A quick update: I did more testing last night after adjusting a plank and managed to get the wall up to 10ft/min; a very reasonable climbing speed. Ultimately, i would like to get it running up to 15 or 20ft/min.
I suspect that the stalling issue I had recently was due to a change in temperature as much as issues with the planks. Basically, the small, low torque motor I am using only has to overcome the friction in the gearbox. It doesn’t need to really drive anything, but when the temperature drops and the oil becomes more viscous that drag in the gearbox increases.
At 10ft/min the motor is turning at 600rpm, and having a torque curve like the one below, I am guessing it is putting out, at most, 200 oz*in of torque at that speed. So very little torque.
I think my options for dealing with this are: lower oil viscosity, use a lower ratio gear box, or a higher torque motor. The use of a lower ratio gearbox might seem counter intuitive but if we go from a 60:1 gear ratio to a 15:1 ratio the motor will be at the same operating point and the wall will be moving much faster. Since the motor isn’t really driving the wall, it just needs to overcome the friction in the gearbox, which will be comparable, this should work. In the end I will probably end up trying all three options.
The 60:1 gearbox wasn’t my preferred choice when I was designing the thing i was hoping for 20 to 30:1 but it was at princess auto and it was cheap. I guess this is what happens when you compromise on your design.