My robot is "looking for love in all the wrong places" (occasionally).
I need to find an electrical engineer to love him for some very brief moments.
( *Spikes* his hair just thinking about it. )
Some of the design parameters of my 16 year old Rug Warrior Pro robot, (that I am doing a brain transplant on), were:
- small size (8" dia. 5" high)
- 7.2v 5000mAh (6 * 1.2v) C-Cell power
- full skirt for bump detection and protection
(The robot was an MIT robotics lab design at the time - over 300 non-MIT people built this little guy.)
I have replaced the prior single robot board HC6811 processor, interface hardware, and sensors with:
- Raspberry Pi (B+ at the moment, soon with the element14 Road Test sponsored Pi 3B)
- Mikronauts Pi Droid Alpha interface kit board (16 digital I/O, 8 ADC, 8 Servo, Dual H-Bridge Motor driver)
- Pi Camera, HC-SR04 Ultrasonic ranger, ACS712 5A current sensor,
- Pololu 5v 2A step-up/step-down switching voltage regulator (model S18V20F5)
The Mikronauts Pi Droid Alpha card is really feature filled and well thought out. (It is a simple kit for accomplished builders.)
Power Bus:
- Raspberry Pi is running on the regulated 5v naturally: 4.75-5.25v spec.
- Motors use unregulated full supply direct from the batteries: 3-8v spec .
- Servos are running on the unregulated 4-cell tap: 3-7.2v spec. - (4-cell tap supplies 3.6 to 6v unregulated)
- HC-SR04 is running powered from the regulated 5v supply (that the Pi uses): "5v" spec
Normal running parameters:
- Idle: 270mA total draw (servos quiescent, HC-SR04 and camera off, motors stopped, python time.sleep(10) running, no ssh activity over WiFi )
- HC-SR04: +10-30mA average
- SG90 Servos: (one at a time) +80-330ma with 730-1450ma spikes, (230ma average)
- Drive Motors: +230-1200mA (330ma average at maximum fwd/bkwd drive levels)
Note: The unregulated 4 cell tap reaches 5.9v when batteries are fully charged (at the end of charging the 6-cell bank)
I do not have a scope to help identify if this is noise, back EMF, current draw spikes. Not sure what else could be going on either.
Issues:
- The HC-SR04 operation causes occasional reboots
Constraints:
- The HC-SR04 needs regulated 5v so I cannot run it from the servo supply.
- Single power bank (single recharge connection, single pole electronic on/off switch)
Suggested Remedies:
- 5v regulated power conditioning (caps? coil?) to the Raspberry Pi?
- Surge capacitor on HC-SR04 5v?
- HF shunt capacitor on the HC-SR04 5v?
- ??
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