Tony, I suggest trying to design a machine that can be sold and shipped without the water basin. This would make the machine much smaller and lighter to ship anywhere in the world. When buying a Jobo, weight and shipping costs are an obstacle.
Most anybody can find some kind of big water basin, plastic or metallic according to taste. The ideal solution would be something that you put inside this large basin. It will rotate the tank, warm the water, circulate it and maybe provide some kind of rapid change like the "lift".
If you go for this solution (i.e. only selling the complicated parts, not the basin) I suggest considering two separate units: the "baths" unit and the "tank" unit. The first unit, the "baths" unit, serves to keep chemicals and water at the right temperature. You provide thermostat, heater, pump and the user provides the basin.
The second unit has the motor for the tank rotation, and also keeps the tank at constant temperature. That means two heaters and two pumps, but the cost overall (for not having to buy a specific basin, and for saving on shipping) will probably be less. Much greater flexibility would be achieved.
Separating the two units has several advantages:
- No need to design a two-level basin (like the Jobo); users can use common plastic basins;
- Much less problems in regulating the water level around the tank;
- Anybody can adopt it better to the space he has in his darkroom. One could even keep the chemistry behind his back if need be;
- People who need 7 or more baths (including rinsing water) will have a big basin for their "baths" unit. I use 7 chemical baths plus 6 litres of warm water in my E6 processing. People who only need 3 or 4 baths will use a smaller basin and will save space.
- The same gear can be used when people shifts from B&W only to C41, and then from C41 to E6.
- By the same token, if you use a powerful enough motor (don't save on that), people can use it in a little basin if they only use a 1-roll tank or 2-roll tank, and save space. When they decide that they want to try with 6-roll tanks, they will just move the unit in a larger basin.
I also suggest the heating to be made with a digital and precise thermostat, like the Jobo CPP2.
Personally I prefer plastic. It takes more time to go in temperature but, once there, it is easier to keep it at a stable temperature.
Fabrizio