DIY Motorized roller base

[Henrim]

Thanks Everybody!

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.

Yes, thanks that retainer idea is probably a better idea. The tank I have is a Multitank 5 two reel tank. It is slightly conical but that is compensated by positioning the rear wheels tad higher than the front ones.

[Henrim]

Spent some time today breadboarding the user interface. Tried to keep it as simple as I can.

The UI consists of a LCD display, two push buttons and a rotary switch.

The LCD shows the chosen development time and once the machine is running also the elapsed time (or countdown maybe).

One push button is used for starting the machine and the other one is used for switching the LCD background light on/off.

From the users point of view a rotary encoder acts like a potentiometer. The difference is that it does not have a start or end, it rotates indefinitely. The encoder is read digitally and in this case it is used for setting the development time. By turning the knob seconds can be set from 1-59. Minutes are set by pushing and turning the knob. I first thought about using two encoders, but it seems to be ok to push and turn the knob. It takes about two full turns from 1 to 59. Going clockwise time increases and going anti-clockwise time decreases. Rather quick.

That should be it for now. Rotation speed and agitation will be constants and if I need to change them I do it in the code and re-flash the micro-controller. If I ever find that I need to change those on fly I will add a few controls to the machine.

Here's the breadboard:

[jeroldharter]

Excellent. You might consider putting the front rollers on some sort of liver (like the front of a wooden field camera) so that you can accommodate longer drums.

[Dirk Rösler]

This is great. My approach would be to drive the roller base, not the tank like a Beseler Uniroller. That way, you don't have to worry about the tank to motor coupling and also you can roll tanks of all sizes, incl. expert.

[Henrim]

Excellent. You might consider putting the front rollers on some sort of liver (like the front of a wooden field camera) so that you can accommodate longer drums.

Thanks, that would definitely be a good idea.

This is great. My approach would be to drive the roller base, not the tank like a Beseler Uniroller. That way, you don't have to worry about the tank to motor coupling and also you can roll tanks of all sizes, incl. expert.

Thanks Dirk, that was my initial thought too and I will do that if I decide to make an other version (I still have four roller skate wheels left!). The reason I went with the coupling was because I wanted to do something quickly I did not have suitable round aluminium stock to make a rim to the driving wheel. The point is moot though because I could have done the rim from POM as I did the coupling... But that was my thinking that night Another reason would be that if I ever want to make a water bath it would be easier by driving the tank.

[Dirk Rösler]

Great! Would be great if you could share a basic diagram so we can try to build one ourselves

By the way, are you basing the reversal on time or number of revolutions (could also vary with a bigger drum)? Perhaps time is easier, esp. if RPM is constant.

[Henrim]

Great! Would be great if you could share a basic diagram so we can try to build one ourselves

No problem sharing. Other than the fact that I do all the thinking by prototyping so there are no diagrams But I'll try to document this a bit in the end. I have different kinds of stepper drivers but the one I'm using here is a very straight forward and simple EasyDriver.

By the way, are you basing the reversal on time or number of revolutions (could also vary with a bigger drum)? Perhaps time is easier, esp. if RPM is constant.

That is a good point. Right now I'm concentrated to this one particular tank so I can get my development going. But that's definitely something to think about. The good thing about driving a stepper motor with software is that fundaments like this can easily be changed at any point.

[Jac@stafford.net]

The roller bases I have use slightly eccentric driving wheels that makes the tank rock gently, presumably to eliminate streaking.
.

[Ari]

The roller bases I have use slightly eccentric driving wheels that makes the tank rock gently, presumably to eliminate streaking.
.

I had thought of that too, as I use a Simma-roller which has that feature.
Perhaps it would be as simple as replacing two of the wheels (one diagonally across from the other) with slightly larger diameter wheels.

[Henrim]

The roller bases I have use slightly eccentric driving wheels that makes the tank rock gently, presumably to eliminate streaking.
.

Good point. I expect that everyhing is slightly out of tolerance so the feature will be there naturally