I need to design some fairly simple gearing mechanisms for a small project. I’m thinking I’ll need some 3D CAD software, but I also want something that could simulate the mechanism itself, to ensure that it works properly, before I build it. I figure something like that must exist, but I don’t know what to search for. Preferably, I’m looking for something I can run under OSX or Linux. In particular, a good CAD app which is less fancy than Autocad.
I’ve done gear simulations using CAD and Autodesk’s animation software. Sure, it’s useful for generating an AVI of your mechanism, but it’s also going to cost you more than most desktop computers and arguably more than your mechanism. In addition, most “simulations” require you to have solved them on paper beforehand. They rarely take into account axle friction, motor torque limits, or angular momentum of the parts – and those are the things that will make an otherwise great design fail when built.
If it is “fairly simple” then you should be able to sketch it out and have someone with mechanical engineering training take a look at it and tell you whether it will work. Head to a local university library and check out a book on linkages or mechanisms, or better yet, go over to their mechanical engineering building and offer a small bounty for anyone who’s willing to help you solve a problem. A senior undergraduate or a grad student should be able to spend no more than an hour and give you an answer, unless it’s a hideously complicated machine.
Alternatively, if you’re mechanically inclined yourself, buy Lego pieces and/or motors that will simulate your design. If the holes don’t line up perfectly with what you intend to build, consider mounting them in a stiff cardboard housing. While the gear ratios may not be exactly what you’re looking for, you can do an analysis to show that with your real gears in place, the output speed would meet your requirements.
If you don’t mind sharing, what’s the project? Do you have sketches or blueprints that you could scan in and post for us? This back-of-the-envelope stuff is my cup of tea. I’ve got a degree in Mech. E., and thousands of hours’ experience building real and Lego gearboxes.
It’s a simple pendulum clock, with a few extra bells and whistles. (I realize that cheap pre-built mechanical movements can be purchased. I’m doing this for fun.)
The gear ratios and such are fairly straightforward, and I plan to buy some small generic gears to use, but the escapement wheel, pendulum and pallets will need to be custom made. That’s why I want to test my design before wasting money at the machine shop. (And, of course, I need an accurate set of drawings to give the machinists.)
Wow! I helped a friend design a clock that was wind-powered. We have not built it – my job was simply the blueprints – but for the escapement and pallets I recommended that he use a circular saw blade and cut his pallets from a relatively hard wood. You could make your prototypes from thick cardboard or heavy foam board, or even from plywood. A razor knife or a jigsaw will suffice to make these prototypes.
The concentric shafts on the clock face will be an interesting challenge (but by no means insurmountable). You will probably need access to a machine shop regardless, and you could save yourself some money if you could find an undergrad willing to do the work for you in the “student shop” of his department. Obviously the Machinists’ Union (to which the department’s machinist most likely belongs) will not be pleased if he hears about this, so don’t go asking any professors.
The design I made was predicated on very little machining – that is, using parts straight from stock such as those available from McMaster-Carr – but still looked like it was going to cost him on the order of $500 in parts. Good luck, and feel free to send me an e-mail if you’ve got other questions.
A circular saw blade! Now that’s ingenious. Might be a bit big, though.
The concentric shafts won’t be much of a problem, I’ve already got some steel tubing of various diameters for that.
I’m off to look at saw blades now…
You might want to look at using copper, Delrin, or some material other than steel for the inner half of your concentric shaft problem. Steel on steel has a horrible coefficient of friction.
As for the saw blade idea, thanks! I thought someone else might have tried it before and went Googling to see if they recommended any particular brand. I didn’t find any recommendation, but I did find several very nice saw blade clocks. Probably not what you had in mind. :smack:
Anyhow, best of luck!