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Groo
member

Reged: 03/05/09

Barndoor mount
#6139201 - 10/15/13 02:36 PM

Hello, Does anyone know what rate I would need to increase the gear rotation on a simple straight rod barn door mount to adjust for tangent errors? I would like to use the Arduino to adjust the rotation speed.

Thanks

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Phil Sherman
Pooh-Bah

Reged: 12/07/10

Loc: Cleveland, Ohio
Re: Barndoor mount [Re: Groo]
#6140517 - 10/16/13 09:38 AM

Divide the rate by the cosine of the angle of the hinge where 0 is closed. You could probably get by with a table that adjusts the speed every rotation or two.

It's easier to make a curved pillar block for the rod to push against. This will keep the distance from the hinge to the contact point a constant, eliminating the need to adjust the motor speed.

Phil

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Groo
member

Reged: 03/05/09

Re: Barndoor mount [Re: Phil Sherman]
#6140713 - 10/16/13 11:32 AM

for the curved pillar block how much of a curve is needed? or is it better to try and bend the threaded rod?

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Groo
member

Reged: 03/05/09

Re: Barndoor mount [Re: Groo]
#6140720 - 10/16/13 11:35 AM

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Phil Sherman
Pooh-Bah

Reged: 12/07/10

Loc: Cleveland, Ohio
Re: Barndoor mount [Re: Groo]
#6142598 - 10/17/13 10:15 AM

The big problem with a bent rod is that you can't rotate it. You need to use a captive nut (one that doesn't move as it's rotated) that rotates and forces the rod through it. The advantage of the bent rod in this case is that you can attach a larger disk to the nut and rotate it using a motor that presses against the edge of the disk. The ratio of the diameters between the disk and the motor shaft is a gear reduction mechanism that multiplies torque and, for a stepper motor, increases the step resolution.

The critical issue with the disk is to get it perfectly centered on the nut. It might be easiest to attach it then spin it and trim down the edge so it's concentric with the threaded hole in the nut.

Phil

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