I was thinking of cutting a triangle from cardboard until it fits perfectly and then measure it.
Never worked with polymer clay, don’t have it on hand and not sure I wanna mess with it. But tbh. if someone promised to make a BMS to fit if I do it I would. Even if the S was 18 or lower (meaning I may not use it myself), I’d do it for the people! 
In fairness…very few people knew about the poll. I’m pretty certain if you had a drop in replacement sized BMS for that compartment, you’d sell quite a lot. Not just to people here, but hundreds that don’t even know this forum exists. And Onewheel repair shops all around the world, especially as more people get them outside the US and can’t send them back to the US for repair. And as the Balance App code gets better suited to tuning that shape of device.
Sure, I’m partial. But I also know how OW people are. They’re pretty spendy.
But anyway, I anxiously await the 18s Lite and will likely buy several of them. So…as you were, everyone. I don’t mean to come off as a pest about it.
Sits and waits in anticipation
Well, having enough surface space, I think a 30x130 is possible for discharge too, which I would prefer for sure, before than just only charge. If I do a change on my XR, I would prefer safety first too.
Regarding the few votes in the poll, few people knows about this forum/thread except few geeks here and there… If the onewheel community knows about it, I warranty you that will be HUNDREDS straight away, I am 100% sure.
For safety first, on a Onewheel, you certainly don’t want the BMS to turn off the board under you (happened to me, so you can trust me on this 
). The VESC takes care of undervoltage, overvoltage and maximum current IIUC, but all that would cause most likely is damage to your battery (as opposed to a split second superman-style nosedive…).
Granted I think @ENNOID was talking about communicating this with the VESC over CAN when you cross these thresholds. But you need support for that in the VESC, and what does the BMS do if the VESC doesn’t listen? It adds quite a lot of logic on both sides. More logic, more potential for an error. Just me theorycrafting here though.
Charge only BMS don’t have this problem. They simply can’t cut power even if aomething goes wrong.
A full BMS can do a hard power cut when a problem is detected. This can become problematic if a problem is detected while riding. The idea to overcome this is to eventually implement a function that will do a soft shut down thougth the VESC before cutting down the power on the BMS the hard way. The VESC would also be programmed such a way that it can’t run without a ok signal from the BMS. If the CAN communication signal is lost, it would do a soft shutdown as well or simply trow an error at startup.
…continued, the FULL BMS would still be able to do a hard shut down and disconnect the pack, but at least this would only occur after the rider as stopped. It would also protect against a shorted VESC…
For safety first, on a Onewheel, you certainly don’t want the BMS to turn off the board under you (happened to me, so you can trust me on this
Just curious to know if this situation above happens on a unmodified onewheel which use a FULL BMS? I guess they would have a lot of complains if there was clear user safety issue with the use of FULL BMS…
Whats limiting the discharge in the high discharge version? The pcb current path or the mosfets?
Most power faults on an unmodified Onewheel result in a tiltback that increases in angle until the board can no longer be ridden.
There are some errors, however, that cause the motor to simply shut off. However these were mostly “incompatible hardware” errors that resulted after they revised the hardware where both the ESC and the BMS were serialized and paired. The first implementation of this led to errors, and the controller rejected the BMS and shut off. I’ve personally only seen 6 reports of that happening mid-ride, but it happened nonetheless.
Everything is pretty much balanced. Connectors, copper shunt & FETs
I’m still pretty sure that it is possible to get a FULL BMS as safe on a user perspective while being also safer on the hardware side.
People tends to discard FULL BMS option because they had bad past experiences with cheap & crappy chinese BMS. Do they do bypass BMS, uses it only for charging and say it is safer this way, but honestly this is a misconception. I’m not saying that my BMS is yet ready to make fall those misconceptions, but I’m working on this.
Thanks for the info
I would say there have been more safety issues with BMSs cutting off the battery from the motor controller than batteries getting an issue because the BMS could not decouple the battery from the motor controller. Usually a simple slow blow fuse adds enough safety against shorts of all kinds.
An ideal system would have a power switch that can be operated by the BMS. If the motor controller and the BMS are coupled via CAN, the motor controller would also be able to operate the switch.
Not the cheapest solution though…
I agree with you on the safety facts and this is one of the reason why some users tends to use charge only BMS.
Most crappy FULL BMS have back to back FETs on the low side discharge path which can damage the ESC+BMS under high current cut off due to over voltages & floating GND. Sudden braking also becomes a safety issue for the user in case of pack disconnect.There is no valid reason to use back to back FET & low side cut off on the discharge path IMO.
Using a single FET stage on the high side discharge path removes the hardware related issues. For user related issues, a FULL BMS having a solid algorithm with the ESC over CAN bus before disconnecting the pack would be a proper solution.
Reason for having a back to back solution is to have the FET switch bidirectional without leakage thu the body diode. Very common implementation. The power dissipation is twice as big as a single FET solution, but if you have space to design it then generally its a pretty robust design.
A nfet solution with a charge pump on high side is preferable.
Some regulations requires galvanic isolation however so we mostly use these really big mechanical solenoid solutions, they can handle 450A all day tho and make/breaks of a few kA.
For galvanic isolation, I’m selling master-LV & Master-HV on my website. Thise boards uses main contactors instead of FET.
Back to back FETs are indeed very common, but creates some issues. Unless you want a common charge/discharge port BMS, there is no need for this less efficient & problematic design choice… Common charge/discharge port is not a good design choice either outside of some specific case.
Hi guys, yeah I barely saw that poll my self. I don’t think it would be very representative at all. But it did show high statistical inclination towards narrower but longer shape due to better space utilisation.
Have you considered non-comunicative solution to the bms? Like It’s a rheostatic brake module - Spintend company developed for over voltage protection during regen Breaking to sell along side their dual VESC6 based UBOX 75/200 controller (in testing now)?
Or even easier, why not to code Vesc so that regenerative Breaking is reduced 0-100% for the first 0.1v per series of discharge (100% reduction at 12s 50.4v to 0% reduction at 49.2v) or even set 100% reduction when voltage gets to 4.225v per series
I don’t think there is a way to have e-brake and yet not to over charger battery, best we can do is to give warning to the driver by sensible reduction in ebreaking as limit approaches and than stop regen on controller side - no need for controller to talk to bms for that in my opinion
Much more useful would be an ability to configure bms to our needs via something like BT or have controller with BT to pass through bms so that we could connect to bms app via controller BT module - like uart pass through.
Hey… well I advertised it in the Little FOCer thread, where the Onewheelers supposedly gather. So I’d think all Onehweelers interested in this BMS would pop in to vote. I’m not too good at this though.
Yeah I calculated surface area too back than and it seems feasible
But actually important dimensions would allow for even larger one 182=36mm x 652=130mm, so that is even more surface area.
From design point of view no one will use 15s set up because it is just waisted block on battery than it would always be Even number 12s/14s/16s/ or more
Agree 12 to 18s are the most common voltages (12-16s I would even say, 18s is sort of crazy one out there)