lift bridge

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roadshark
 
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Joined: Sun Nov 29, 2015 5:53 am

lift bridge

Post by roadshark »

Hi Bill, I hope you and family are well and you are getting in some winter cycling! I am still constructing the lift bridge and have now built the deck and the two towers The weight of the deck is 130gms. To lift the bridge six cables are tied to each end of the bridge. The cables go over a wheel and then drop through the tower and are attached to a counter weight. The motors (using 2 stepper motors) are used to pull the bridge deck down and the weights lift the bridge up when the motors reverse.
Would I be right in my thinking that the weight of each counter weight should be around 70gms?
I have never heard the motor run on the real bridges. I assume that the motors would need to develop some speed before the bridge starts to lift. Do you know if they use phases or some sort of clutch? THX.

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adafruit_support_bill
 
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Re: lift bridge

Post by adafruit_support_bill »

Hello Mr. Shark. Haven't had much of a winter this winter, but getting plenty of miles in.

You are correct in that the sum of the mass of your counterweights should be about the same as the mass of the deck.

As for motor control, you will want to achieve a smooth "jerkless" acceleration as the deck begins to move.

Not a lot of implementation detail here, but they do mention variable frequency AC drives: https://hubbellcdn.com/catalogfull/High ... ec2020.pdf

In your case using steppers, I'd do something similar by gradually ramping up the step frequency to produce a smooth acceleration curve. The easiest way to do that is using the AccelStepper library. https://www.airspayce.com/mikem/arduino/AccelStepper/

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