Project HoverArm


#42

Decide your project, choose drive second :p. I assumed you were planning on an arm like in this project.

A lot depends on your project. 24V would work better for any case that you’re spinning it mostly at slower speeds (if 50% throttle at 48V is worse for motor efficiency than 100% at 24V if there is any ripple in the current)


#43

Hello all.
Just a warning. The magnetic encoder rig are very brittle. To not drop them or press to hard on them.
Broke already one when I dropped it.


#44

@G_Penzo
please send pictures/video about you do the mounting & alignment of that magnetic ring with its encoder because it’s pretty obscure to me.


#45

Can I use an inductive sensor or something similar with the AS5311 and magnet ring as an external index signal? Or does the index signal need to be exact on a incremental pulse?


#46

In principle you can use an inductive “home switch” in parallel with the encoder index, to form sort of a 2-stage indexing. We don’t have code for this yet though.
That said, if you don’t require the full repeatability of 16-bit, you could probably just use the external sensor as an index.


#47

I ran a hoverboard motor from 2x6s lipo in series for just a smidge over 50v and got a top speed of 16mph, average 13mph on some slight gradients. Stall conditions under braking while powered were 15A, about 740 watts.


#48

That was what I was thinking. The AS5311 gives an index pulse for every pole pair, so we can’t use it for now. So if I only use the incremental part of the AS5311 and a separate index pulse from a inductive/hall sensor, it will only need to find the index on each startup after first calibration? I want as little movement on each startup as possible, and the motor position will not be maintained when it’s off!


#49

Would it be possible to use one of the built in hall sensors in the hoverboard motors as index for the encoder? It’s a 27 stator pole motor. What if I treat it as a 3 pole motor, and use the rising edge of one hall sensor as index. And devide the pulses from the AS5311 by 9. I might not get perfect position control this way. But all I want is to run the motor as slowly as possible, and with as little start-up movement as possible.


#50

Correct.

Hm this gets messy because the rising edge of that signal is at a different place depending on which direction you come from. Maybe you can work around this by rotating one way, and only “arm” sensitivity to the index edge after half an electrical turn or something. This means you should get a consistent side of the pulse’s width.


#51

I’m just trying to look for a solution, without being an expert.
I’m still thinking that this might be a solution.

The magnetic ring and the AS5311 fits inside the motor with just two 3D printed brackets. See photo. No modifications to the motor needed. At least as long as you don’t need cooling.
Also AMS claims that the AS5311/ring combo is immune to external magnetic stray fields. (I guess that means it will not be affected from the stator poles being close?)

Vdd and Vss can be taken from the hall sensor PCB. and wires from two hall sensor can be used to connect to the incremental pins on AS5311. The last wire remain on a hall sensor. No extra wires needed.

Use rising edge on hall sensor when the motor is spinning in one direction and falling when it’s spinning in the other direction.

The number of pulses from the AS5311 between each hall sensor edge is known.
Even though the number of pulses between each index is not a hole number, and each pole is not a perfectly equal magnetically, it should not matter for a EV built.
9709.037 pulses between each of the 27 poles from my calculation.


#52

As far as I understand, the hoverboard motors usually have 30 poles and 27 coils.


#53

When I write stator poles, I mean coils. I see I forgot to add stator one time.

I was hoping this forum could help me finding a solution to finish my project. When I started I thought it would be easy to find a driver for the hoverboard motor. But since my nephew is very young, I need it to drive very slowly, and that seems to be a problem. I have no space for an external encoder. Also, I can’t have the motor rotating too much at startup.

If you don’t think I’ll be able to use odrive, I’ll start looking for another solution.
Maybe ditch hoverboard motors and instead use geared motors.


#54

I think we will make hall effect encoder input available within 1 month, so then you should be able to use ODrive directly.


#55

Excelente… I’m looking forward. Thanks.


#56

Did any one of you had success using the as5311.
After trying 2 chips from ams and two chips from mouser. I still cannot get the chip to work.

When stationary and looking at the pwm signal it looks good.
When moving the motor a bit by hand I see the pwm duty changing. So the chip works.

While looking at pin A and B I get allot of garbage.
Based on documentation they implemented Incremental Output Hysteresis.
But what I’m seeing on my scope looks like the sensor thinks the motor is moving, vibrating. The motor is not connected to the odrive it is stationary.
So anyone succeed with this sensor.

I’m thinking to drop this sensor and use a traditional encoder connected with a timming belt.

Regards Grayson.


#57

Once I got it working it was working very well for me. I used this breakout board from mouser. There are two things that I didn’t find obvious that I can share.


You must pull nCS to gnd to activate the incremental (A,B,Z) output. This is what I’m doing with the purple wire here.


The sensor center is not in the center of the package, is slightly off to one side. You can see this in the datasheet, and the dotted line on the breakout board.