Have somebody seen my magic smoke?

A little while since the last post, this is maybe old information if you have read my posts on Endless Sphere or the Swedish Electronics Forum. We played around for the whole weekend with the moped until the motor got enough. My guess is that several hard accelerations during a short period of time heated the stator enough for the insulation to melt.

The black insides of a BLDC motor
The black insides of a BLDC motor

Not pretty! I’m afraid I’ll have to torment my hands with another rewind. A member on SEF is good enough to donate a large roll of 1,5 x 2,5 mm flat copper wire to me which I will use for the rewind. I have three different actions to prevent this from happening again.

  • Increase the gear ratio. Less torque on the motor means less current.
  • Increase kv, one less turn of copper wire will increase kv to match the higher gear ration and reduce the resistance. It will also leave more room for air to flow through the motor
  • Forced cooling, I’ll put a fan in one end of the motor to force more air through.

I’ve also ordered a spare motor from china. The 80-100 is very hard to get nowdays, but I found a 80-85 motor with the same mounting profile and axle. But i’ll keep a close watch on the stock of the 80-100 motor.

First testrun of the E-Puch

Today I’ve made the first test-run of the E-Puch. As I’ve written about before it is an old ICE moped that I’ve removed the engine and replaced with an electric BLDC outrunner.

Today, me and my brother threw everything together for a quick testrun just to see that everything works, and try out the performance.

E-Puch ready for testrun
E-Puch ready for testrun

I will soon write a post about the motor controller which I ordered from a guy named Lyen on the Endless Sphere forum. It is currently set to limit battery current around 40 A, but I think I could increase the current limit by 50% without any modifications. Which would give 50% more torque.

Controller temporarily mounted to the frame
Controller temporarily mounted to the frame

The motor is mounted on two 5 mm aluminum sheets that are bolted in the original motor holes in the frame.

Motor and motor mount
Motor and motor mount, I think I'll remove the axle on this side.

Except for the motor and motor sprocket the drivetrain is original.

Original chain with 10 tooth front sprocket and 43 tooth rear sprocket
Original chain with 10 tooth front sprocket and 43 tooth rear sprocket

I use 4 bricks of 6S 5 Ah Turnigy 20C batteries mounted in 12S2P configuration. For now these are in a plastic box on the rear end of the moped.

Temporary battery box
Temporary battery box

And at last a video of my father trying the moped.

Modifying the Turnigy 80-100 Brushless Outrunner – Part 3

Continuing on: Modifying the Turnigy 80-100 Brushless Outrunner – Part 2

As I’ve written before I had problems getting the Turnigy motor to run in sensored mode using the modified cheap-o eBay controller. Just to se if It’s the controller that is the problem I’ve tried the motor with my e-bike controller.

SUCCESS!

It works perfect! Turns slow and have lots of starting torque. I didn’t try more than 15%-20% throttle and the battery was empty in my current meter so I could’t measure the current. I will try full throttle and measure the current as soon as I’ve got a new battery.

The motor looks much neater with the internal sensors than the external I think I’ll paint it black to match the black moped when I’ve epoxied the stator and not going to take it apart again.

Turnigy 80-100 with internal sensors
The motor looks much better with the sensors mounted internally

Compared to the externally mounted sensors

Sensors mounted in bracket
Sensors mounted in bracket

Modifying the Turnigy 80-100 Brushless Outrunner – Part 2

Continuing on: Modifying the Turnigy 80-100 Brushless Outrunner – Part 1

This is a picture of the rewound stator. As described un the previous post the stator is now wound for ~90 rpm/V using double 1.5 mm copper wire. To hold the windings in place I use some dabs of low temperature heat glue. This will most certainly melt if I would put 3 kW of power through the motor, but I will replace the heat glue with high-temp epoxy when I know that everything works.

Rewound stator
The stator has been rewound with double strands of 1.5 mm copper . The heat glue is just to hold the windings in place while testing. Before using the motor under heavy load, the heat glue will be replaced by epoxy.

The motor is wound as an Distributed LRK (DLRK) and terminated in Y-mode. Using the notation from the picture below, S1, S2 and S3 are connected to the motor controller and E1, E2 and E3 are soldered together inside the motor.

DLRK
The DLRK winding scheme. I've connected E1, E2 and E3 together and use S1, S2 and S3 as phase wires for a Y-termination. The sensors are mounted between 1 & 2, 5 & 6 and 9 & 10.

In the previous post I used ATS177 sensord mounted in a bracket outside the motor. This didn’t work very well with the modified controller. This itme I will try SS441A hall sensors, which are more expensive but thats the sensor that is usually recommended on the Endless Sphere Forum. I will also try to mount the sensors inside the motor which I hope will  be more robust and better looking. The sensors are mounted between slot 1 & 2, 5 & 6 and 9 & 10. Which gives them 120° spacing. To hold them in place before applying epoxy I use the same low-temp heat glue and a little kapton tape.

Sensor in stator slot
The sensors is mounted between two teeth of the same phase on the motor, all three sensors are 120° apart. To hold them in place I applied a small dab of hot glue and some kapton tape (the brownish tape in the image)

When I tried this setup with the modified controller it still didn’t run in sensored mode which leads me to suspect that there may be something wrong with this controller. I didn’t have time to do any thorough investigations why but my next step will be to inspect the sensor signals on the oscilloscope and try the motor on my other controller which doesn’t run at all without sensors.

Continue to: Modifying the Turnigy 80-100 Brushless Outrunner – Part 3

Modifying the Turnigy 80-100 Brushless Outrunner – Part 1

Modified Turnigy 80-100 on testmount
Modified Turnigy 80-100 on testmount

The Turnigy 80-100 is a electric motor sold by Hobby King to replace gas engines in large RC aircrafts. To use this motor in my application two things have to be modified. Installing hall-sensors and re-winding the motor for lower speed. This motor is a BrushLess Direct Current (BLDC) outrunner. This means a couple of things:

  • The motor does not have brushes like an ordinary DC motor. Instead the commutation (switching the current direction the motor windings) is done electronically with high power semiconductors (most commonly MOSFETs)
  • It runs on DC power which is a little confusing since the motor actually is a 3-phase AC motor. But the motor+controller runs on DC.
  • Outrunner means that the motor shell is rotating while the center is static. The center of the motor contains the windings and stator core while the outer bell with permanent magnets are rotating.

Since the commutation is done electronically the motor controller must know when to switch direction of the current. This is done in one of two ways:

Sensored commutation:
The motor is fitted with 3 hall-sensors which sense changes in the magnetic field of the rotor

Sensorless commutation:
Since only 2 of 3 phases of the motor are energized the motor back-emf can be measured on the third terminal to determine rotor position.

This motor is intended to be used with a sensorless controller and has no hall-sensors. A sensorless controller need to spin the motor up to ~10% of maximum rpm in synchronous mode before the back-emf is large enough to measure. Below this speed the torque isn’t very high which works fine for a propeller drive but not on a moped where full torque is required from 0 rpm.

In general BLDC motors and controllers intended for RC toys are sensorless and use sensorless controllers while motors and controllers for E-bikes are sensored. There are exceptions from this but it’s good to know since a sensored controller will not work with a sensorless motor, the other way around could work but the low-speed performance will probably be bad and there is a risk of damaging the motor and/or controller.

To get good starting torque and be able to use an ordinary e-bike controller I mounted hall sensors on my motor. This process is well described in a thread on the Endless Sphere forum:

Adding hall sensors to outrunners

To summarize the +20 pages thread there are two ways of doing this

  • Internal sensors are mounted between the stator teeth at 120° spacing
  • External sensors are mounted on a bracket outside of the bell, this uses the magnetic flux leakage to sense the magnets on the other side of the bell.

Another problem with using the motor in it’s original configuration is the Kv value. This is the constant that determines the motor maximum speed based on the input voltage. For example a Kv value of 1000 rpm/V will result in a maximum speed of 12000 rpm with a 12 V battery. This value depend on several properties on the motor but you can say that it represents the coupling between the current and the magnets. More turns of wire around the stator and/or stronger magnets will reduce the Kv value. The Kv value is also dependent on if the motor is terminated in wye or delta. The same motor have a Kv that is sqrt(3) = ~1,73 times higher if it’s connected in delta than if it is connected in wye.

When I bought this motor it had a Kv of 180 rpm/V and I want it to be ~90 rpm/V. Each stator tooth had 6 turns of copper wire around and the motor where coupled in delta mode. By rewinding the motor with 7 turns on each stator pole and couple the motor in wye instead the resulting Kv is somewhere around

[latex]
180 * \frac{6}{7} * \frac{1}{\sqrt{3}} = 89 rpm/V
[/latex]

This is not an exact calculation since it depends on flux density, magnetic saturation of the stator iron and so forth but it will giva a hint. As i calculated in a previous post, this is enough for ~60 km/h using the same 44.4 V battery as I use on my E-MTB.

There is a thread on Endless Sphere about rewinding this motor as well
Re-wind of a Turnigy 80/100
Rewinding a motor is a tough job but the original winding is done with many parallel thin wires and in a pretty sloppy way. Instead, I used two parallel strands of 1.5 mm copper and it ended up almost as sloppy as before. I seem to have misplaced the photo of the stator with windings before the re-wind but it looked very similar to the pictures in the first post of the thread above. This is how it looked when i were done.

[Will replace with photo next time i disassemble the motor]

When mounting the sensors I choose the method of mounting them externaly. I used a CAD program to draw this mounting bracket.

Drawing of sensor bracket
Drawing of sensor bracket

Mounting the sensors 17,14° apart instead of 120° works because the motor have 14 magnet poles.

[latex]
\frac{120^\circ}{\frac{14}{2}} = 17.14^\circ
[/latex]

A nice guy on a The Swedish electronics forum helped me print two brackets on his 3D-printer and they turned out great!

Plastic sensor brackets printed on 3D Printer
Plastic sensor brackets printed on 3D Printer

With wires mounted on the sensors and the sensors temporarily glued in with heat glue (I’ll use epoxy when i know that it works).

Sensors mounted in bracket
Sensors mounted in bracket

In the pictures above the motor is mounted on a plate that i made to test this way of mounting the sensors. Just to get it running I used a Hobbyking SS Series 190-200A ESC after the rewind this controller had a tough time getting this motor running. Using a 3S LiPo battery it managed to get the motor into closed loop back-emf sensing mod about one time out of ten. With a 6S LiPo it worked perfect and had loads of power! The no-load current consumption was slightly over 1 A, which is great but mostly dependent on that I didn’t re-install the skirt bearing. This motor have been reported to have a no-load current of ~9 A with the skirt bearing and coupled in delta. I also measured the Kv constant to ~89 rpm/V exactly as calculated.

My next post on this project will be about my modified eBay cheapo e-bike controller and hopefully a video of the motor running in sensored mode.

Continue to: Modifying the Turnigy 80-100 Brushless Outrunner – Part 2