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Being thrown off my bot..


Adamski

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Hi guys,

I bought my E+ from Project 42 three months ago and am loving it!!!

I must say, the only times I've come off have been when the battery has been low and the bot has decided to 'throw me off' (I'm 72 kilos)... this has happened at quite high speed. Once uphill and twice downhill (hoofing it!) when the foot plates start to lean upwards. I was aware of this function so wasn't surprised, but luckily I haven't 'faceplanted' yet. I wear no protection whatsoever (which I know is not wise), but I have found that when I'm thrown off, I just carry on travelling vertically and I find myself automatically running at high speed...with the bot spinning and beeping in a pile behind me. This has happened 3 times and am wondering if anyone else has been ejected off their bot and not 'faceplanted' in a similar manner.

I know I'm going to get a lot of stick from you guys for not wearing any protection....and I know this might sound strange....but it actually doesn't feel that bad being thrown off.

But maybe I've just been lucky...I certainly don't want it happening too often.

I have found that my bot shouldn't really be ridden with only 20% battery left. Oddly enough, it's fine if I'm riding it from 100% all the way down to say 10%, it is quite stable.

If, however, I ride it to about 25%, turn it off, then a couple of hours later try to ride it again without charging it back up....it's generally a bad idea. It'll go from 25% right down to 10% within about 15 mins. This is compounded by the cold weather.

Anyway, I'd be interested to hear from any fellow botters who have suddenly found themselves Linford Christie'ing along the pavement with no ill effects.

Also, has anyone noticed the same bot behaviour in regards to battery percentage?

Cheers,

Adamski

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When you say 'Vertically' I'm pretty sure you mean 'Horizontally' - yes, I've had that experience ;) but only when the main board failed - never during 'normal' operations even when pushing the limits, maybe I'm just not trying hard enough?

Would be great to see somebody 'ejected' vertically, but only for comical value of course :P

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@Adamski,

Safety, has been discussed in detail so I won't repeat here - you're either very skilled or very lucky - I wonder which ?

A number of riders have previously commented that wheels appear to be a lot less safe to push hard if the battery is low. That does make sense when you think about it. Cold weather will definitely not help.

This graph which I've borrowed from: http://www.ibt-power.com/Battery_packs/Li_Polymer/Lithium_polymer_tech.html (I hope they don't mind) demonstrates a couple of points:

The remaining capacity display on a wheel is nothing more than a voltage monitor. The graph shows you:

a) voltage drop is pretty much exponential; below 25%, voltage drop is rapid, how well your wheel's capacity monitor scales that change is questionable. Additionally, a rested battery's voltage recovers somewhat, potentially giving a false higher capacity reading.

b:) lower temperature, lowers capacity and voltage significantly, If you start at 25% in a warm room and ride out into the cold, a big drop in capacity will be seen as the battery gets colder.

Another characteristic, not so obvious in the graph, is that both colder conditions and lower voltage increase the internal resistance of the pack, dropping the voltage further and restricting the current that can be supplied to the wheel (although this will help warm the pack a bit ?).

So, low capacity will reduce both voltage and current availability, colder conditions will make it worst. Your wheel's power will be dramatically reduced, increased speed then greatly reduces the reserve power available  to keep you upright. Additionally voltage drop can then be rapid and sudden. All of the above might fool even the best of EUC's safety features, The wheel may cut faster than it can warn by tilting back or simply power may be too low to hold you upright if you lean forward.

It has been said before in several posts: 

Don't push your EUC's top speed if power is low (80% is considered a good safe figure by those with more experience than I)

Charge and go! Drawing that last 20% out of your battery significantly damages cycle life and capacity and is best done as infrequently as possible.

 

image.jpeg

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1 hour ago, DangerousDick said:

When you say 'Vertically' I'm pretty sure you mean 'Horizontally'

I was thinking he was meaning Vertically and he's running it off.  If that's the case, then he's a Good Runner!  I used to be when young, but now days, I doubt I could run off a full speed spill.  And, even if I could, it only takes a small catch of the toe to change it from a Run-Off to a Slide Into Home Base.

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Hi DangerousDick!

I do mean vertically....seriously.....I fly off the bot and travel approximately two feet in the crucifix position before hitting the ground....scary stuff... I might try rein-acting it for you if you're lucky and post the vid on here ;-)

Thanks Keith for your post....very helpful that actually as it explains a lot as to where I'm going wrong with my charging expectations.

19 hours ago, SuperSport said:

I was thinking he was meaning Vertically and he's running it off.  If that's the case, then he's a Good Runner!  I used to be when young, but now days, I doubt I could run off a full speed spill.  And, even if I could, it only takes a small catch of the toe to change it from a Run-Off to a Slide Into Home Base.

Hey Super, I did used to be a quad and inline skater...I did a lot of half pipe tricks and real mad crazyness in my youth so I suppose my balance and muscle memory for faceplanting is a bit more tuned....

....you're right though...all it takes is a 'catch of the toe' and i'd have a mouth full of teeth....  

Again, thanks for your comments guys, I'll keep you posted as to my first proper faceplant....

Happy botting all  ;-)

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@DangerousDick @Adamski

If my memory of physics classes serves me right: the wheel moves horizontal, the riders jumps vertical resulting in a projection forward under a certain angle, and gravity turns this in a parabolic trajectory.

Any physics teachers present here? Now you can make classes about torque and gravity really cool, talking about a face plant with an EUC. Yes!!! :D

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Yo Jurgen,

Yeah man, I was definitely moving away from the source of the motion so, if my days of revetting physics classes serve me correctly, I was in what is classed as an escape orbit or C3 = 0  orbit.

Bakers equation explains this quite well:  t-T={\frac {1}{2}}{\sqrt {\frac {p^{3}}{\mu }}}\left(D+{\frac {1}{3}}D^{3}\right)  - Faceplant 1.01

 

although I prefer Keplers: 

A={\frac {3}{2}}{\sqrt {\frac {\mu }{2r_{p}^{3}}}}(t-T)

B={\sqrt[{3}]{A+{\sqrt {A^{2}+1}}}}

then

\nu =2\arctan(B-1/B)  - Faceplant 1.02

 

Which one do you prefer?

 

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7 hours ago, Adamski said:

Yo Jurgen,

Yeah man, I was definitely moving away from the source of the motion so, if my days of revetting physics classes serve me correctly, I was in what is classed as an escape orbit or C3 = 0  orbit.

Bakers equation explains this quite well:  t-T={\frac {1}{2}}{\sqrt {\frac {p^{3}}{\mu }}}\left(D+{\frac {1}{3}}D^{3}\right)  - Faceplant 1.01

 

although I prefer Keplers: 

A={\frac {3}{2}}{\sqrt {\frac {\mu }{2r_{p}^{3}}}}(t-T)

B={\sqrt[{3}]{A+{\sqrt {A^{2}+1}}}}

then

\nu =2\arctan(B-1/B)  - Faceplant 1.02

 

Which one do you prefer?

 

Well Baker seems interesting: let's say you travel at 20KmH, and you jump up with an acceleration of 19,62 m/s2, you're 1,78m tall, after how many seconds would your face hit the ground?:unsure:

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3 hours ago, Jurgen said:

don't try to drag her to your cave by her hair, there's something new called 'wiggs' nowadays:ph34r:

Hehe, Dang Weaves!  I walked 1/4 mile before I realized I only had her hair and she was still back at the Caveman Bar.

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