Help with DC motor

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Help with DC motor

Postby samuel » Tue Dec 13, 2011 9:05 pm

Hi,

I have purchased two SPG30-60K DC motors from your company...I would like to ask why the dc motor is not rotating when the supplied voltage is much more lower than the rated voltage (12V)? This voltage range is between -1.8V to 1.8V. I need the DC motor for PID positioning control, and my dc motor must be able to operate between +10V to -10V, which is the signal generated from the PID algorithm. If the dc motor is unable to rotate within this range (-1.8 to 1.8), the control system won't be able to work properly.

Please let me know if my explaination is unclear.

Please advice. Thank you very much.

Regards
samuel
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Re: Help with DC motor

Postby robosang » Wed Dec 14, 2011 1:35 pm

12V rated, how can you drive with 1.8V?? I don think that is possible :D

Try maybe 6V should be able to kick start.
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Re: Help with DC motor

Postby samuel » Wed Dec 14, 2011 2:47 pm

Hi,

Thanks for the reply.

Actually the project I am doing is a positioning system. I use dc motor as the actuator for the system and potentiometer as the feedback sensor. The motor rotation is controlled by PID algorithm.

So, for my case, I will give a set value to the algorithm input, and the controller will try to control until the process value is equal to the set value ( for my case, it will move to the set position). This process is a subtraction process (set value minus process value)and thus the control signal/voltage to the dc motor will keep decreasing when it is approaching to the set position. My problem now is if my dc motor is unable to rotate below 2V, so it means my system won't be able to reach the set position since it will stop at around 2V.

Please advice. Please let me know if my explaination is unclear. Thanks

Regards
samuel
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Re: Help with DC motor

Postby royalstorm7 » Wed Dec 14, 2011 11:35 pm

hi samuel...
...as alternative u can use a servo that operates based on PWM signal...which is much more simple way to control the mechanical position...

tq
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Re: Help with DC motor

Postby samuel » Thu Dec 15, 2011 9:06 am

Hi,

Thanks for the reply,

Royalstorm7, is there any servo motor which can be driven by normal voltage? I thought all the servo must be driven by PWM signal? Please correct me if my concept is wrong thanks.

Besides, I just realized that I can amplify the controller magnitude (Adjust the P, I and D) so that the signal to the dc motor will be big enough to overcome the friction when it is approaching the set position. But this is just my assumption, can anyone please verify my hypothesis???

Thank you very much.

Regards
samuel
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Re: Help with DC motor

Postby royalstorm7 » Thu Dec 15, 2011 9:46 am

hi samuel...that the way of servo motor in action....PWM signal only apply went the internal circuit is there to decode the modulated PWM to the final propotional voltage....check this link
http://www.cytron.com.my/viewProduct.ph ... 4&name=PID Motor Controller
tq
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Re: Help with DC motor

Postby royalstorm7 » Thu Dec 15, 2011 10:09 am

this link can give u a better picture...
http://www.pyroelectro.com/tutorials/se ... motor.html
tq
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Re: Help with DC motor

Postby samuel » Thu Dec 15, 2011 12:28 pm

Hi,

Thanks for the reply.

Can I still use DC motor? Why the DIY project you have shown me can use DC motor in its positioning control. Its condition should be similar to mine, how do they solve the problem that I have mentioned in the previous post?

Please advice, thank you very much.

Regards
samuel
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Re: Help with DC motor

Postby royalstorm7 » Thu Dec 15, 2011 1:52 pm

hi samuel...yes u can use dc mtor by setting the minimum output of your driver to the minimum operating voltage of the motor with the respective load....let say the value is 7.5volt at PWM 85%....so dont fire ur PWM under that value in operating mode unless u want to stop the motor...

tq
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Re: Help with DC motor

Postby ZaM » Fri Dec 16, 2011 1:34 am

maybe you can use motor driver(L293D) + optocouplers(IC-4N-25 )
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