Views
« Back to the SERA Actuator home page
Contents |
Design Parameters
During the electrical design process, the team sought to investigate all of its options with regards to power, connections, and communication. In addition to meeting performance requirements, the following parameters were stressed while designing specifications and weighing options:
- Widespread and low-cost availability of parts
- User familiarity and ease of use
- Ubiquity of interfacing components
Legacy Hardware Support
While sporting an advanced control mechanism was important to the team to get the most from the actuator, adoption by existing hobbyists was also identified as an important practice to support. Therefore, the team decided to also support the 50 Hz Hobby-PWM standard for position servo control, as well as extending it via a jumper pin to also support force servo control. While many of the feedback information from the actuator would not be available in these modes, their inclusion would allow the actuator to be adopted by a much wider range of users.
Actuator Power
The team consered several criteria when designing the actuator power system. Among these are:
- Motor electrical requirements
- Minimal wiring
- Use of small, flexible wiring
- Connection simplicity
- Availability of batteries
Based on these criteria, a 14.4 Volt power bus was selected. The team discussed including an optional 5 Volt logic power bus, but ultimately decided the added wiring would not be worth the possibility of a soft Emergency-stop system.
As it fits with our Biped Spec, this would allow for 20 Ah of current capacity using approximately 2 kg of weight.
Communications Protocol
» For more, see Communications Spec.
The team explored many options for a communications interface and protocol, including USB, Ethernet, Firewire, Serial, Wifi, and ther wired and wireless protocols. Due to its ubiquity, electric isolatuion, and ability to address several actuators within bandwith constraints, the Ethernet interface and protocol were selected.
Circuit Design
The initial design of the actuator's control circuitry consists of:
- A microcrontroller
- An ethernet controller with magnetics
- An H-Bridge driver
See the image at right for an overview of the circuitry.
Physical Layout
While the physical layout of the board was still to be determined, the picture at left presents one possibility for positions of jumpers, the PWM interface, and two RJ-45 ports.