That makes a ton of sense, if I were you I would make a post about it on the vesc forum
Correct me if I’m understanding it wrong, but let’s say at low speed the VESC is reading 60 A as phase current, but the real current is less than that, and part of the reading is due to cross talk? And by that the energy reading is also wrong since it come from the current
It should be pretty easy to test, just use a current clamp on one of the phases, unfortunately I don’t have one working to test
Another way to test would be to use the open loop command with the same current, one time with a really low ERPM and another with it higher and monitor the motor temperature
So there are three current values in question, What the phase current would be if there were NO BEMF, the actual phase current, and then the phase current measured by the VESC.
Let’s say, without BEMF, the phase current would be 82A, but because there is BEMF, the real value is 80A. However, because of cross-talk from the power stage, the VESC measures, let’s say 78A.
A similar situation is occurring on all three phases, the measured value may be higher than the actual or lower. The VESC determines the BEMF based off the predicted value (the first value, what current would be with NO BEMF) and the measured value, and since the measured value is off from the actual value, this causes the BEMF the VESC estimates to be incorrect. The end result is, because of the way motor control theory works, is the estimated rotor angle is incorrect by up to plus or minus 90°. Normally it’s not as bad as plus or minus 90° (it’s some value in between 0-90°, usually closer to 0, and gets closer to 0 as the motor speeds up) except in the extreme case that the VESC actually ends up locking onto the cross-talk signal instead of the actual motor BEMF. I actually have this happen on a prototype VESC I am working on.
The issue with testing this, is at low speeds, the three different current values in question are VERY close to each other, and I do not think clamp meters will be accurate enough.
A proper test would be creating probe points of the kelvin connections to the current shunts and probing that on an oscilloscope and comparing that to the outputs of the current sense amplifiers, also accessed using probe points.
Now I get it, it’s not that the noise increases the measured current is lower, but that it tracks the own voltage instead of the BEMF and the phases phase ends up being wrong
I just see one flaw, or maybe again I didn’t understood. At low speed it’s running sensored, shouldn’t this be a non issue since it’s not depending of tracking the BEMF? If that was the case the torque should start strong, drops when it switch to sensorless and improve as it speeds up
The VESC’s speed estimators and sensored to sensorless switchover algorithm SUCKS.
There are so many things wrong with it, don’t even get me started.
It boils down to, the sensored speed estimator sucks, and when it transitions to sensorless, it’s a very ABRUPT and hard switchover, which causes other issues. Sensors lag behind the motor position due to magnetic hysteresis, and this only gets worse as speed increases. When the switchover happens, the rotor angle that the VESC is using to generate the sine waves changes very abrupty and by a large amount. This results in loss of tracking at very high currents, or an abs overcurrent fault if the difference is large enough.
The solution is purely in firmware, second order speed estimators in sensored mode, and when attempting a sensorless transition, run BOTH speed estimators simultaneously, and do the switch only when the estimators agree on speed plus or minus some tolerance. As for the angle difference, Make the switch gradual, by using a rotor angle that is between the two, and gets progressively closer to the sensorless value.
After all the drama about getting a mountain board or not, and in the end coming to the conclusion I will get one, I have work to do here first
The thing is, for the mountain board become a reality I will have to take apart my Hummie build, but I also need to have a board I can take everywhere and it’s not bulky, to be honest the Hummie one is bulky enough I lots of times I leave it it home instead of riding wherever I’m going
So I ordered the cheapest 6355 motors that were sensored, ideally I wanted to go to a lower Kv, but the price difference was too big, ended up paying $27 each 6355 180Kv motor, they will be taken apart and converted to a direct drive
Now I’m on the fence about what VESC to get, the Maker X dual 4.12 looks good and is really compact, but if one side dies I have to replace everything, I may get two flipsky 4.12, you can find them for less than $50 on AliExpress
Procrastinating in Ali express I just found a sale of Mini FSESC4.2, got two for $98 with shipping, there is a chance that they are old stock and have the cut out problem, but then its just a matter of swapping the resistors
Torque is awesome. There is no hill I can’t climb. Make sure to change the sensorless erpm, under settings->foc-> hall sensors, to 4000 min for good torque. Because when it’s set to a low numbers say 1000 then it uses sensorless mode just after starting which doesn’t know the magnet position accurately and hence is inefficient i.e. can’t produce enough torque and motor heats up more than it should.
Starting to work on the direct drive, all is just a place holder until I have the real motor in hand, the current measurements are from a old TB 6355 that looks just like the ones I will use
I managed to get it really compact and close to the wheel, I still want to try to flip the can so I can save even more space
The Paris truck is also just a place holder, I will mill a custom one using just the base plate
The initial plan was to have a key both inside the hanger and in the stator spacer, but I’m leaning in locking the stator spacer directly to the hanger
The bulk of the design is done, now I have to wait for the sacrificial motors to arrive to adjust the dimensions
For all fixtures I will be using retaining fluid, after reading a few guides from Loctite it should work, and by having no notches on the axle the stress concentration greatly diminishes, only place that there will be something is a pin between the stator and base, that is, if the motors I ordered have a notch already made
The hanger itself (body+axle) weights 342 g, so in the end it will probably be lighter that a dual 6355 belt setup
Looks really good Pedro! I want to try some tiny 4265 APS motors with a 1:3 gear drive coupled to 76mm wheels on my travel board (lightness is also the main goal)
That will look really cool. I gave up on small motors after my 5055’s, no matter how low you set the current they overheat, and higher gearing isn’t possible due to physical limitations, best of luck with it, maybe going to 1:3 will solve that
