New motors and electronics FABLE V0.5


#1

Hi everyone, here some ideas about the new fable electronics.
First at all, after a lot of test , i think that servo motors aren’t a good solution because are too fragile, with low power and too much noise and vibration.

The idea is to change servo motors and to use micro motor gear box like this:



Some technical features:

"This gearmotor is a miniature high-power brushed DC motor with long-life carbon brushes and a 297.92:1 metal gearbox. It has a cross section of 10 × 12 mm, and the D-shaped gearbox output shaft is 9 mm long and 3 mm in diameter. This version also has a 4.5 × 1 mm extended motor shaft.

Key specs at 6 V: 100 RPM and 120 mA with no load, 70 oz-in (5 kg-cm) and 1.6 A at stall."

For understand how many full spin did the motor could be used this magnetic encoder:





Some technical features:

“This kit includes two dual-channel Hall Effect sensor boards and two 6-pole magnetic discs that can be used to add quadrature encoding to two micro metal gearmotors with extended back shafts (motors are not included with this kit). The encoder board senses the rotation of the magnetic disc and provides a resolution of 12 counts per revolution of the motor shaft when counting both edges of both channels. To compute the counts per revolution of the gearbox output shaft, multiply the gear ratio by 12.”

In this case electronic is more complex, in fact there are a lot of data bus to control the motors (pwm channels) and to receive feedback (from current sensors, encoders, etc) and extra circuits like dc motor drivers.
A good option could be this driver: DRV8833 Dual Motor Driver Carrier



Some technical features:

Texas Instruments’ DRV8833 is a dual H-bridge motor driver IC that can be used for bidirectional control of two brushed DC motors at 2.7 V to 10.8 V. It can supply up to about 1.2 A per channel continuously and can tolerate peak currents up to 2 A per channel for a few seconds, making it an ideal driver for small motors that run on relatively low voltages.

- Dual-H-bridge motor driver: can drive two DC motors or one bipolar stepper motor
- Operating voltage: 2.7‌‌ V to 10.8 V
- Output current: 1.2 A continuous (2 A peak) per motor
- Motor outputs can be paralleled to deliver 2.4 A continuous (4 A peak) to a single motor
- Inputs are 3V- and 5V-compatible
- Under-voltage lockout and protection against over-current and over-temperature
- Reverse-voltage protection circuit
- Current limiting can be enabled by adding sense resistors (not included)

In this new version, there are 6 dc motors and 3 dv8833 boards.
My idea is to split into two independent MCU, the motors control and the acquisition of emg signals with an architecture MASTER/SLAVE like in figure:

The MCU MASTER acquires and processes the EMG signals and drives the MCU SLAVE which controls the motors, in this way there are enough GPIOs for all and reduce the computational load on two independent MCU.

What do you think about it? any suggestion are welcome


Hi Everyone! I am Carmine
About electromechanical hand
#2

@Oro @Max @Luca_Rizzi @javaonekenobi @Marco_Bugliesi @Gianfranco_Damato and the other guys, what do you think?


#3

Looks great, I like the idea of using the DC motors instead of servo, I’m starting to actually hate the servos :slight_smile:


#4

i love the DC with encoders :slight_smile:


#5

Great improvement for the movement of the new fable and should be also more precise using the encoder


#6

In addition using a splitter architecture should be more flexible in case you want to use a different source of stimulus in place of emg keeping the motor driver in a second line that basically should not change


#8

exactly so @Oro, we could put an emg system or a capacitive system or a couple of switches or whatever!


#9

@Renato did you see the motors? what do you think about the size?


#10

@Renato here the 3d model of the motors

here the .3dm file:
https://github.com/openbiomedical/OBM-FABLE/blob/master/3D%20Model/Fable%20v0.5/motorgear.3dm