View Full Version : Motorized rocker for tray developing

10-Mar-2017, 07:12
I started shooting X-ray film and developing the negatives in trays got old pretty fast so I've been working on a motorized rocker to make it all a bit easier
Made from some wood sheets, some 3d printed parts and a windshield wiper motor.

I have not tried it yep so we will have to see if it works alright, maybe it's not enuff of a rocking motion.

Here are som pics





And a short video


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

10-Mar-2017, 07:42
this is awesome! I might place the tray on a slight diagonal to get more randomness, or add a little eccentricity to the cam.
I think the concept is sound and your implementation is relatively frugal and elegant, nice work!

10-Mar-2017, 09:29
If it doesn't work out, then use it as a platform for a kitty litter box. If you hate cats.

10-Mar-2017, 11:39
Thank you.
I was planning on rotating the tray some during devloping to add some randomness

This is how the cam looks now and any suggestions on improvements is highly appreciated


10-Mar-2017, 13:18
I'd be tempted to slow the motor to about half the speed; it looks as if the fluid is mainly moving in place rather than moving across in bulk.


10-Mar-2017, 14:31
I do have a speed controller which I intend to use to set whatever speed I want

10-Mar-2017, 14:40
I have a couple motor driven drum spinners. Randomness is assured by having one eccentric wheel, the other a uniform dimension. If this hint does not help I will try to find time to draw it up.

...and thanks for putting up with my earlier wise-crack.

Eric Woodbury
10-Mar-2017, 16:09
It needs to run slow enough that it isn't near resonance. You could cut you rocker speed in half by using a circular wheel and offset the center of rotation.

What's your motor? Is that a car window motor?

10-Mar-2017, 17:06
When I was at RIT in the 1970s, remember seeing several random agitation rigs.
From what I remember:
They held up to 3 16x20 trays.
They used 2 rotating oval cogs at 90 degrees to each other and placed at opposite ends (right and left)
The rocking motion was way slower that you'd expect, and way less than you'd expect.
"Board" under the trays was either Plexiglass or gray PVC.
Wish I had taken a picture of the rigs....

11-Mar-2017, 12:03
Thanks for all the feedback
I am going to try it with a more square wheel to give some more time at the end of the rocking motion.
This combined with a offset center might be the way to go?


If you have any other ideas please share an I will try and test them.

Deane Johnson
11-Mar-2017, 15:41
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
12-Mar-2017, 01:15
These two sites may be of some help designing a motorized agitator:

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

12-Mar-2017, 03:59
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.

12-Mar-2017, 04:46
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
12-Mar-2017, 10:51
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.


bob carnie
12-Mar-2017, 11:34
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
12-Mar-2017, 22:11
That looks better. Adding a couple of random bumps might help prevent a standing wave.

Jerry Bodine
12-Mar-2017, 22:31
FWIW just another idea: here’s a screen shot of a mechanism concept I threw together in MS Excel.