My friend and I are building a tracked rover for a mars-like challenge in the sand on April 2nd 2011. http://spacegrant.colorado.edu/index.php/robotics-challenge
I know now we should have done some research/calculations before purchasing parts. But now we are to the point of make it work or start over.
We purchased 3 lengths of the 2 inch track using one and a half lengths for each half of a 2 tracked tank
We also purchased hubs, idlers and 2 GHM-13 6mmshaft 12vdc 50:1 152rpm motors.
We are using 2 L293B h-bridges in parallel(for higher current) for bidirectional motor control.
For a power source we are using a 16.8vdc Li-po battery(made from cell phone cells).
We are regulating the logic level voltage at 5vdc with an LM294ct with a 100uF cap across GND and Vout. and The reccomended 0.47uF cap across Vin and GND.http://www.national.com/ds/LM/LM2940.pdf
We have soldered three 0.1uF caps on each motor, one from each lead to the motor housing and one between each the leads like they recommend here.http://www.pololu.com/docs/0J15/9
I have also added 0.1uF bypass caps at every Vcc and Vdd to gound right next to the chips.
We have diode protected the hbridges like they recommended on the top of page 2 of this datasheet.http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1328.pdf
We are using microchip pic16f886 microcontroller to provide the pulse width modulation and direction signals.
We have run into a few problems.
1. I think the motors are not strong enough to drive our platform at a low speed(50% pwm ~8.4 volts). We only need 1 - 2 mph, not the 3-5 mph we get at the full 16.8 volts.
2. When the track segments slap around the bottom sprockets while moving at a normal speed (70% PWM of 16.8 volts ~ 11.76v) on a flat ground or rocks we are still getting some transient spikes back into the breadboard where the microcontroler is causing false trips of our bumper limit switches. This does not happen if we run the motors while holding the tank off the ground.
3. This back EMF is a huge problem considering we will be communicating via I2C and SPI a radio transceiver and a 3axis compass/accelerometer combo among other sensors.http://www.parallax.com/tabid/768/ProductID/582/Default.aspxhttp://www.pololu.com/catalog/product/1250
Question: Should I eat the cost and get some higher geared motors, or is there a way to make our current setup work?
Also I have heard there might be a way to change current instead of voltage(PWM), does anyone know if/how that would work?
I can get a youtube video up of the demonstration of my problem sometime tomorrow if that would help.
Thanks a bunch!