Motorized rocker for tray developing

[Deane Johnson]

Back in the 1970's I purchased a home made rocker for sheet film. It had three trays for 4x5 film. It moved slow enough that the fluid flowed to the end, then sort of splashed the other way, thus mixing the chemicals during the process to a small extent.

It worked well, except for one issue that had to be watched. The developing action on the ends of the sheet film was slightly greater than the center of the film, due to turbulence, which of course caused more development on the ends than the center of the negative.

I think it would have been considerably more nuetral if there had been some sort of minor tilting in the 90 degree axis as well.

in manual agitation, I suspect most of us rock the tray end to end a couple of times, then side to side a couple, then back to end to end, etc. It's almost necessary for a motorized rocker to have some of this same action to assure more even development.

[el french]

These two sites may be of some help designing a motorized agitator:
http://www.mekanizmalar.com/menu-linkage.html
http://blog.rectorsquid.com/linkage-...and-simulator/

If you used non-circular cams (or gears) in this one, you would have some interesting motions: http://www.mekanizmalar.com/alternat...imulation.html

[Thalmees]

Marvelous OeT.
Ideas outside technical side:
1. After certain level of maturation and planning of your project, why you do not share it in Kickstarters?.

I can upload the 3d files if someone else would be interested of making their own.

2. What's for forum members interested in buying similar thing from you?
Thanks so much for sharing.

[OeT]

Here is the squared wheel version and it's loking better.
I also added the speedcontrol ond it works alot better at alower speeds



A vid at various speeds

[Martin Aislabie]

The lecturer who taught me photography at University told of a mechanical tray rocking system that had been developed.

However, the reason these mechanical rockers never caught on, was that they would produce uneven development - due to a standing wave developing in the trays.

So - standing waves will develop in a tray if the speed of rocking and the length of time the wave takes to travel down the tray and back, coincide.

Which means anyone wanting to make a mechanical rocker will need to have a variable motor speed controller, to overcome the standing wave problem.

Apparently humans naturally impart random rocking without even realising it.

Martin

[bob carnie]

Lazi Studios in London ontario had a huge darkroom sink with rocking trays, I see no need for them as I am still strong enough to lift the big trays, and as I get weaker I will splash the chemicals on the print like a two year old.

[el french]

That looks better. Adding a couple of random bumps might help prevent a standing wave.

[Jerry Bodine]

FWIW just another idea: here’s a screen shot of a mechanism concept I threw together in MS Excel.

[Watership]

I would really appreciate those tray rocker plans. Thanks, mark