Heavy lifting with (GASP!) relays!
Gramps
Posts: 117
I like simple and cheap especially when it works better then the high priced spread.
This is a work-around to control big DC motors with a prop or a stamp and a hacked servo instead of an HB-25.
The principle is to power 2 relays (forward and reverse) using the output from a cheap servo.
Feed back was achieved by mounting the servo pot on the motor shaft.
I suppose an encoder like Parallax part 328107 would work for constant motion. (at $40 each, I’d probably take a stab at making a simple encoder from scratch.
We used a Parallax (Futaba) Standard Servo and hacked it like this:
http://forums.parallax.com/forums/default.aspx?f=15&m=458971 (third post)
Results were poor. It worked but the motor was erratic at close alignment of the pots(first test video).
Erco suggested a simple solution, that is, to connect the motor so that the leads were shorted when the relays were off. This created a dynamic breaking effect that really works well! (second test video)
Now we have “shadow bot” with some real muscle!
Test one
erco’s very cool relay circuit attached below..........
Test two
Gramps
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'What is your life?"
"It is even a vapor that appears for a
little time and then vanishes away."
Saint James 61 A.D.
This is a work-around to control big DC motors with a prop or a stamp and a hacked servo instead of an HB-25.
The principle is to power 2 relays (forward and reverse) using the output from a cheap servo.
Feed back was achieved by mounting the servo pot on the motor shaft.
I suppose an encoder like Parallax part 328107 would work for constant motion. (at $40 each, I’d probably take a stab at making a simple encoder from scratch.
We used a Parallax (Futaba) Standard Servo and hacked it like this:
http://forums.parallax.com/forums/default.aspx?f=15&m=458971 (third post)
Results were poor. It worked but the motor was erratic at close alignment of the pots(first test video).
Erco suggested a simple solution, that is, to connect the motor so that the leads were shorted when the relays were off. This created a dynamic breaking effect that really works well! (second test video)
Now we have “shadow bot” with some real muscle!
Test one
erco’s very cool relay circuit attached below..........
Test two
Gramps
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
'What is your life?"
"It is even a vapor that appears for a
little time and then vanishes away."
Saint James 61 A.D.
Comments
1) Dynamic BRAKING:·GOOD! (what your motor·achieved·on 24V in http://www.youtube.com/watch?v=1EKlAOUXZ8U )
2) Dynamic BREAKING: BAD!· (what·my motor·achieved·on 24V··in http://www.youtube.com/watch?v=VmNc_V5jdPE )
erco
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·"If you build it, they will come."
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'What is your life?"
"It is even a vapor that appears for a
little time and then vanishes away."
Saint James 61 A.D.
@Gramps: Any chance of some closeup photos to aid with the instructions for replicating this? Still a little hazy here.
Thanks!!
OBC
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Propeller Feature Projects: PropellerPowered.com
Visit the: PROPELLERPOWERED SIG forum kindly hosted by Savage Circuits.
http://forums.parallax.com/showthread.php?p=893416
and http://forums.parallax.com/showthread.php?p=874406
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·"If you build it, they will come."