Motor
Motor
In Jordi's original YouTube video, he stated that the motor is 15 cm (6 inches) in diameter and weighs only 4 kg (9 pounds). It makes 15 hp (11 kW) at 10,000 rpm. Impressive!
It looks like a QSMotor design, but I could be wrong. It uses a novel position encoder.
A parts diagram shows the motor having a pinion gear with 25 teeth.
The motor uses ceramic bearings which require a break-in period, during which time more acoustic noise will be noticeable.
Motor Position Encoder
The Dragonfly's motor encoder is a simple device compared to the one EM chose to use. EM's encoder is expensive ($440) and unusual, producing one sine wave and one cosine wave per revolution. Furthermore, the chip inside is likely the sole-sourced AM4096, manufactured by RLS in Slovenia.
Although the Dragonfly's encoder does connect to the SiliXcon's sine and cosine inputs, its waveforms are much simpler - essentially being a crude digital approximation of a sine wave. But this is not inherently bad. Although a high-resolution encoder would be needed to accurately position, say, a robotic arm, it's probably overkill for a trials bike.
Presumably, this simplification still provides sufficient position information while being much cheaper to manufacture. I'm guessing it should retail for less than $100 and is built from widely available electronic components. For example, the more sophisticated magnetic encoder for a Talaria Sting (a small China-built electric motorcycle) retails for about $60.
Likely locations for magnetic sensors circled in yellow
Close-up of motor position encoder and ring magnet
Credit: Phoenixamerica.com
Radial Multipole Magnet Ring
A multipole radially magnetized ring magnet is attached to the motor shaft.
The adjacent photograph shows an example of how the poles would per arranged.
I am guessing there may be 6 poles, alternating north-south (N-S-N-S-N-S) around the perimeter of the Dragonfly's encoder magnet.
Dragonfly Motor Encoder Waveforms
The waveforms below were provided to me by a Dragonfly owner. Some aspects of the encoder's operation remain a mystery. I'd need the encoder in my lab to fully understand it. Rather than an analysis of its operation, I'll just present the following observations.
Trace 1 is the sine input to the controller. Trace 3 is the cosine input to the controller. Both are referenced to controller common.
The SiliXcon controller supplies +5VDC to power the encoder. The encoder's outputs are expected to swing from 0 to 3.3V (but the controller's inputs are 5-volt tolerant). Thus, each waveform's zero-crossing should be biased up at about 1.65 volts to create a virtual ground.
Each full cycle of a waveform spends:
1/6 of its period at zero
1/3 of its period above zero
1/6 of its period again at zero
1/3 of its period below zero
The two waveforms are 1/6 of a period shifted in phase.
Motor encoder waveforms
Motor encoder waveforms, detail view
Motor Temperature Sensor
SiliXcon recommends using the KTY81 series of thermistors with their controllers. Based on a resistance measurement of 1800 ohms at 55° F (12° C) I'm guessing the thermistor may be a KTY81/210 (tighter tolerance) or a KTY81/220 (looser tolerance). It has a positive temperature coefficient. This is an obsolete part according to NXP Semiconductors.
Close-up of motor temperature sensor
Backside of encoder with attached thermistor.
Thermistor Table
Based on very little actual information, I constructed the adjacent table. It is nothing more than an educated guess. The KYT81/220's data sheet lists resistance values at specific reference points 10 degrees C apart. Resistance of thermistors is also typically specified at 25° C. In this case, it's 2000 ohms.
Temperature is converted to degrees Fahrenheit for Americans.
The SiliXcon manual reveals the internal circuit for reading a thermistor is a voltage divider comprised of the thermistor on the bottom with an upper resistor of 10k ohms pulled up to 5 volts.
This allowed me to calculate the voltage divider's fraction and the corresponding voltage measured by the controller.