I’m also refining my motor controller bench test setup. The idea is to have one large motor connected to a test motor via a belt/pulley. The large motor and it’s controller would be there to oppose the other motor and controller that is being tested. I would simply control the braking strength of the large motor to vary the amount of load it is causing on the other motor/controller. This way I can run a whole bunch of controlled conditions and stress tests to benchmark the controller under test.
By active breaking you mean a physical break?
Only way to break a BLDC motor is to phase shift all phases 120 degrees (or was it 90?), which in turn gives the regen current. Or did I miss something?
Motor A would be operating in either quadrant I or III where speed is in the same direction as moment. Motor B (the braking motor) would be operating in one of the other 2 quadrants where speed is opposite of moment. The VESC can actively brake like in quadrants II or IV, no? Of course this is to achieve a braking force greater than regen braking should it be necessary.
Not quite following, I realise the breaking of generative breaking is relative to the speed already on the motor. But you’re talking about force beyond that? essenstially trying to drive the motor the opposite direction to apply more braking force?
Try the current mode on the VESC to get a feel for it, and set the negative ERPM for a low value, once bellow certain speed it enters the active braking, does wonder for direct drive and hub motor, but can also work with geared setups and allows you to break and stay stopped in downhill
Already have that solution active on my madhubs And yes it does wonders on low speeds.The feature is already properly implemented in vesctool by now however
Interesting. I had thought the VESC was only capable of regen braking. Braking beyond that would presumably require direct dissipation of energy. I would guess that would require a big-ass resistor and heat-sink. No?
No. The motor is simply trying to spin opposite of what it is being forced to do otherwise. Like pedaling backwards on a simple bicycle in order to stop.
Will there be some heat dissipated? Yes but only what you would expect from the motor based on the amount of current flowing through it at the time. No resistor necessary. Maybe some forced airflow from a fan on the whole thing to help keep it comfortable.
Yes. It would be actively braking and therefore require energy. This whole setup would be powered by lead acid batteries that are in turn being constantly charged from the AC mains. Power aplenty!
I’m struggling to understand how it’s possible to use energy from the battery to perform braking. Consider a closed system of a skateboard at the top of a hill with a battery, and then let that skateboard roll down the hill. With no external input, the skateboard would pick up speed such that the potential energy (given by mgh) from the top of the hill would become kinetic energy when it reaches the bottom of the hill (given by 1/2*mv^2).
If I didn’t want the skateboard to pick up speed as it descends the hill I could instead convert that mgh energy to electricity and put it in the battery. So again the total energy at the start equals the total energy at the end. The potential energy from gravity is now in the battery.
But if I’m taking energy out of the battery to oppose the motion of the skateboard descending the hill, I now start with mgh from the skateboard on top of the hill as well as a full battery. When the skateboard reaches the bottom, I’ve lost my mgh energy, lost some of the battery energy, and have picked up no kinetic energy from increased speed. The only place for all that energy to have gone would potentially be heat - right?
So unless I’m wrong (which is definitely possible), you can only brake by either charging the battery or by dissipating the energy as heat.
Imagine that when acceleration is request, you are producing a magnetic field that is forward of the current motor position, this produces positive torque, the active braking you are just positioning the magnetic field behind, and producing negative torque
A motor produces torque, it doesn’t care if it’s spinning or not or in which direction it’s going, the controller just need to know the position to create a magnetic field in the position that would produce the desired effect
I don’t think he’s talking about making the motors run in the opposite direction. His diagrams actually show the torque opposing the motor direction. I’m still stuck on the energy question. If the system is gaining energy from both gravity and from the battery - where does that energy go?
Incidentally you quoted me - sort of. But you edited my statement to say something I definitely didn’t say, didn’t mean, and is definitely wrong. I’d appreciate it if you quote me accurately and then respond to the quote.
This is what I’m saying. I don’t think you can slow a motor down by adding energy. I think you have to allow the motor to output energy which can be used to do work, charge a battery, or be dissipated as heat.
but only if that will actually be necessary to achieve the loaded conditions I have i mind.
And yes it does wonders on low speeds.The feature is already properly implemented in vesctool by now however