Fall 2016 Biped Trade Off Study- Motor
Battery Selection
By: Alan Valles (Electronics and Control Engineer)
Approved by: Ijya Karki (Project Manager)
Table of Contents
Introduction
The walking Biped robot requires a dc motor to control its walking motion. A DC motor can vary in specifications such as operating voltage, current, RPM, torque, and size. Therefore, it is necessary to pick a DC motor that will operate within our electronic system. Furthermore, the customer requested that the walking motion be produced using DC motors.
Study
Most hobby or toy DC motors operate at a high RPM in the hundreds or even thousands of revolutions per minute. Our current mechanical design has us use a Tamiya gear box in order to step the RPM done and to increase the torque ratio. The Tamiya gearboxes are usually recommended for this since they are flexible in the gear ratio available in one single kit. For example, the Tamiya 70167 Single gearbox (4-speed) Kit has 4 possible gear ratio configurations, 12.7:1,38:1,115:1, and 344:1. Thus, to meet schedule requirements an all in one Tamiya motor and gearbox subsystem is preferred. However, The Robot Company has existing components that are GM-9 which will also be considered.
Table 1 Motor Comparison
| Motor | Manufacturer | Voltage | Stall Current | NoLoadCurrent | RPM | Torque | Cost |
| 70167 | Tamiya | 3V | 2100mA@3V | 150mA@3V | 12300 | .5 0z-in | 7.55w/gearbox |
| 1117 | Pololu | 6V | 800mA@6V | 70mA@6V | 11500 | N/A | 1.99 |
| GM9 | SolarBotics | 3-6V | 400mA@3V | 50mA@3V | 40RPM | 44oz-in | Free |
The will output 5V so actually testing will need to be done. As Table 1 shows, the motor that comes default with the Tamiya gearbox will be much higher than the required stall current. The PTC fuse is rated for 750mA so this is our driving constraint. Pololu 1117 is just above the PTC rated value so it should be sufficient, but more testing must be done to verify. In conclusion, it is recommended that the Tamiya Gear box be used, but the default motor be replaced by the pololu 1117 which is the same form factor. Secondly, a design which utilizes a single GM9 will also be considered. It is important to note that the DCDC converter outputs 5V. Thus, the motor will be driven at 5V. It has been shown that running Tamiya motors higher than spec voltage is adequate at 5V to meet mission profile[4]. However, this will shorten the life cycle of the DC motor and is not recommend but it is an option.
Conclusion
In Conclusion, The Pololu 1117 DC motor with Tamiya Gearbox in the 70167 will be utilized in the BiPed Design. The gearbox will allow for flexible configurations resulting in adjustable torque and rpm outputs. Furthermore, the motor chosen will utilize a 130 hobby motor form factor which is required to integrate with the Tamiya gearbox.
Resources
[1]https://www.pololu.com/product/118
[2]https://www.pololu.com/product/1117/specs
[3]https://www.pololu.com/product/188/specs
[4]https://www.pololu.com/docs/0J11/all#3