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ffej
Experienced Roboteer
Joined: 22 Jun 2004
Posts: 595
Location: Kurrajong, NSW
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Variable resistor = bad idea
The current that the motors draw will quickly burn out just about any variable resistor you can buy from dick smith / jaycar. All their talking about there is servo switching.
A better way of servo switching is to pull the servo's apart, keeping the servo and trimpot intact. You then take the output of the servo, and use it to drive the base of a transistor which then drives a relay. This also requires the use of a filtering cap (about 100uf will do) between the resistor base and ground to filter the output of the servo (which is PWM) an extra 12V battery (you can use the main bot battery at 12V if your really skimpy on weight, but its not reccomended) and a 4K7ish pulldown resistor.
Assuming the servo is trimmed to neutral, when you push the stick forward, one side of the servo lead goes positive, the other negative, and when you push it backwards, the opposite happens. If you attach a transistor to the side that goes positive, it will turn on and allow the power to flow from the battery to the relay coil, which is then energized, and the relay allows current to flow through it to the motor.
I can draw you a schematic with exactly how to build a propper bang bang speed controller for your bot ( dual H bridge setup) if you like, or just catch me on msn and ill explain it better there. A plus with this setup is that you dont need a failsafe, as when the servo looses signal, it just turns off, which kills power to the base of the transistor, turning the relay coil power off.
BTW, this is how the controllers on Catalyst and the original version of Singularity worked, except they used hacked up oatley controllers that output the same signal as a servo does.
Theres nothing wrong with servo switching, it works fine, I just hate things that are not solid state when they could be . . .
BTW X2, you might wanna get a V-Tail mixer when you buy that radio, that way you can use one stick to control the bot. _________________ Jeff Ferrara
fb@ffej.net
ffej.net
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Thu Jan 06, 2005 4:59 pm |
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