I was designing and prototyping this kind of a switch for some time now. I finally have a working design and prototype.
The basic operation will be that you just connect this between your battery/BMS and your ESC. Two small wires to your motor phases (I will provide a tutorial) on your VESC (or other ESC) or on your connectors, depending on what is easier for you.
Now you can just push off on your board once and the power will turn on. It will be in complete OFF state just like any other power switch out there today so it will not drain your battery if you dont disconnect it (Of course it takes some current for the motor rotation sensing but it is very small).
Connecting a regular pushbutton or even a momentary switch will be possible if you would like to for example disabled the push to start feature. The switch has a small MCU on board so we could even set up the push to start feature in such a way that to turn the board off, user interaction would be necessary to prevent the board from turning off unintentionally.
Now I am trying to figure out some things and that is where your feedback and ideas come in. Since I am designing this from the ground up I would like to know what you think and make this as great as it can be
My question right now is, how much time would you like the board to remain ON after the motor stops rotating/you stop riding?
Yes, it does. When the board is off you can just step on your board, push off (like on a regular longboard/skateboard) and that will turn the board ON.
This shouldn’t even be programmed in, mechanical unlatching via push button ONLY. As any type of auto-off is a safety concern if you are specifically using BEMF voltage as your data source.
THE ONLY way I would include an auto off is if your device was also a UART device of the VESC, and measuring eRPM telemetry.
This should be cool, but please take my suggestion for auto off seriously, I’m sure you can find many of my view points on safety.
The switch will be sensing motor rotation so I think that as long as the motor is rotating (under power or just rolling down hill) the switch should not turn off, after the motor stops the switch could turn off after say 5 minutes or so.
I know that some of the ESCs out there have such a feature, does anyone know how the turning off is done there? I have not used one of those yet myself.
The switch will not be prompting the VESC to boot via UART or anything like that, that would need some stand by current which is something I tried to avoid. The switch will sense the motor rotation from two of the phase wires and will keep everything connected after the switch (ESCs, lights etc.) completely off. It will turn on as if you pushed a button on a regular switch once the motor starts rotating and generates voltage on the coils/phase wires.
I think this idea is great, and actually way safer than traditional push-button as it means the board will always be forced ON whenever running. In case the board turns OFF while waiting at a red light in traffic, you would just need to push to start, way faster than having to find your push-button and start accelerating!
Also why would you need a MCU? It should be possible to activate the FETs using bemf of the motor… And using some caps to act as a time delay to turn the board off.
Thank you, yes that would be possible. I thought of just using comparator to sense the rotation. But using an MCU gives me/us more freedom in terms of what we can do.
I feel like that is not the best way to go. I think that not a lot of people would use it but everyone would have to pay for it since it would increase the price. I think that using a stand alone module if you need 12V output is a better option, sorry.
Interesting use case. If the board shuts off and then turns back on, you’ll have to wait a few seconds for the remote to rebind. Not a terrible scenario when you know the board is off and you’re starting it up, but can be annoyingly awkward when you think it’s still on, start pushing and there’s no response from the remote, or the throttle kicks in at a level that you’re not expecting it to.
That is true, that is partially why I agree that turning the board off will require user intervention is a pretty good idea. After all, when you want to turn the board off it is not that big of a deal to reach down and press a button. But being able to just push off on the board to turn it on is a useful feature.
I am with @Deckoz on this. No automatic off. I am in city riding where there are definitely scenarios where I am still for a couple minutes. Like @mikenyc said, it would be annoying/confusing delay with the remote .
Also if using a nano x, you are now uncaliberated… bad things could happen.
Maybe a minimum limit of 10 mins? If your standing completely still for more than 7 mins, especially in the city , you might as well pick up your Board and walk .
Edit: or maybe 30? That way it simply acts like a 2nd measure to ensure that the board isn’t on all night
Yeah, if it is present at all it should be a longer amount of time than a ridiculously long red light. But imagine using a nano x (one of the most common remotes).
If there is only the automatic off and not a switch for the “fully off” you would have to wait for your board to power off again, then calibrate your nano x, then push start to go again… sounds… irritating to say the least.
Okay so the way I see it now, I added a trim pot to the PCB as well as jumper pads to choose if you want to use a pushbutton too or not. So each user will be able to switch back and forth depending on what you prefer as well as choosing the amount of time it takes to turn off.
