If you use individual gears I guess you then have to be very precise in putting them together and I wonder if it wouldn't be better to "customize" a ready to use gearbox like this one http://www.gnchobbies.com/single-gearbox-4-speed.html
Did you ever had similar needs? Which was your preferred choice?
Thanks a lot!
If you're going to go with Tamiya products, probably their best option to get the speed you need would be their planetary gearbox; it has a ton of ratios, and you just add or subtract the units needed.
Most of time, for my projects, I just buy a gearmotor with the speed of gearbox I need - there's a ton of examples out there (new and surplus); the only drawback is that some of the "new" ones can be pretty pricey (I once busted a gear in the gearbox of a motor I had bought surplus - I contacted the manufacturer, and they said I could either purchase another motor/gearbox new from a distributor - for about $120.00 - or purchase the gear itself, but I would have to buy 50 pcs minimum - at $7.00 each! This was for a small gearmotor I had bought surplus for $10.00).
One of the other things to keep in mind for a gearbox is what the load is going to be; sometimes cheap "hobby" gearboxes of the Tamiya variety might not be up to the task, and you'll need to look into more expensive options (ie, metal gears).
Building your own gearbox should only be done if you have the means/skills to make fairly good precision assemblies; alignment of the gears can be fairly critical to keep noise and wear to a minimum (more noise and wear means less efficiency, higher current draw on the motor, more wear on the motor, etc). It could turn into an exercise in frustration, unless you need something really specific for the task (ie, you need something to fit somewhere an off-the-shelf solution won't go).
Thank you for the great answer! That was exactly the kind of advice I was looking for. I have to admit I always looked at gears and chains as trivial mechanical issues, but now a new world opens up in front of my eyes.. Also a world where, like I find in your experience, I think I couldn't afford a car if I had to buy its individual pieces ..
Anyway, I made my mind to give Tamiya's kits a try even if, considering I plan to reduce a stepper motor, I guess some careful adaptation will be unavoidable.
emainorbit:
Thank you for the great answer! That was exactly the kind of advice I was looking for. I have to admit I always looked at gears and chains as trivial mechanical issues, but now a new world opens up in front of my eyes.. Also a world where, like I find in your experience, I think I couldn't afford a car if I had to buy its individual pieces ..
Anyway, I made my mind to give Tamiya's kits a try even if, considering I plan to reduce a stepper motor, I guess some careful adaptation will be unavoidable.
Something to keep in mind is belt drives are easier solutions for many problems, although they can have slippage; they are more tolerant of slight misalignment issues as well. Slightly less tolerant, but still easier to build than a geared system, is a cog/timing belt design. The next level would probably be chain and sprockets (like on a bicycle). Then gearboxes. Each level is less tolerant of misalignment and low-precision than the last; that is also the scale of cost of parts (that is, a belt-drive system is much cheaper to construct than a gearbox).
Shaft mis-alignment can be compensated for by compliant/flexible couplings (on the low-end, a simple piece of rubber tubing or hose can be used; on the high-end - double-u-joints, or for high speeds, CV joints).
Ultimately, whatever power-transmission method you build should be selected, designed and built as accurately and precise as your skills and tools will allow for, to get the best results.
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