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Startracker design questions - Jamey - 09-10-2017 09:57 PM

It would appear that the greater the distance between the hinge and the drive rod the faster the drive rod will need to turn, and the longer it will need to be? Is that correct?

Do you think there is any increase in tracking accuracy by making this distance (between the hinge and the drive rod) longer? (Ie the drive rod has to turn faster, and travel farther, meaning more steps of the motor for a certain time period.)

Also, there is an inherent error in "barn door" designs known as the "tangent error". Does the arduino code compensate for this? If not, do you think accuracy would be increased by using a curved drive rod? Or using a "corrective cam" as I've seen on some designs?


RE: Startracker design questions - jpedroc - 09-12-2017 04:12 PM

(09-10-2017 09:57 PM)Jamey Wrote:  It would appear that the greater the distance between the hinge and the drive rod the faster the drive rod will need to turn, and the longer it will need to be? Is that correct?
Yes. Correct
(09-10-2017 09:57 PM)Jamey Wrote:  Do you think there is any increase in tracking accuracy by making this distance (between the hinge and the drive rod) longer? (Ie the drive rod has to turn faster, and travel farther, meaning more steps of the motor for a certain time period.)
Yes, it will increase the accuracy but the system will get too large to hold the camera + tripod in balance (from my experience). Right now meets the compromise between size and accuracy, but the larger, the better... Sleepy

(09-10-2017 09:57 PM)Jamey Wrote:  Also, there is an inherent error in "barn door" designs known as the "tangent error". Does the arduino code compensate for this? If not, do you think accuracy would be increased by using a curved drive rod? Or using a "corrective cam" as I've seen on some designs?

Using a modern camera, you will need only 200 seconds (TOP) of exposition (ISO200-300). For that time, the tangent error is negligible. This error becomes a problem when the angle is over 15ยบ (if I recall it properly, I made the calculations time ago)

The tangent error can be corrected via CODE but will narrow down the options of creating the STARTRACKER using another physical elements... Will just work for certain dimensions and rods metrics.


RE: Startracker design questions - Jamey - 09-16-2017 10:35 AM

Thank you for your quick reply! One last question - I may have to order the drive rod from Amazon - how long, at minimum, does the drive rod need to be?


RE: Startracker design questions - jpedroc - 09-17-2017 11:35 AM

You are welcome ;-) 12 cms at least