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.
This week I pulled out and trimmed a couple of the planks that rubbed badly and things seem to be running smoother. I also did a test run with the wall set to 30° overhang. Aside from the climbing being really hard (I seriously need to buy some holds with texture) it ran pretty well.
On the back side of the wall the chain was dragging on the cross members (due to the previously discussed lack of a track on the back side) but it wasn’t noticeable. I still think I will try to fix this in the near future, just to prevent undo wear on any components.
I am very impressed with how solid the thing feels with the wood in place. I had added more bracing to the design after playing with just the frame, but now I think I will take it out.
BUT when I put the wall back to vertical the damn thing seems to stall before ramping up to full speed. I’m not sure what the problem is but I’m guessing it is just a tighter fitting plank binding. I guess we’ll see.
Planks are finally on. It took a lot of planing and sanding, but they are on.
After getting the planks on I was anxious to start climbing. I looked around my garage and realized: I don’t own any climbing holds. I could have mooched and borrowed holds but I thought it would be faster to just start screwing whatever crap I had laying around my garage to the wall. Morgan also volunteered some scrap wood to the effort.
Here is a gif of my first, low speed test. And yes I realize my choice of climbing pants is around 15 years behind the times. Or you can see the full video in all its glory. Most of the noise in the video is from a crane across the street, not the wall.
My initial thoughts are that the whole thing runs pretty well and feels solid. It squeaks a bit but a little more wax in the tracks will fix that. (I need to find some bee’s wax. It, apparently, is a better lubricant for wood.) The chain isn’t spaced perfectly on some of the planks which leads to thumping noises as they go over the drive sprockets. So I will be pulling off those planks to adjust their fit.
I do wish the whole thing was about 6″ taller just to lend a little more buffer when you are climbing, 12″ would be even better. I don’t think you would be able to make a wall any shorter than my 9′-2″ ceilings usable, unless you made it permanently overhanging. If I were to start from scratch I would knock a hole in the ceiling and have the top poke into the attic.
Running at ~30° overhang would let you fit the track portion of this wall under an 8′ ceiling, which would still be usable. So there are options for this to work with a lower ceiling.
After all the trouble it took to make the planks I would consider laminating 2 layers of 3/4″ plywood together to make the planks or trying 1″ plywood. This would eliminate the issues I had with twisted boards, bowed boards, and varying thickness. So it would remove labour from modifying boards while adding some by requiring gluing them together. I suspect it would lead to a better end product though. You would be able to use cheap plywood for the back layer and better stuff for the outside and it will make it easy to countersink the t-nuts so you can used the standard bolt for a given climbing hold. AND you could ensure that all the planks would fit snugly in the guide channels so they wouldn’t feel wobbly without any sanding.
Additionally, in the future, I would try including a track on the return side of the wall as well as the climbing side. This would keep the planks running vertically, and prevent the chain from rubbing on the crossmembers in the wall regardless of chain tension and wall angle. It could be a looser fitting track to keep friction down. I think this addition would make it easier to control chain tension and make the unit easier to use. I might try to add this feature to this wall just to try it out.
Next step will be electrical design. First, I think I will just purchase a prefab stepper driver, power supply, arduino etc and get this wall running as a stand-alone unit. Later I think I will design a custom board with everything on a PCB, maybe add some whizzy features like wifi so you can control it from your phone.
Lastly, I want to mention how impressed I am with my Bosch cordless rotary hammer (this one if your curious). I had only intended to use it for putting up routes, but my corded drill wasn’t suitable and I ended up using my hammer drill for everything on the planks. So it drilled around 150 t-nut holes (1/2″ x 1.5″ deep) and sunk around 150 1.5″ decking screws on about half a charge.
If you are shopping for a drill for route development this one is light enough for drilling on lead at 6.25 lbs and will punch more than a dozen 3/8″ x 3″ holes in moderately hard limestone per charge. However, if you only plan to bolt on rappel I would consider finding a heavier drill with a bigger battery (more Ah) to get a few more holes per charge. I am considering buying a bigger battery for this one; bosch makes compatible batteries with almost 3x the capacity.