billvon wrote: ↑
Jan 24 2019 1:08pm
DanGT86 wrote: ↑
Jan 23 2019 8:48pm
This last pic is the hall signal from the 9c hub motor for comparison. It also seems to go under 4v in the on state but still looks cleaner and less noisy to my untrained eye (I borrowed the scope and have about 1 min of training on it)
1) That could be your scope probe picking up some of that through coupling to the power signal. So it may not be all real.
2) That could also be the phase (power) line coupling to the Hall sensor lead which is real. A stronger pullup will help there. Also, an RC filter might help on the signal itself. For example, a 100 ohm in series, and a .01uF from controller pin to ground (at the controller end not the motor end) would give you a filter at 150KHz which should help.
3) It might be noise on the 5V line but probably not. A 1uF or so ceramic (NOT electrolytic) cap between +5 and gnd at the Hall sensor may help there.
Be careful with a "stronger" pull-up resistor. 41F halls (or just about any hall used in BLDC motors) are current sink devices. They have to overcome the "pull up" current from the resistor to "pull down" to 0v and they can only sink 20mA. This is a very small amount of current and easily overcome with a "stronger" pull-up resistor.
Where are your halls located? If they are on top of the motor and then the hall wires have to pass through the stator to exit the motor, this will induce the most noise on the halls. Halls placed as close to the exit of the motor as possible is the best.
Are your halls placed where they directly face the magnets? It's fairly common that the halls are offset from the magnets so they don't directly "read" the faces of the magnets as they pass by.
How close are your halls to the faces of the stator teeth? You want the hall faces flush with the surface of the stator teeth. If they are inset some, this will diminish their ability to detect the magnets.
The hall at the bottom of the stator is very close to the exit of this motor, It is also placed flush with the face of the stators. It's in the stator so that magnets can pass directly in front of it. IE: It will get the best possible "signal" from the magnet with the least amount of interference. The hall on the board is above the stator so it doesn't actually face a magnet directly. It's inset from the stator faces by about 1/4". It's wires have to pass down through the stators to exit the motor. This is far less optimal. It works, but it's not as "clean".
This is optimal hall placement. The hall cable immediately exits the motor. The halls are directly exposed to the faces of the magnets and they are flush with the faces of the stator teeth.
This is pretty good with the exception that the halls are not directly facing the magnets, but it's as close to the magnet faces as I could get. It does meet the other 2 goals: At the face of the stator teeth and the cable exits in the shortest path.