Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: teddy on June 15, 2008, 10:26:41 PM
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Hey, anyone has any idea on how to built a h-bridge and connect it to a Dc motor to power an automated arm that holds a 15-17 inch lcd screen? it needs to be able to move to the user's desired position. In this case, how much torque should my dc have?
I am now doing my final year project. and i really need some help here. Thanks a million! (:
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hello check out this schematic from this site > http://www.societyofrobots.com/schematics_h-bridgedes.shtml (http://www.societyofrobots.com/schematics_h-bridgedes.shtml) for the H-Bridge. Just plug ur 4 outputs from Microcontroller into A, B, C, D. Or u can find chips have H Brigdes integrated. So to make 1 motor go foreward and backwards u need 4 outputs.
But if u dont want microcontroller just use a switch instead of HBridge. Wire the switch so if u press it one way it goes up, other way goes down - simple. Have this hooked up to ur power supply,which will depend on your motors and desired speed.
I would use a gearbox, like a cheap Tamiya one. Probably want metal gears for long life. U cant just stick ur motors onto the LCD, it will spin around a thousand times a second... Worry more about speed than Torque. I guess u would want to design it to lift a force of 1kg at the end of the arm
Torque= Force x Length of Arm. Length of arm is the distance from the rotatingshaft to the point where the Force is acting.
Say u get a motor that has rated 1000rpm and torque of 100g.cm.....
U put that through a gearbox with a ratio of 500:1. So it slows it down 500 times... This gives u an rpm of 2rpm (1000/500=2) on the output shaft. This will multiply your torque however (100g.cm x 500= 50,000g.cm = 50kg.cm) so that will be your torque - Divide this by length of moment arm (lets say 10cm) - 50kg.cm/10cm = 5kg of force. More than what we need (5kg>1kg).
U would probably want an rps of say 0.25 - or 15rpm on the output shaft. So in 1 sec the arm moves 90degrees. Nice and slow for accuracy.
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ok. Thanks alot! but do you have any other recommended sites that i can refer to for my current project? thank you
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http://www.societyofrobots.com/robot_arm_tutorial.shtml
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ok. Lets say if i were to use a SN754410 motor driver. Do i need to programme the driver to move my retarctable arm? or i can just power the arm using a switch? Any recommended sites i refer to for the codes if i need to programme the driver?
Thanks (:
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Or is there any other motor drivers recommended for this project?
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just use a switch
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hmmmm you will need some sort of position feedback (like an encoder or limit switch), or the arm motor won't know when/where to stop . . .