DC Motors not responding well to voltage.
w00t_86
Posts: 12
Currently i have a setup where i'm using a Basic Stamp BS2sx to interface with 2 motor drivers that i bought. The motors are rated at max of 12VDC and 2.5A. I'm planning to use a battery which has a nominal rating of 7.2VDC (max 8.4VDC) and 3300mAh.
I used a bench analog voltage and current supply at 8.4VDC and found that the motors did not respond well to the program i wrote. However, when i lowered the applied voltage to around 6.5VDC, the motors ran without problems (albeit slower than what i desired). Similar results occurred when i used the battery that has the nominal rating of 7.2VDC (max 8.4VDC).
I am puzzled and asked a lab technician regarding this problem and he too could not troubleshoot what was the problem. The maximum current allowed by the bench applied current was more than sufficient to be drawn by the stamp, the motor drivers and the motors.
I am wondering if there is anything that i overlooked for my setup?
I used a bench analog voltage and current supply at 8.4VDC and found that the motors did not respond well to the program i wrote. However, when i lowered the applied voltage to around 6.5VDC, the motors ran without problems (albeit slower than what i desired). Similar results occurred when i used the battery that has the nominal rating of 7.2VDC (max 8.4VDC).
I am puzzled and asked a lab technician regarding this problem and he too could not troubleshoot what was the problem. The maximum current allowed by the bench applied current was more than sufficient to be drawn by the stamp, the motor drivers and the motors.
I am wondering if there is anything that i overlooked for my setup?
Comments
-Phil
Hmmm, the motor drivers are connected at pins 8 and 9 of the BASIC Stamp. Each motor driver can drive 2 DC motors and max current allowed per motor is 2A.
The link to the motor drivers i bought: DC Motor Drivers
The circuit diagram i'm referring to is from a former article. The changes now are the motor drivers as well as the applied voltage is applied at higher than 5V and hence is connected to pin 24. I've attached the circuit diagrams and the current setup that i have also.
Right now the pins 3 to 7 would be used for a wireless receiver and an electromagnet (have not added this in yet). Would really appreciate any input that would help me understand why are my DC motors not running optimally.
My code is listed below:
'{$STAMP BS2sx} '{$PBASIC 2.5} DIRS = $f0ff 'Pin I/O. Input = 1, Output = 0. Electromagnet PIN 3 HIGH Electromagnet 'Motor Driver Input Pins MotorDriver1 PIN 8 MotorDriver2 PIN 9 'RC Pin RCLeftMotor CON 5 RCRightMotor CON 6 RCSubmerge CON 4 RCElectromagnet CON 7 'RC PULSIN variable [Taking in reading from Remote Control Pins and storing them to a variable] PWLeftMotor VAR Word PWRightMotor VAR Word PWSubmerge VAR Word PWElectromagnet VAR Word i VAR Word 'Remote Control Center Constant Values JLeftMotor CON 1905 'Justify left motor joystick. Low = 1368, High = 2476. JRightMotor CON 1883 'Justify right motor joystick. Low = 1500, High = 2315. JSubmerge CON 2022 'Justify submerge joystick. Low = 1454, High = 2572 JElectro CON 2042 'Justify electromagnet joystick. Low = 1470, High = 2580 '#Write to EEProm to detect restart eepromvalue VAR Word READ 0,Word eepromvalue WRITE 0,Word eepromvalue +1 '------ Start of Main Program ------' Main: PULSIN RCLeftMotor,1,PWLeftMotor 'Getting inputs from pins. Pin, State, Variable PULSIN RCRightMotor,1,PWRightMotor PULSIN RCSubmerge,1,PWSubmerge PULSIN RCElectromagnet,1,PWElectromagnet PWLeftMotor=PWLeftMotor & $FFFE PWRightMotor=PWRightMotor & $FFFE PWSubmerge=PWSubmerge & $FFFE PWElectromagnet=PWElectromagnet & $FFFE 'DEBUG CR, DEC PWLeftMotor 'DEBUG CR, DEC PWRightMotor 'DEBUG CR, DEC PWSubmerge 'DEBUG CR, DEC PWElectromagnet IF (ABS (PWLeftMotor-JLeftMotor)>225) THEN SEROUT 8,1, ["2f9",13] ELSE SEROUT 8,1, ["2f0",13] ENDIF IF (ABS (PWRightMotor-JRightMotor)>200) THEN SEROUT 9,1, ["2f9",13] ELSE SEROUT 9,1, ["2f0",13] ENDIF IF (ABS (PWSubmerge-JSubmerge)>275) THEN SEROUT 9,1, ["1f9",13] ELSE SEROUT 9,1, ["1f0",13] ENDIF IF (ABS (PWElectromagnet-JElectro)>500) THEN SEROUT 8,1, ["1f9",13] ELSE SEROUT 8,1, ["1f0",13] ENDIF 'IF PWElectromagnet<=(JECenter+350) THEN ' i=0 ' HIGH Electromagnet 'ELSE ' i=i+1 ' IF i=3 THEN ' LOW Electomagnet ' i=0 ' ENDIF 'ENDIF GOTO Main-Phil
It's the 2 red wires that are connected from the top of the breadboard. They are connected to the VCC terminals of the motor drivers.
Hmmm, for SEROUT command, the input is the baudmode and not the baudrate. I converted the via the SEROUT command from the manual. With 115200 baudrate, 8 data-bits/no parity, true and driven. This should work out to be 1.70, which i truncated to be baudmode of 1. I do hope that this is correct. It's my first time attempting to DIY a robot.
Actually i have bought a battery which has a rating of 7.2V and 3300mAh, because i felt that approximately 7.2V would drive my DC motors optimally (fast enough to provide motion for the robot). The wording on the DC motors indicated 12V and 2.5Amp fuse which i gather would be the respective maximum voltage and current allowed for each motor.
Also, a value of 1 for your baudmode will not get you anywhere near 115.2 KBaud. 2 would be closer, but even that will be off by 30%. What you really need to do is change the baudrate of the motor controller to a lower value that the BASIC Stamp can handle accurately.
-Phil
Phil, would it be wrong to use the VCC of the BASIC stamp instead of the VDD? Right now i've connected the diode as well as a capacitor (100uF) to the VCC. As for the motor driver, i believe that there's nothing much i can add to the motor drivers themselves? I tried having and without the capacitor between the GND and the VCC for the motor drivers and it did not affect any outcome. I have attached an updated photo of the setup.
Also, regarding the motor drivers, i found out that i overlooked the fact that the motor drivers only require a VCC, a ground and the input from the BASIC stamp. The 5V pin is strictly a regulated output pin. Hence i have taken out the wires from the 5th and 6th pin on the right side of the motor drivers.
So from this, i can gather that the most likely cause of my problem would be the baud rate of the motor driver?
The baudrate thing mystifies me a bit, though. I'm amazed it worked at any voltage, but it should certainly not be voltage-dependent.
-Phil
Thanks to both of you! Really appreciate the inputs. I'll try it tomorrow when i get back to the labs. If I can't get the problem resolved then i'll have to stick with a battery rated 6V and compensate with a lighter robot. :depressed: