall backwards, in part. 90% of my weight was on my heels. I distinctively remember the clunk, no debris, water etc. on the sidewalk though. My right foot hit the pavement and my other foot held on for about a second longer.

I like lizardmech 's explanations. My subconscious could have to do with it. I am sure however that it was an accident caused by my machine. I felt the magnets holding me steadily decelerating and then for a split second they cut out and I tumbled.

I have noticed the nurse in the hospital trying to lift it and I advised to turn it on, so he can wheel it. The wheel acted erratic, as a stutter. So he turned it back off. Ill test it when I get home.

 

[ImpulseZeo9201]

31 minutes ago, The Fat Unicyclist said:

As a rider who regularly rides downhill with 240lbs+ I can say 6mph is significantly fast! 

On steeper hills (and mine compares with some of those in SF), that much weight adds a lot to the effect of gravity - anything faster than 5~6mph and I question whether my wheel would have enough power to stop me. 

So a "fresher" rider may inadvertently push the wheel past the torque limit...

Yes I agree, I go a bit slower than I feel I probably could (to be safe). And again perhaps my degrees are a bit off and it was 13-15.

I went pretty much to the highest hills twice Filbert Street (31.5% (17.5°). during my ride and the accident happened at the last bit which was slightly less steep.

 

 

[The Fat Unicyclist]

Not a bad hill!

I must say I am tempted to try Baldwin Street here in New Zealand... But at the same time, the physics would make me rather nervous   

Perhaps I need to learn to ride backward and then go downward while facing up? 

[ImpulseZeo9201]

Haha yes that would be awesome

[Hunka Hunka Burning Love]

I wonder whether all the previous hill climbing may have heated up the MOSFETS and that last downhill while braking might have done them in with extra heat and current.  If the wheel is acting all stuttery, that might indicate a MOSFET failure.  Will you be having Tec-Toyz take a look at it to determine the reason for failure?  I've seen @Chriull post a couple of his 9botmetric graphs on his KingSong hitting 58A peak while coming to a stop on a downhill and about 48A just idling next to a lamp post on a downhill path?  Maybe he can clarify that and tell us what his weight is.  

I have a feeling what happens when too much force is exerted on the electric motor is that there is heat generated, high current, increase in MOSFET temperature and potential failure if the components cannot deal with it.  Call it a slow controller board death with heat and excessive current as the prime suspects.  When a wheel gets stuck under a park bench, I think a similar problem happens, but the high current that the wheel is drawing to try to move must burn the MOSFETs out quickly.  Maybe.    Don't mind me - I'm just pretending to theorize what I am talking about.

I wonder if doing some @EUC Extreme mods might be prudent for heavier riders as the extra weight and steep hills might be stressing the wheel over its limits.  You might need modify your wheel for heavy duty usage.  I'd also recommend maybe not doing too many up and down hills unless you give the controller board a chance to cool off in between or monitor the temperatures carefully.

It would be interesting to see various weights braking while going downhill to see what the temperature effects are.  There must be a limit as to how much weight these motors can handle.  240 pounds might be fine with a cool MOSFET heatsink whereas 500 pounds, 1000 pounds?  Something must pop, and it would be educational to find out the process by which it occurs.

I wonder whether intermitantly braking while going down steep hills is better?  I know with cars riding your brakes down a long hill really heats up the pads and calipers and isn't very good for them so they recommend moderate pressure to slow down, letting go, and then repeating as often as needed to keep the speed you want.  Perhaps cycling the braking action on an EUC for heavier riders or where lots of hill climbing and descending is needed might be something to consider?

[ImpulseZeo9201]

Yeah, like I said I will test the unit once I'm home. I never thought of heat as a factor. Is there a blackbox-ish thing inside the GW app for iOS or the Unit itself?

[Hunka Hunka Burning Love]

I think there's Wheelog that is able to read data from the wheel, but I don't think it records it.  It's more like live telemetry?

Also 9Bmetrics works, and it records the data into charts.

Here's an example of a recording that I made on my run:

 

[steve454]

3 minutes ago, Hunka Hunka Burning Love said:

 

I think there's Wheelog that is able to read data from the wheel, but I don't think it records it.  It's more like live telemetry?

 

I wonder if @EUC Extreme knows, he probably knows every kind of cutoff a Gotway can do?

[steve454]

On 11/16/2016 at 0:47 PM, ImpulseZeo9201 said:

Yeah, I still like the idea of going down a hill backwards best. If you fall at least its on your hands. Even though Id like to see someone pull that off.

That would be something that @Hirsute @Sidestreet Reny @Jonathan Tolhurst or @Toby Stevens could probably do.  That would be a good trick.  I'd like to see a video of that also

[Chriull]

9 hours ago, Hunka Hunka Burning Love said:

I've seen @Chriull post a couple of his 9botmetric graphs on his KingSong hitting 58A peak while coming to a stop on a downhill and about 48A just idling next to a lamp post on a downhill path?

These were just short peaks and should not be really relevant for heating up the mosfets... Just could give them the last "punch"....

Quote

 Maybe he can clarify that and tell us what his weight is.  

I have something around 90kg/200lbs.

Quote

I wonder if doing some @EUC Extreme mods might be prudent for heavier riders as the extra weight and steep hills might be stressing the wheel over its limits.  You might need modify your wheel for heavy duty usage.

His heatsink mod is for sure very recommendable - if one can do it! Also the axle mounting modification looks great...

Quote

 I'd also recommend maybe not doing too many up and down hills unless you give the controller board a chance to cool off in between or monitor the temperatures carefully.

It would be interesting to see various weights braking while going downhill to see what the temperature effects are.  There must be a limit as to how much weight these motors can handle.  240 pounds might be fine with a cool MOSFET heatsink whereas 500 pounds, 1000 pounds?  Something must pop, and it would be educational to find out the process by which it occurs.

I wonder whether intermitantly braking while going down steep hills is better?  I know with cars riding your brakes down a long hill really heats up the pads and calipers and isn't very good for them so they recommend moderate pressure to slow down, letting go, and then repeating as often as needed to keep the speed you want.  Perhaps cycling the braking action on an EUC for heavier riders or where lots of hill climbing and descending is needed might be something to consider?

With cars braking power fades above some tempererature, so it is important let them cool out inbetween. But imho not with an EUC - the braking power stays until the board cuts off due to overpower and cooling is quite bad. So letting the wheel dissipate the braking power continuously until the max temp is reached and then taking a break until the wheel cools down should be about the only and best solution... Braking force is proportional to the motor torque, which is proportional to the current through the mosfets. And the power dissipation in the mosfets is the square of this current. So keeping the current at a constant level leads to less power to be dissipated than "creating" peaks. Since the square of this peaks will be more in average then the square of the constant level.

One can just finetune the optimum speed for each decline if one logs the behaviour of the wheel. (regenerative braking vs. using power for braking, current needed). The dissipated power should be more or less proportional to the square of the current independently of the direction - so the (constant) speed going down a hill which uses least current is the best.

... and of course the two extremes (going very slow and very fast) are to be ruled out - imho there should exist some optimum somewhere inbetween depending on the motor efficiency, the square of the current == power dissipation curve and the firmware characteristics...

[Smoother]

@Chriull thanks for taking the time to write the above detailed, precise, and logical post.  That seems the most accurate and precise explanation of what is going on in an EUC when descending a hill; at least as I visualise it.  I just don't have the technical knowledge that you do, to state it categorically, like you have. But I've got tons of real life experience to fall back on ( pun intended).

this is what I got from your post, and this thread in general if I understand it correctly:

1. Heat is not good. Too much heat is very bad. Pop goes the board.

2. Too slow while descending, Is bad for the board, too many amps braking the wheel,  too much heat. Pop goes the board.

3. fast (may) be good for the board ( little braking, fewer amps needed to rotate wheel) but too fast could be VERY bad for the rider, if the board goes pop. Speed and a hill, ouch! Of course with the board under less strain the likelihood of a pop would be smaller, but a face plant at speed down hill FOR ANY REASON would be very bad.  But speed and hill would require huge braking amps should the need arise suddenly, and eventually it will. Pop goes the board. You'd look like a baseball player trying to slide safe, only on concrete.  Ouch!

4.  Constant speed better that speeding up and slowing down.  But not constant too slow or constant too fast, see above.  Log your amps and heat for your wheel, and your hill(s) and pick the least taxing on the board and you ( if there has to be a compromise.)

5. Stopping is bad, braking is bad, amp peak, Pop goes the board.

6. Staying still is bad, too many amps. Think, stalled motor.  How long can an electric motor stay stalled before it burns out? and that's just the coils, never mind our precious control boards.

7. EUC's either, regenerate or draw power when descending, depending on the load on the motor, and switch in response to small changes in speed, wind, hill angle, etc).  Regeneration can only produce a finite amount braking force ( less than the power of the motor) after that active application of power is used to electrically brake the wheel.The load is comprised of total vehicle weight (rider, wheel, baggage), the grade of the hill, the speed selected, changes in speed ( either from braking or accelerating), wind direction (front or behind), road surface.  ( bumpy producing more power peaks than smooth).  

Wow! Not much to think about at all! I told you riding an EUC was fun ?

man!  hills are looking really dangerous.

 

[John Eucist]

4 hours ago, Smoother said:

2. Too slow while descending, Is bad for the board, too many amps braking the wheel,  too much heat. Pop goes the board.

Wouldn't keeping a "too slow" constant speed descending be less amps (and less heat) than a higher constant speed descending?

[Cerbera]

OK, so how many amps is too much ? 

And what temperature does the board cut out at ?

I did a couple of gentle but prolonged hill tests earlier...

Here's one of them - roughly the first half is 1:5 uphill, then a bit of straight, and then <1:3 downhill for the last 6 mins or so. I weigh 55k in armour and I'm on the 67 volt 820wh MS18V3, with 90% charge.

I was watching the temperature all the time, and it never went higher than 30 degrees. Amps peaked once at just under 35 as we got to the steepest part of the uphill stretch.

I'll try and do another couple of runs in the same place over weekend. We'll call this the mid-speed run, and I'll do one where I grind really slowly up and down the hill, and another where I go at it 'hammer and tongs' only braking enough to stop the wheel running away on me. I might tether it for that one It is very annoying that wheel log didn't log today's journeys for reasons that elude me, so I only have the screenshot. Anyone know why it didn't create a file this time ?

CBR 

 

[Hunka Hunka Burning Love]

 @zlymex

Has posted some nice graphs showing the current behavior when riding up and down hills.   I wonder whether a heavier  rider weight would affect the current and heat level more.   At the same speed going down hill would doubling the rider weight increase the current and heat? 

Maybe it has a lot to do with the heat dissapation ability of the MOSFET heatsink.   A 140 lb rider might be able to ride up and down hills all day while a 240 pound rider at the same speed and hills must tax the MOSFETs more resulting in too much heat that it can't get rid off fast enough resulting in a burnout.   All that extra potential energy with more mass going up the hill must be converted to kinetic energy somehow.  I'm thinking a big byproduct must be in the form of heat. 

@ImpulseZeo9201 how many hill climbs would you say occurred right before your accident?  Were there flat areas in  between where the controller board had a chance to cool down? 

[Smoother]

4 hours ago, John Eucist said:

Wouldn't keeping a "too slow" constant speed descending be less amps (and less heat) than a higher constant speed?

Actually john. That's what I have been doing on my hill descents but mostly because if I fall I don't want a lot of speed.  And yes if the hill is quite gentle, the power needs would be low, and probably regenerative anyway.  But if the hill is steep, the amps needed to slow the wheel could be significant, depending on which other factors come into play for the rider.nbut @zlymex probably has a graph of this.

I recently got 9B metrics and did a few hill runs, but there was too much data.  I'll do individual charts for each hill climb, descent, and even sanding still on an incline to see the differences, but I won't go fast down a hill; ugly as it is, I still value  my face, where it is.  Plastic surgery via face plant is not my cup of tea.

[Chriull]

1 hour ago, Smoother said:

...

this is what I got from your post, and this thread in general if I understand it correctly:

1. Heat is not good. Too much heat is very bad. Pop goes the board.

Exactly - And some wheels seem to just cut off at a certain temperature without warning (beeps, tilt-back, etc...)!

1 hour ago, Smoother said:

2. Too slow while descending, Is bad for the board, too many amps braking the wheel,  too much heat. Pop goes the board.

I would have considered going slow as safe. Especially the mentioned 6 mph - until this thread started... ;(

Could be that by the different braking methods implemented in firmware some speeds are at some declines especially "power hungry" - to examine this further some excessive logging would be needed... Could be that this 6 mph were just a notch before the firmware would have switched to regenerative braking and by this powerwise the worst speed to drive down a decline?

Or it was just the whole history of the drive that heated up the wheel and it was just a bad coincidence that some overheat protection kicked in at this decline?

1 hour ago, Smoother said:

3. fast (may) be good for the board ( little braking, fewer amps needed to rotate wheel) but too fast could be VERY bad for the rider, if the board goes pop. Speed and a hill, ouch! Of course with the board under less strain the likelihood of a pop would be smaller, but a face plant at speed down hill FOR ANY REASON would be very bad.  But speed and hill would require huge braking amps should the need arise suddenly, and eventually it will. Pop goes the board. You'd look like a baseball player trying to slide safe, only on concrete.  Ouch!

4.  Constant speed better that speeding up and slowing down.  But not constant too slow or constant too fast, see above.  Log your amps and heat for your wheel, and your hill(s) and pick the least taxing on the board and you ( if there has to be a compromise.)

I would state the same, just not the too low speed - see my comment above.

1 hour ago, Smoother said:

5. Stopping is bad, braking is bad, amp peak, Pop goes the board.

6. Staying still is bad, too many amps. Think, stalled motor.  How long can an electric motor stay stalled before it burns out? and that's just the coils, never mind our precious control boards.

Braking is quite the worst... With some weight, speed and decline the powers needed to brake get quite huge! Imho most(?all?) wheels are already overchallenged by emergency brakes at higher speeds at level roads.
Standing still should not be a problem anymore. This was imho just in the "beginning times" of the wheels that the board fried while standing still. This should be under controll by now?

The high peaks from my logs @Hunka Hunka Burning Love mentioned where imho a short moment before stopping... At least i hope so...;)

1 hour ago, Smoother said:

7. EUC's either, regenerate or draw power when descending, depending on the load on the motor, and switch in response to small changes in speed, wind, hill angle, etc).  Regeneration can only produce a finite amount braking force ( less than the power of the motor) after that active application of power is used to electrically brake the wheel.The load is comprised of total vehicle weight (rider, wheel, baggage), the grade of the hill, the speed selected, changes in speed ( either from braking or accelerating), wind direction (front or behind), road surface.  ( bumpy producing more power peaks than smooth).  

Regenerative breaking can be very effective. Imho the max is possible at high speed with quite empty batteries.

At high speed with full batteries no or almost no braking is possible - there imho the firmware also does not switch to "active braking". The wheel just cuts out (or tilts-back before cutting out...). There are quite some threads regarding this "accident cause" active around here. Could be that active application of power to brake at high speed is way too power consuming for the board?

Below some threshold of speed  regenerative breaking is not possible anymore (generated voltage too low to charge the battery) - since all wheels can  brake until standstill there has to be an "active power consuming" braking mode...

[Smoother]

Quote @Chriull. 

"At high speed with full batteries no or almost no braking is possible - there imho the firmware also does not switch to "active braking". The wheel just cuts out (or tilts-back before cutting out...). There are quite some threads regarding this "accident cause" active around here. Could be that active application of power to brake at high speed is way too power consuming for the board?

Below some threshold of speed  regenerative breaking is not possible anymore (generated voltage too low to charge the battery) - since all wheels can  brake until standstill there has to be an "active power consuming" braking mode..."

 

i find these statements quite thought provoking. On the one hand, regenerative braking is accepted as a fact, and on the other hand, at close to zero wheel speed, no effective regenerative braking is possible, so active braking, through the application of reverse power to the motor, slows the wheel to a stop.  So a transition  from regenerative braking to active braking HAS to happen on occasions when deceleration starts with regenerative braking but continues to a full stop. Right?  But if the board is hot, either form of power, created by battery or wheel, adds even more heat.

So why did OP eat it at 6mph? He wasn't accelerating, he wasn't braking. He was maintaining a sensible controlled speed.  Heat from consecutive hill ascents and descents? Too many amps to maintain this relatively slow speed ( akin to riding the brakes,) producing amps, and heat? Or both?  There is no doubt, that the longer the ride, the hotter the board.  And the more hills you ride in either direction, the hotter still the board.

 That's it, I'm taking a hack saw to my wheel to open up that board to the wind ( not really) would solve a lot of this stuff though.

[Flash]

1 hour ago, Smoother said:

Quote @Chriull. 

"At high speed with full batteries no or almost no braking is possible - there imho the firmware also does not switch to "active braking". The wheel just cuts out (or tilts-back before cutting out...). There are quite some threads regarding this "accident cause" active around here. Could be that active application of power to brake at high speed is way too power consuming for the board?

Below some threshold of speed  regenerative breaking is not possible anymore (generated voltage too low to charge the battery) - since all wheels can  brake until standstill there has to be an "active power consuming" braking mode..."

 

i find these statements quite thought provoking. On the one hand, regenerative braking is accepted as a fact, and on the other hand, at close to zero wheel speed, no effective regenerative braking is possible, so active braking, through the application of reverse power to the motor, slows the wheel to a stop.  So a transition  from regenerative braking to active braking HAS to happen on occasions when deceleration starts with regenerative braking but continues to a full stop. Right?  But if the board is hot, either form of power, created by battery or wheel, adds even more heat.

So why did OP eat it at 6mph? He wasn't accelerating, he wasn't braking. He was maintaining a sensible controlled speed.  Heat from consecutive hill ascents and descents? Too many amps to maintain this relatively slow speed ( akin to riding the brakes,) producing amps, and heat? Or both?  There is no doubt, that the longer the ride, the hotter the board.  And the more hills you ride in either direction, the hotter still the board.

 That's it, I'm taking a hack saw to my wheel to open up that board to the wind ( not really) would solve a lot of this stuff though.

hack saw ?   chain saw ? 

Chain saw

[Chriull]

2 hours ago, Smoother said:

So why did OP eat it at 6mph? He wasn't accelerating, he wasn't braking. He was maintaining a sensible controlled speed.

Going down a decline and maintaining a constant speed implies braking!

And the balancing of the wheel to keep the rider upright standing is additionally a continous accelerating/braking.

2 hours ago, Smoother said:

 Heat from consecutive hill ascents and descents?

Could be, that the temp was already quite high before he started the descend?

Once we get more logs from comparable MV3 rides we'll know maybe a bit more...

2 hours ago, Smoother said:

 That's it, I'm taking a hack saw to my wheel to open up that board to the wind ( not really) would solve a lot of this stuff though.

A heatsink mod ( as i.e EUC Extreme has made) is for sure helpfull. But also it sounds quite plausible, we can't be sure that this accident was caused by overheating...

[Smoother]

1 hour ago, FLASH said:

hack saw ?   chain saw ? 

Chain saw

Wow! That's a great picture.  I'm half tempted to replace my current picture with it. brilliant.

 

11 minutes ago, Chriull said:

Going down a decline and maintaining a constant speed implies braking!

Sorry, yes I know that.  What I thought I was saying was : he wasn't slowing down, and therefore not calling for an additional amp spike, other than the amps his steady constant decent was already using.  But I thought wrong.  Sometimes these reports can seem wordy, but it is necessary in order to convey exactly what one means.  In this case I failed. Mia culpa ?

 

On on a different note.  Do you think we should split this thread.  We seem to have hijacked the OP s crash and injury report, making light of his severe injuries, and accompanying pain.  No one should have to endure that.  The pain I mean, not the hijacking.

[Keith]

2 hours ago, FLASH said:

Below some threshold of speed  regenerative breaking is not possible anymore (generated voltage too low to charge the battery) - since all wheels can  brake until standstill there has to be an "active power consuming" braking mode..."

 

This comes up at regular intervals, but, as Scotty said:" Ye canna break the laws o' physics Captain!". Short circuit the coils of an electric motor and it will become very difficult to turn, force it to turn anyway and you will generate a current flowing though those coils which will be converted to heat (simple conservation of energy https://en.m.wikipedia.org/wiki/Conservation_of_energy ) that is, effectively how you can brake an electric motor, but that energy has to go somewhere, so instead of shorting the coils they are reversed to the battery by turning on the correct MOSFET's at the correct time.

The network of MOSFET's are connected to the three windings of BLDC motor we use such that a pair (or group of pairs) can connect a coil end to either battery positive or battery negative, that is why there are 6, or some multiple of 6, MOSFET's.

So three possible states exist for each of those 3 coils:

• Off
• Connect to battery positive
• Connect to battery Negative

The software needs to ensure that if one end of any coil is positive, the other end is off or negative, connecting both ends to positive or both ends to negative at the same time is a full short through the MOSFET's, great for braking but might blow the MOSFET's quite quickly as current could be very high) it is exactly what we do to stop the propeller on R.C. Electric planes though, but it is very small amount of energy for a very short time.)

So, regardless of the speed the wheel is turning (and you need to remember that there are a great number of pole pairs on these motors so the RPM, or correctly the a.c. cycles, the electronics is experiencing is the wheel RPM multiplied by the number of pole pairs) power is flowing into the battery, if at any point power flows out of the battery whilst leaning back, the wheel has to be physically going backwards.

I guess it is just about possible the software might switch the MOSFET's in such a way that they short the coils once back e.m.f. has reduced below a certain level and rely on the heat being dissipated through the motor windings, but that risks overheating the motor and possibly over current the MOSFET's so I'm not at all convinced any of the controllers are that sophisticated?

The below image from rcgroups.org

[Smoother]

Thanks Keith, I knew if I threw out enough pseudo pscience, someone would be compelled to whip out the real stuff so I wouldn't have to.  Now you've done the research, I can build my own monster motor and spin the earth backwards. Humm, let's see, delta or star? Decisions decisions.