Can i roll faster than my board goes? please help

ESK8 Electronics
1

Can my free roll speed exceed the max speed i get from my battery…? 9s x 170kv only gets me like 35km top. Basically i wanna know if its ok to roll faster down hills with it?

I have a vesc 4 running 9s thru a 170kv 6374.

Thanks

2

Ive noticed braking comes on real sudden. But other than that it seems to be ok?

3

Belt drive can’t roll faster due to belt drag.

5

IIRC There’s also the risk to generate higher voltage from your motor than your battery’s nominal which, if you don’t have a brake chopper installed by any means, will fuck everything up (including a chance to fuck you up too).

You can check with a calculator your absolute max (no load).

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6

I’ve seen some boosted guys hit 34mph down hill I guess they didnt touch the throttle or brakes till they were in range. Honestly seems very sketchy.

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8

Shameless pitch for @hyperIon1’s rheostatic brake. I have it installed with no issue. I haven’t pushed it on a lengthy downhill run on full charge but I do unplug, roll down my driveway and a quarter mile stretch, and have no issue.

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9

So for these types of situations is it best to just brake slow when u start the downhill roll?

10

Correct

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11

woah woah this is super important and awesome. How the heck do I calculate this???

Would a high gear ratio equate to more or less back voltage…? (probably more? :man_shrugging:)

13

merci mr deckoz

14

You run mostly at nominal but your battery’s max tolerance is top voltage. Transient voltages spikes go high easily even at normal levels (that’s how most people here burned their DRV).

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15

I did the calculations with my normal top speed and all that jazz, is this right? I can smash the breaks at regular operation speed and not worry about absurd voltage spikes?

image

E: my top speed is subject to change in the future, as I want to try a high ratio with smaller pneumatic wheels… I plan on moving up to the 8 inchers when I tire(heh) of burnouts :smiley:

E2: 35mph takes me to 53V, interesting :man_shrugging:

16

The ESC is also a three-phase full bridge rectifier (thanks to the MOSFET body diodes); you will feel braking torque (equal to your acceleration) kick in at your boards max speed (+ ~1.4V), meaning you cannot exceed the max speed of your battery+motor+gearing by very much because the motor acts as a generator and the ESC rectifies the BEMF and sends current back into the battery. If you attempt to brake while this is happening, you might run into overvoltage conditions and possibly overcurrent conditions. It is best to avoid these conditions, as at higher speeds, more power needs to be returned into the battey.

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17

Got a link for that thing ?

18

Of course https://www.hyperionesk8.com/products/rheostatic-brake-dynamic-brake-for-escs

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19

Thank you :heart:

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20

Tell that to my 45kmph dh dude aha. My setup only gets me 37kmph… tops!

Thanks for trying tho i guess…

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21

Ok man thats great but will it harm the esc doing this? I have no dramas slowing down manually before hitting the brakes.

22

What if u just slowed the regen rate right down. I know it would effect braking but it would protect the battery for sure

23

Where would you wire that? Before the ESC? Is it just an array of capacitors? I want to know how it works lol