Hi! We are planning to use wheels in our elevator system for lifting the platform consisting the grabber. However, considering the motor weights and the whole grabber system we doubt that the grip of wheels might be insufficient to lift the system. We also thought of a system that the platform climbs using the wheels mounted on it. So there are are two options: First the wheels will be mounted on the grabber and the grabber itself will climb through the supporting aluminium columns. Second, the wheels will be mounted and in a fixed position. Then they will rotate and push the system upwards or downwards like the grabber of Bison Robotics. What do you think about it ?
Answer: You really don’t want to use just wheel friction here.
You have three basic options for doing something like that.
- Rack and Pinion. A flat strip with gear teeth (the rack) and a standard gear (pinion), drive the pinion to move the carriage.
1a) Use a chain as the rack and a chain sprocket as the pinion.
1b) Use a timing belt as the rack and a timing belt pulley as the pinion. - Leadscrew/linear actuator. Exactly what it sounds like, use a leadscrew or linear actuator to move the platform (in the system you’re talking, it’s usually called a “carriage”).
- Cable lift. Basically just use a standard elevator, run some extra cable up to the carriage.
There’s a couple of other possibilities as well, but those are the three main ones. I would say that 90% of teams will go with option 3. Most of the rest will aim for some variation of option 1. A few will go with option 2 and later regret it.
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100% Just to add to this. Gravity and Friction are the enemy not your friend I never recommend anyone use only gravity or friction for anything. My old mentors used to always joke what happens if gravity is off that day? But it’s good advice
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If you really don’t want to do the standard chain or cable (or dyneema) rigging for your elevator, then I would also recommend the rack and pinion system.
Your main problem will be in finding the correct rack and pinion for the what you want to do if you can’t machine them yourself. If you have a CNC machine, of course, you can cut both elements from something like HDPE and get exactly what you need. Otherwise, you’ll need to find an appropriate set with matching pitch and pressure angle. McMaster-Carr has a selection, as does Grainger, but for both your choices will be limited to either steel (heavy but very strong) or plastic. Plastic is probably sufficient for your needs on an elevator, but you’ll need to choose between acetal and nylon, with the second probably a better choice. Even so, you’ll have to adapt the pinion gears, since you won’t find them with hex bores, and find a way to make them work with motors or shafts to supply power.
As you can see, this is possible but has some challenges, especially if you have to buy stock racks and pinions. We did use a system like this (though with steel) as the main lifting elements of our Hab 3 climber for 2019. It certainly worked (and well, once we solved a couple of problems) but that was a different problem than a straight-forward elevator. You might want to take another look at how most teams rig elevators before you commit to this kind of solution.
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