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Jun 29, 2014, 05:34 PM
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back EMF

It was worth documenting the last bit of data from the back EMF motor control fiasco. It begins with the full power applied.

Oscilloscope plots of the full power voltage are never shown, but they have the clearest view of the 2 powered phases with the back EMF clearly visible in the floating phase. There's a glitch where it goes from 9V to floating. Software detects the halfway point to determine the commutation time.

The normal oscilloscope plot shows PWM modulated voltages. The back EMF phase is less visible. The writers for EETimes tend to be more interested in showing they fully understand the concept personally, with the most obtuse diagrams, rather than conveying it to someone else.

Back EMF fluctuates from PWM on the other 2 phases. It must be sampled on only 1 edge of the PWM, which limits the number of samples to the PWM frequency. PWM didn't work completely. It had to be done in software to get all 6 pins transitioning.

The G-buggy's front wheels were held in by a very robust 1/8" metal bolt, press fitted into plastic. It could have been hammered out, straightened, & hammered back in.

The G-buggy's electronics are repackaged in all the Maesto toys.
The New Bright toys have proportional throttle but not proportional steering. Nothing under $80 has proportional steering. It's a question of how much you're willing to pay to run fast, at a certain age.

The king is the $80 Losi Micro T, with the highest speed of anything its size. They're always upgraded to 12mm motors, 2S 190mAh batteries. There's a guy who spent $150 & 3 months building one from scratch. He said it lasted 20 minutes on 200mAh.

$42 Chassis: ... cing/8837/

$4 Stock a-arm set: ... Losi/9048/

$10 Losi Micro T Light Blue Aluminum Rear Knuckle Hubs: ... cing/9177/

$11 Losi Micro T Light Blue Front Knuckle with Threaded Shafts ... cing/9179/

$11 Losi Micro T Steel Universal Swing Shaft CVDs ... cing/9178/
$1.37 HK-250GT Ball Bearing 5 x 2.5 x 2mm (4pcs/set)

You will need 2 sets: ... duct=10252

$7 Losi Micro T Blue Aluminum Rear Arm Mount : ... /GPM/9406/

$5 Losi Micro T light blue Front suspension mount ... cing/9181/

$16 Losi Micro T light blue gear box gearbox ... cing/9176/

$14 Team Losi Micro T Complete Assembled Transmission : ... Losi/8676/

$4 Losi Micro T, Baja Wide Front Bumper: ... /RPM/9489/

$5 Losi Micro T Suspension Mount & Bumper Set: ... Losi/9047/

$7 Team Losi Micro T Clips, Wheel Shafts Suspension Set : ... Losi/8467/

$4 Team Losi Micro T Screw & Pin Set ... Losi/8681/

$9 wheels ... Losi/9799/
Last edited by Jack Crossfire; Jun 30, 2014 at 02:00 AM.
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