I’ve been asked by a friend for a solution to a problem he and his friends have.
They do long downhill runs (cable cars to the top first) in Montana but want to start with fully charged packs become sometimes they stop partway down to cruise around before continuing the rest of the run down.
These downhill runs can be several kilometers long and they’ve had some fried ESC’s and are worried about pack longevity when being over overvolted due to the regen braking current. They don’t want to start with partially charged packs since they might stop and cruise around a bit at any point.
They asked me about rheostatic/dynamic/regenerative braking modules. Perhaps sharing regen current with the pack (dissipating it as heat for the entire braking time) but definitely kicking in at a certain voltage level to divert current away from the ESC+pack during downhill braking.
Any commercially great solutions out there? Or all they all just a bit of circuitry and a FET allowing current to flow through some resistors at a certain voltage? If nothing good is available then I’ll put something together for them but that will take a while.
I don’t know what ESC’s they are using or whether any support direct use of resistors. Assume they’ll need an external standalone module.
I realize that any solution can only be good for up to a certain point.
I wonder if what they sacrifice in space for a big resistor could be used for extra cells in the pack affording them some uncharged space in the pack to brake.
also, I feel like disc brakes are better at turning kinetic energy into heat.
and backup disk brakes is kinda cool to have.
Mooch’s friends are going downhill, really fast.
Full battery.
Might cause problems.
And to solve that problem you want to hook up mechanical brakes to the vesc so when there is a fault caused by going so fucking fast down a big hill,the brakes will lock up and pull the board out from under their feet faster than I pull out of my GF when she says “put a baby in me”?
Is that the plan here?
@Battery_Mooch I would watch out for this guy, I think he has it in for your friends hahaha
My 2 cents, a rheostatic brake or brake chopper (that’s what people call it in other fields) is something that should be mainstream, basically you derivate a Zener diode and fat LEDs or fat resistors between your battery and ESC and you’re up.
Short story The zener will suck any extra unwanted voltage above breakdown level, and the LEDs/resistors will burn the extra watts your setup cannot support till you come back to your normal max battery voltage.
It doesn’t take that much space, doesn’t fail easily (under normal conditions it remains idle) and provide an extra layer of safety that no “more cells” will compensate (you are limited by your ESC spec and your battery pack max voltage, no matter how many P count you add).
It’s not redundant to mechanical brakes because unless you give up 100% regenerative brake, you can still overload your battery & esc when full charge + long downhill braking, even with mechanical brakes.
@City-Blade-101 gave me a Maytech unit so I could see how that thing is made inside and how to scale it for various voltage levels, it’s relatively straight forward TBH!
So @Battery_Mooch you might want talk your friends into making one for their batteries, cheap to make & definitely worth it!
What kind of wheels are they using? In case of pneumatic there would be room for a disc break.
I think it would be possible to add an arduino between the remote and the esc, the arduino would read the battery charge level from esc through uart, if its below the threshold it would just mirror the control command, if its above it would trigger some stepper that would pull the disc break bowden.
On the other hand this is kind of recipe for disaster to have two braking system on a board which could behave differently
There’s a tiny problem with that…
If we’re shunting, let’s say, 20A away from the pack through a zener conducting fully at 50V then the zener needs to dissipate 1000W of heat. It will work for perhaps microseconds before that zener turns into a ball of incandescent gas.
If we use series resistors to limit the current through the zener so it only needs to handle a couple watts of heat then we’re only diverting about 40mA of current from the battery.
We can easily get resistors to handle that 1000W of heat for a bit but that’s a lot of LEDs.
A particular voltage-rated zener conducts to varying degrees over a wide range of voltages too. That would also need to be taken into account.
These things always freaked me out. I dont personally think I would be able to deploy them safely in a situation where I need emergency brakes. By having to shift my foot over the pedal, I would be transferring my weight to my back foot, which could induce wobbles. Then once my foot is over the pedal, I doubt I would have the control in my foot to avoid slamming down on the brakes full force.
Maybe if they were placed in a way where I didnt have to lift my foot, just pivot and raise my toe over the pedal. Not sure. I am also a shitty skater, so dont listen to me lol.
Hmm…perhaps a wireless bite-activated brake trigger would be just the thing? We’re probably clenching our teeth anyway if we think we’re about to crash. Why not put that reflex to use?
Yes, downhill. But not very fast as they are just cruising (hence, lots of braking) and taking in the sights and there is the ever-present worry of a huge logging truck taking up most of the road around any bend.
I’ve come close to splatting on a couple myself when biking out there.
Great point. In my experience, the drivetrain resistance is usually enough to keep me from endlessly accelerating, even on fairly steep hills without any brakes applied.
I’ll ask them about this. Though I can’t imagine they would come to me if they were going slow enough. Perhaps the free-running speeds are still too fast for them.
Oh yeah, dont get me wrong, my free-rolling speed down a decent hill was still much faster than I wanted to be going haha. Probably a bit faster than my board’s top speed of 35mph.
I was just saying to Al’s point that we have a fairly high resistance drivetrain that keeps us from endlessly accelerating like on an analog longboard.
