I don’t have time to listen to all of it but not bad for the amount I heard. You definitely have a better understanding of it than I did as a student.
I’ll give a quick response here on top of @mr.shiteside’s explanation.
Correct. The STM32 can’t source/sink enough current to turn on/off the MOSFETs in a reasonable amount of time.
Correct. see answer above
The STM32 can’t do high side switching. The high side MOSFET’s source reference is the motor phase which is going between ground and battery voltage. You need at least 10V (Vgs) to fully turn on the MOSFET which means the high side mosfet is being turned on with Vbatt + 10V in relation to ground. So yeah you have to have something that can manage that i.e. gate driver w/ bootstrap.
Yes. The STM32 can only source 3.3V. Not enough to fully turn on the MOSFETs which need at least 10V at the gate to be considered fully on. Again the STM32 can only source voltage in reference to ground so it would be limited to low side switching only.
Cheers, yeah as I said I’m perfectly fine if folks don’t have 25 minutes to kill
I goofed on this part a bit, I used the threshold voltage where it starts to conduct because there was a clear number given in the datasheet. Didn’t account for the full turnon even though that was the main point
I got a 16 hour car ride tomorrow added to the queue
Very good project, any idea when it will be available?
No eta yet.
I’m back to do what I do best - ask stupid questions!
With the DRVless design, I sort of assume that means you have to design your own DRV, or at least something that buffers the switching and switches both high and low, from discreet components. Is that right? If so, will it be more robust than the DRV8301?
Is the reason to go DRVless primarily to get around the supply chain issue, or does it make a better ESC? Would this be easier to trouble-shoot if one or more of the discreet components fail?
One thing I always kind of wish the older designs (e.g. CFOC2) had was a daughter board for the DRV8301. That way, when the DRV fails, you just unplug the daughter board and risk only the daughter board when going to town with the hot air station.
The DRV chips are a sort of “all-in-one” gate driver chip. In fact the vesc basically started out as a DRV8302 development board with an STM32 processor and shunts added so it could be more precisely controlled.
The older generation includes a 60v to 5v buck converter to help run the peripherals and logic stuff using a second 5v to 3.3v converter. Coincidently they always seemed to blow a hole right where that buck converter is.
The new ones like the DRV8323RS have an adjustable buck and current sense amps all built in. They are also nearly impossible to get right now.
What most “3rd gen” vescs seem to be moving towards are independent gate drivers. Three individual gate drivers to switch the mosfets, a separate buck and separate current sense amps (on designs that need it).
I think there are some cost savings using one chip vs several, but it also locks you in to something that may not be available forever. The independent gate drivers seem to be more reliable too, as I have yet to see one fail, but time will tell.
DRVless means you have to replicate all the functions of the DRV with separate components. So the functions of gate drivers, current sense amps, and buck converter have to be figured out separately. A common way of doing this would be to use 3x half bridge gate drivers, 3x current sense amps like the INA181, and buck converters of choice to create 10V to 15V for the gate drivers and then another stage to create 5V. This is not technically “discrete” since it still involves using ICs rather than a bunch of individual resistors, caps, and transistors. All of this will be outlined in the CFOC3 schematic
Yeah the supply issues can be the primary reason although you can get better performance in my opinion. One can choose better individual components to serve all the functions that DRV used to. It also means component replacement is easier since replacing an individual half bridge driver or buck IC is easier than replacing an entire DRV.
Yeah…but going DRVless renders this mute. Now the ICs involved are easier to deal with an replace that the DRV ever was.
I just found out about the Cheap FOCer and now i read this - I’m excited! Still no ETA or rough price estimate?
Shaman is great about delivering timely updates on progress. There is a ton of releases ongoing across the many products they sell.
I’m ready to mess one or more of these up!
Hopefully they will keep me away from the Tronic 750…
Gunna be getting back to development on this soon. I’m involved in a lot of other projects that I don’t necessarily let everyone in on. Hence why eta for this is undefined
I don’t recall approving any other projects!
We’re definetly getting a MEGAGARGANTUANFOCER. I’ll send shaman an invoice for 32.83 if he decides to choose that name.
Something I always kind of wanted to do with the CFOC2, but never did, was to put together a sort of flow-chart for debugging failed units. Maybe that’s something we could do with the CFOC3. Maybe a CFOC3 wiki?
Yeah I’m down for any of kind of supporting documentation. That’s the stuff I can never find time for
Put together another prototype since I pretty much trashed the first one doing all kinds of surgery to it.
Works decent but need to tune the gate drive a bit more. Mosfet turnoff is just a tad too aggressive.
While I could do all of these bodges to the rest of the prototypes, I think I need to go ahead do another run. I’d rather not give beta testers anything too janky.
Figure 1. MOSFET Turnoff at 75A. 60V battery
Figure 2. MOSFET Turnon at 75A. 60V battery
Tuned the gate drive stuff a bit better and now get appropriate overshoot. There’s always gunna be some amount of it and that’s why you spec MOSFETs with a voltage rating about 25% above your operating voltage. These MOSFETs are 100V rated.
In the turnoff waveform, you see a spike up to about 68V which is an 8V spike. That’s just fine imo. I like anything less than +10V for up to the max rated motor phase current.
I did up 100A with success. I don’t want to go higher until I have round 2 of these prototypes. But things are looking really good!
I have no idea why, but I’m definitely gonna have to build a couple of these.