Plenty of threads around with people haveing issues with braking on 63mm motors which boils down to an ABS overcurrent fault. I personally still use version 4.12 on 63mm motors but I keep my ERPM well within spec and I also run very low braking current to avoid this. I originally used sk3 motors that have a smaller stator diameter than maytech/tacon and rarely had any issues, if at all. It wasn’t until I started pushing my systems with larger stator motors that I began to see problems and realized a direct correlation in stability and motor size.
It is common knowledge within the RC world that you run motors that do not exceed the max current rating of your ESC. You do this so you do not overheat your motor controller and fry your hardware. Using a motor that falls below the max current rating of your ESC allows you to drive the motor hard without triggering the overheating safety cutoff and allows you to climb hills that would normally cause the VESC to overheat and reduce power. Finding a balance and having headroom in the correct places within your system is key to good design. Sticking large motors on an esc that cannot handle them at WOT is poor design but will work if you make enough concessions.
Here is a quick search result for the words “R-SPEC” & “VESC”
There are at least 50 build threads published on this forum alone with this combination of R-SPEC 63mm motors & VESC… also there are other suppliers of 63mm motors, e.g. DIY & Alien…
Not to mention all Raptors & LHB builds use 63mm motors & VESC
There just isn’t any concrete evidence of stability issues due to 63mm motor Stator Diameter.
The VESC issues are most likely related to the very sensitive DRV8302 Chip & User Error/bad settings, hence the reason Vedder has dropped it from V6.0
The problem is Chaka won’t admit that some of his VESC have failed for no apparent reason… He simply chooses to tell everyone that its a 63mm motor problem as this shifts the blame to someone else. Its a great strategy & It would appear many people are believers!!
The problem I see with this marketing strategy is that Chaka will probably want to sell 63mm motors at some point in the future, then his language will have to change. Potters Prophecies!
A bit anecdotal, but @Photorph ran into an issue with a LHB board where his brakes cut out and he had to slide on his knees pads to stop. Nothing conclusively saying big motors are problematic, but i thought I’d point it out. It’d be nice to have some scientific resource for these kinds of tests.
The larger 63mm motors are probably more efficient during regen and therefore pushes more current back through the vesc. A dual motor configuration should reduce this problem by half for the same amount of braking power.
I’ve had issues with braking and my LHB build and posted videos in the build thread - I also updated settings from forum advice with LHB’s advice. The issue was mitigated but didn’t completely go away. Not sure what the issue is - must be user error.
The issue seems to be caused by the initial burst of current when you apply brakes at speed. A dual configuration reduces the load but you can still induce this burst of regen current if you apply the brakes hard.
If it is a transient effect my gut feel would be inductance between the battery and VESC. Long wires/thin wires/bad connections between these two could cause a proportional voltage burst on the VESC side when current is flowing towards the battery. If this is the case the problem should be less likely to occur at the end of the ride when the battery has been drained (The sum of the battery voltage and the spike might, in this case, be lower than the threshold causing the release). Telemetry would be awesome. Will see if I can build a small SD card logger some time in the future for some offline logging (using some off the shelf Arduino parts).
@Kaly I leave my ERPM at the defualt setting and only adjust the braking current if the battery or BMS cannot handle the regen current. Take into account that I control my ERPM with motor selection keeping it below 60k. If you are getting a fault during braking you can adjust the braking current but it does not completely solve the problem.
@Lizardking0069 BLDC motors are in a constant state of regen while spinning, even while being powered, not something that can just be turned off. I try not to expend too much time finding workarounds to problems caused by an unbalanced design. One thing a lot of people do not account for is the fact that motors pull power. The VESC can throttle this to a certain degree but we still see spikes in current. This also applies to regen.
One thing our resident fortune teller has right is that we will be bringing a 63mm motor to the market but we are waiting for version 6.0-6.1 VESC. No sense using huge motors if you can’t supply them with the current they need or pull.
If you are power hungry and you can’t wait for V6 then you are better off using a high quality car esc that can handle the amp draw. You lose the smooth throttle response of the VESC but the system will handle the load.
@chaka Thanks! Your explanations make very good sense. It is what it is and I think you laid all of that out very clearly. This information is very much appreciated.
Vedder posted some updates for everyone on his forum today.
What is implemented, tested and working so far:
The built in NRF, which can be used simultaneously with other applications
DRV8301 configuration. I need to update the code a bit to report the faults read from the SPI bus though, but so far I didn’t have any DRV faults at all, so implementing this didn’t have so high priority.
Current sampling using all three shunts for the best possible samples (I have tested using low side samples, high side samples, combining them, and combining low/high side samples with just two shunts).
CAN-bus with the new transceiver.
Motor parameter detection works fine with these amps as well. Inductance measurement is more consistent and accurate now since I take advantage of having three shunts.
Both BLDC and FOC are updated and take advantage of three shunts.
I have fixed bugs in the firmware here and there while refactoring everything. Most notably will probably be the current control fixes when brake and acceleration currents are different.
The old hardware is still fully supported in the firmware.
Here are few other important details that have left me speechles!
In general, this hardware seems to be significantly more robust than v4.x, most likely due to the layout of the new power stage where all traces are short and both ceramic and electrolytic caps are close. Some interesting test I made:
A 6-pole 0.6µH inrunner. This motor would always kill the DRV within a second or two on the old hardware, especially when running FOC since the inductance and resistance is so low (0.6µH is just evil). No problems at all so far, not even on FOC. I could run the motor up to 130K ERPM in FOC.
To test the FOC high speed performance, I tried a small high-kv inrunner at 30V and 50 KHz switching frequency. I could run it up to 230K ERPM, which is a lot higher than I expected from FOC. That means that a small ESC with FETs that are easier to drive at high speed is possible, which would be perfect for racing quads.
Even though the shunts are 0.5 mOhm now (half of 1 mOhm from before), small motors work a lot better, even on low speed. The overall performance of the current measurement is better now, so these amplifiers seem quite nice so far. I have a bunch of small motors that didn’t work before without changing the shunts, but now all the motors I have tested work on FOC.
I have a Turnigy Multistar 2216-800Kv motor with a propeller on it for my RC airplance, and it works nicely. The sensorless observer for FOC can easily track the motor through 0 speed with full torque (applying active braking before the direction change), meaning that the direction can be changed very quickly with a propeller (I will show it in a video). This is cool because it can be used for multirotors like this:
A castle 2028 (also a quite evil motor) works nice at 120A phase current with FOC without any dead DRVs. The main problem I had with RC car motors before was the current measurement because they have so low inductance, but these problems are mostly gone now. This can be a significant improvement for RC car ESCs in general, where FOC and smooth current control can be used on really difficult motors.
