DIY Motorized roller base

[Henrim]

Hi,

I got myself a Jobo 2500 tank and a 2509n reel couple of years ago and tried to use it in upright position like I would use a smaller tank with 120 film. That was rather cumbersome with the big tank so I have been developing sheets in a tray since. Which is fine, for a sheet at a time at least.

Anyway, this week I thought about trying the big tank again and decided to hack a roller base for it. Did it from material I had in hand. Old roller skate wheels and a piece of plywood and so on. While I was at it I thought why not attach a stepper motor and a driver to it. I milled a mount that attaches to the bottom of the Jobo tank. A stepper was used because I have them and have experience with them.

The driver is controlled with an Arduino. I quickly tested the gizmo this evening and it's working as expected. I just need to add a stopper to the front of the tank to prevent the tank from sliding of the wheels. And then I need to make a simple user interface to set the development time on the machine.

I tested with a piece of code that changes the direction after each revolution. The motor was running at around 30rpm. Now I would need to figure out what would be a good starting point for the speed and how often to change the direction. I have no experience with any processor machines so I would be grateful if someone who has would give me a pointer.

Cheers,
Henri

The machina


The mount

[Ari]

Beautiful job, Henri.
My Simma-roller runs a 25xx tank at around 30-32 rpm, but I don't know if there is a standard speed for these things.

[Kirk Gittings]

Nice!

[polyglot]

Lovely. I use a lift on mine and therefore the cog for drive, but I believe that when no lift is involved, there is usually a big circular magnet glued on the base of the tank. The magnet couples to a similarly big magnet on the motor drive, and that's what keeps the tank from floating away.

I know you can buy the Jobo magnets, so that's probably the best way of mounting your tank to the drive.

In terms of speed... I think 50rpm is the recommended speed for doing 120 in a tank like that, and probably a similar speed for the 2509. A bit slower won't really hurt and I'm sure 30rpm will serve fine. Does the stepper have enough torque to not skip (many) steps when reversing the rotation and with 1L of water in there? It's not hard to do a little acceleration ramp though.

And if you're super-tricky, you'll put the whole base on a servo-powered tilt for the purpose of dumping the tank after a programmed interval, with a solenoid for filling it

[muihlinn]

Jobo ATL speeds are 75 rpm for 1500/2500 tanks, 50 rpm with expert drums. Changes direction each 4 turns or so.

[Henrim]

Thanks a lot Ari, polyglot and muihlinn and Kirk!

I now have good starting point to try out and actually develop a sheet!

Lovely. I use a lift on mine and therefore the cog for drive, but I believe that when no lift is involved, there is usually a big circular magnet glued on the base of the tank. The magnet couples to a similarly big magnet on the motor drive, and that's what keeps the tank from floating away.

I know you can buy the Jobo magnets, so that's probably the best way of mounting your tank to the drive.

I was thinking about magnets and it would probably be the best solution. For now I think I will just install a V-block in front of the tank with two ball bearings that touch the tanks neck. Like so:

Does the stepper have enough torque to not skip (many) steps when reversing the rotation and with 1L of water in there? It's not hard to do a little acceleration ramp though.

I had about 1L of water inside the tank and it skipped a few steps when reversing. Though I was driving the motor with rather low current so it would help giving it more juice. Anyhow I tried adding a 100ms delay between the change and that helped. So it would work ok by just quickly easing out the speed to zero and then change the direction. The motor is a NEMA23 mount so it is easy to change it to a one with more torque if needed. Not sure about the exact spec of the one I'm using but it has a lot more potentiality than what I used yesterday.

And if you're super-tricky, you'll put the whole base on a servo-powered tilt for the purpose of dumping the tank after a programmed interval, with a solenoid for filling it

Yeah. Will see about that

[koh303]

very cool!

[jon.oman]

Very interesting!

[Graham Patterson]

I'd have thought that a horizontal wheel at the tank lid would work as a retainer, maybe lightly sprung. The problem with the smaller single 2509 reel tanks is that they are distinctly conical. But if you are prepared to use the larger tank you won't have that problem. It is an elegant solution.

[koh303]

I'd have thought that a horizontal wheel at the tank lid would work as a retainer, maybe lightly sprung. The problem with the smaller single 2509 reel tanks is that they are distinctly conical. But if you are prepared to use the larger tank you won't have that problem. It is an elegant solution.

Are you referring to the 2520 (multitank 2)? If so, they are all perfectly cylindrical, just like all other modern Jobo tanks.