SCRC:Indoor Robot-Magellan: Power
This page is part of the Project:Indoor Robo-Magellan (SRS Pop Can Challenge) group project. All systems requiring power shall push their specific requirements to the power team. Please include voltage and current requirements even if they're estimations. The battery load will be calculated and tested to ensure the robot has adequate power for the maximum competition time plus a 20% margin.
This is a very preliminary outline"
Anyone wishing to work on this team should reach out to Chas (chas@ snocomakers / com) for coordination and tasking. We will likely have independent coordination meetings in Everett.
On-Board Power Available
Currently planned power supplies include:
- 12VDC at 8A fused at 10A.
- Drive Motors: 5.6A
- 5VDC, 2A
- 3.3VDC, 2A
- 6V, 2A
Power System Overview
As currently envisioned by this team: The microcontroller system will be powered up by a main power switch. The microcontroller will power the 12VDC power relay to all systems which have moving parts. An emergency STOP switch will disconnect power to all moving parts systems.
The document screenshot below is simplified and does not include any current sensing or fuses, etc.
I've purchased this power relay as an option to use as something the micro(s) will turn on the "moving" items power to motion controllers once the micros have fully booted. The relays are NOT /ENABLEd which isn't great but we can work around that with the E-STOP button. Also the relay can be triggered off 3.3V or 5V (tested) despite being sold as 5VDC relays. The current draw on IO is < 3mA. The board is 39mm x 51mm with screw centers on 33mm and 45mm. It appears 4-40 screws would fit the mounting holes.
Schematic... note how the optoisolators are connected for control.
I also purchases an E-STOP (N.C.) button with a momentary "start" switch. The micro which controls drive will have to debounce this start switch.
A 12V 8AH SLA battery will feed core power supplies with an efficiency of greater than 80%. All high current systems will be switched by relay. A standby switch will activate logic power supplies (5V and 3.3V). All motor supplies will be disconnected by relay. A start/stop button will be debounced by the power control board and provide a point to be monitored by the microcontroller (3.3V or 5V?), the microcontroller will when provide an output to enable the drive power relay (3.3V or 5V) the signal will be <10mA and be optically isolated, the stop position will kill all motor voltage regardless of microprocessor commands.
I like this battery and the plan to implement it. The main switch gives power to the "brain". Once it's happy, it outputs a signal to turn the relay on and drives the motors. Kill the main, kill all the power.
I think we will need three switches:
- for the "main" power
- for the motor/kill power.
- start switch
We will need to have the main power startup the computer(s) and be "ready", the start switch will tell the robot to start, and the "kill" switch will interrupt all power to mechanical devices but let the computer run so it can be shutdown properly. This can all be handled by the power supply and give the microcontroller the start/kill signal -- Chas
Power Supply Regulator
I decided to just purchase pre-made power supplies because my v2 board had an error I decided no to hack. They are 2 amp pololu power supplies.
The TI LM2717 was selected as a dual output regulator configured for 3.3V and 5V DC output. The rated output of the regulator will not be taxed; in the first round of design passives with a 1.8A output rated have been selected for a rated power supply output of 1.5A per channel. The [LM2717 Spec Sheet] rates the outputs higher but for relability and heat dissipation there is no reason to push the output of the device.
After changes in power requirements and testing of the first boards we have now moved on to the AP1509 regulator from Diodes Inc. This two amp output 8 pin SOIC regulator will be used for 5V, 3.3V and a 6V output. Fused battery power will also be available. All system leads shall submit their requirements so power can be made available.
Weight & Space Requirements
Max Weight: 25lbs.
Current Sub-system weight is estimated at 5.5 lbs.
- Battery: 5.05 lbs
- Width (in): 2.5600
- Length (in): 5.94
- Height (in): 3.69
- Electronics: < 0.5lbs
- Unknown, configurable; less than 4x4x2"
- Waiting for parts, ETA early June.