Today I accomplished two main things. The first was quite simple. I was able to get the gate driver IC's mounted to the SOIC-8 to DIP-8 breakout boards from sparkfun. The second was to determine where to place the hall effect sensors to meet the needs of the controller as well as find a convenient place to place them physically.
1. Gate Driver SOIC to DIP
SOIC-8 to DIP-8 breakout board
Top view of the Sparkfun breakout board.
The FAN7842 IC placed on the board.
Just making sure it fit.
First completed Gate driver breakout
This was the first gate driver breakout board. Quite simple.
Here is all three completed.
Placed them on a bread board for easy storage for now. After completing these the glue was still not quite cured on the motors. I decided to come back to it tomorrow.
2. Hall Effect Sensor Placement
Now on to the more tricky part of figuring out where to place the hall effect sensors for the motor controller. Controllers usually go with a 60 degree or 120 degree separation between sensors. However the key is that these are electrical degrees and do not correspond directly to mechanical degrees. Fortunately there are a few simple equations that relate the two together and make it easy to figure out where to place the sensors for your particular motor. I read an article written by Jed Storey on his blog that made everything very simple. That blog is found here. I used those equations below to help my hall effect sensor placement. Additionally with this motor there were only a few spots where placement of the sensor would be easy which added an additional challenge.
Side view of Motor
You can see the wide slots on each side of the stator. These are convenient for sliding a hall effect sensor and wires through. These will play a large part in determining the location of the hall effect sensors. The sensors will go up through there and right up against the bottom of the windings. The sensors are too big and the windings too close together for the sensors to fit in the stator spacings. I am hoping (and will find out if it works) that the small gap underneath the windings before the chassis gives the sensors enough room to pick up the bottom end of the rotor magnets.
Basic 9 spacing stator for a BLDC motor
This is a generic diagram for a 9 spacing stator in a BLDC motor. This will be used to illustrate the hall effect sensor placement. The phase winding labels (AaABbBCcC) are just guesses for now. I do not actually know the winding of the motor, I will figure that out later during testing.
Equations application from Jed Storey's blog post
The equations and writeup that I used can be found HERE. It's and excellent brief post that does a great job summarizing everything that he learned on the subject.
Physical placement of sensors dilemma
I needed to igure out a way to keep within the boundaries of the equations as well as get the sensors on the four possible outside slots.
Hall effect sensor placement math / reasoning
This diagram shows how this placement still works with the equations and the requirement of 120 electrical degree separation between each sensor. Even though I could have the sensors one stator spacing apart, these locations were chosen for easy mounting in this small motor.
Which glue do I choose?
I was concerned by the premise of using hot glue on a motor. I know my motor shouldn't be getting hot enough to melt hot glue because if it is I have a serious problem. However I laid out a few samples of each of these glue to see which one I like best. Gorilla gel glue, Hot glue, Silicon caulk glue, Goop all purpose utility glue. The Goop glue was the winner because it had more settling time than the gorilla glue and no where near as long as the silicon caulk. It seemed strong and I felt more comfortable with it than the hot glue.
After Initial Placement
This is immediately after placing the sensors for the first time. Still moveable needed to wait for them to cure.
After Initial Placement (other side)
Other side of the motor after the initial placement.
After curing. Bottom view.
You can see why I chose to place the sensors where I did. Anywhere else wouldn't be too feasible.
After curing. Side view 1
After curing. Bottom view 2
After curing. Top down view
After curing. Side view 2
You can see that I used the metal base as the main support for the hall effects.
I did a continuity test to the metal chassis base between each lead to ensure that there was a glue insulation layer between it and the metal base. I also made sure there were no shorts between each lead.
Resource: MIT pdf on BLDC motor physics basics.