Table of Contents
With MSD I coming to an end, loose ends are to be tied up and the final design decisions will be made with the customer during the final Gate Review. The updated customer requirements as well as engineering requirements are posted and the electrical and mechanical subsystem designs were updated for any changes. The plans for the next phase during MSD II are outlined below.
MSD II PlanningThe P16051 team came together and made a plan for the MSD II Phase. See image below:
Mechanical SubsystemsThe team developed two different concepts for improving the Teknic Clearpath motor's resolution and accuracy.
One concept on the mechanical side was to use an N-bar linkage assembly. The motor would be able to either rotate continuously, or back and forth in a 180-degree range, while the output would be the same for either. The motor would drive the red link on the left, while the green link on the right would act as the moment arm, rotating the model eye assembly about the fixed point.
The second concept would utilize a piston-cylinder assembly, shown below. This sort of system (or use of a slider on a track, or a sliding collar on a shaft) would translate the motor's rotational motion to linear motion, while the piston can push and pull the moment arm, resulting in eye rotation. The advantage to this system is that the piston's motion will be linear, meaning the mathematics of the system would be somewhat simpler to model.
Electrical SubsystemsThe Teknic ClearPath CPM-MCPV-2311S-ELN motor is an all-inclusive motor which combines the motor, encoder, and motor controller into the same package. The motor receives power from a 4-pin Molex connector which connects to a power supply also sold by Teknic for the ClearPath series of motors. The motor interfaces with any personal computer via a USB and also receives inputs as well as provides output with the 8-pin Molex connector.
In doing preliminary testing for the motor, connection to a PC running the provided MSP software will be used. The motor will connect via a USB Micro-B port on the back of the motor to a USB A port on any computer.
The initial testing involves operating the motor via the MSP software in order to learn general functionality. This will be brief, as the motor will primarily interface via the Teensy microcontroller and not a PC.
The pulse burst positioning mode allows the motor to move to any position, as it is based off of the amount of pulses sent to its input. The microcontroller will send pulses via PWM outputs and further testing will be performed in order to deduce the exact proportion of pulses to angle movement.
On the motor's 8-pin Molex connector, there are a total of 4 I/O ports; 3 inputs and 1 output. The Enable input is an active high and tells the motor when to receive and acknowledge inputs. Inputs A/B allow pulses to be sent to the motor to control behaviors such as velocity and position depending on the mode the motor is running in. The High Level Feedback output allows data to be sent from the motor to a device in the form of pulses. This data can consist of velocity or even a position indicator when the motor has reached within 10 counts of its destination.
In order to power the input pins, a minimum voltage and current rating have to be met. The motor requires a minimum input voltage of 5V at 8mA. The Teensy 3.1 microcontroller can only provide 3.3V of PWM at 9mA which is under the requirements. In order to rectify this, a 74HCT245 voltage buffer would be needed to level shift the 3.3V to 5V, however this adds more complexity and cost to the design as a circuit board would then be needed in addition to the microcontroller. A simpler solution is to switch microcontrollers and go with an Arduino Uno. The reasoning for this is that the Uno can provide 5V at 20mA for digital output. The programming will be the same as the Teensy would use TeensyDuino whereas the Uno would use regular Arduino. In speaking with the engineer at Teknic, they recommended using an Arduino for any interfacing with motors.
The power supply to be used in powering the motor is the Teknic E3PS12-75 1-channel power supply which would be able to provide the ClearPath motor in any scenario. Cables for this are available such as:
- 10-pin Molex Wall-to-PSU (E3PS12-CABLE110)
- 4-pin Molex PSU-to-Motor (CPM-CABLE-PWR-MS120)
- 8-pin Molex Motor-to-Leads (CPM-CABLE-CTRL-MU120)
Bill of Materials
Our Bill of Materials has slightly changed from the last review, please see below:
Updated Customer and Engineering RequirementsThe only change from the initial start of the project to the Gate Review was the addition of crossplatform support, specifically with Mac OS X. This change was incorporated into both the customer and engineering requirements.
Additionally new risks have been identified for this phase, as outlined below.
At the end of this phase our team met and talked about MSD I as a whole, we then filled out the team self critique found below.
Gate Review Materials
Gate Review Presentation here
- Email Jeff to confirm when we will be presenting the tradeoff space to him in person over break - Amy
- Start the trade-off space presentation - Amy
** Within the presentation each person will be responsible for a slide representing the work that they did on all action items assigned to them - Team
- Meet with Topic Specialists to determine optimal system design - Josh
- Get measurements from the Alpha Team - Amy
- Order motor and Ardiuno - Nate
- Model 'Eye mounted directly to eye shaft' in SW - Jordan
- Model 'Eye with 3-bar linkage/moment arms' in SW - Amy
- Update both BOM with information from the SW drawing - Nate
- Make GUI to perform math for 3-bar linkage - Peter
- Look at Alpha Team's finished code and determine what we can use/start any coding we possibly can - Peter
- Look into make a jig - the Teknic motor with a short arm to use with alpha teams design - Nate
- Meet with Abe this weekend by phone - Team
- Meet with Jeff over break and present above work (additionally try to make time before the meeting with Jeff to do a quick run through via Skype) - Team