Ok, I see! What do you want to put on the planes? The upper box, during its rotation, could go into collision with the object that you'll put on the second floor (second box). The same problem is even for the second box that collides with the objects in the first floor. Have you studied the trajectories of the boxes during their rotational movement? Have you considered a sort of envelop space? Once you have this space you have to be careful not to put objects in it. I hope you understand me...i'm so sorry for my english.
Yes there is no issues regarding the boxes trajectories. Little 3d printed object will showcased at the end of each box. No possible collisions between them and the boxes (I admit it is not easy to see that in the 3d view) I am more concerned about the movement transmission from the steppers and the choices of the bearing. do you think I could use slewing ring as shown in my previous message?
Yes there is no issues regarding the boxes trajectories. Little 3d printed object will showcased at the end of each box. No possible collisions between them and the boxes (I admit it is not easy to see that in the 3d view) I am more concerned about the movement transmission from the steppers and the choices of the bearing. do you think I could use slewing ring as shown in my previous message? what do you mean by "envelop space"?
For "envelop space" I mean the space interested by the trajectories of the boxes during their rotational movement. About the slewing bearings, first of all you need to define your transmission system. Once you have the forces, you can choose the right bearing. I think your application require just a simple ball bearing....the slewing ring is too expensive. Usually the slewing ring are used for heavy loads.
thanks PierArg. I do not really know which transmission to choose... do you have an idea? gear? or pulleys? I found a stunning piece of art, which is kind of a huge robotic arm. one base is supporting all the moving arms. How do you think it is made? what kind of bearing are used? http://vimeo.com/22001314
Hi thomas, I cannot open the link. Appears the error "page not available" Could you find something similar on youtube? To choose your most (or best?...what is the correct word?) suitable transmission system you need to do some consideration: - price (is the most important....) - what is the reduction ratio you need to realize? - how much space is available in your machine - rigid (for example gears) of flexible (pulley-belt)? I think, but don't give importance on what i'm going to say (first you need to verify the feasibility), you could use a pair of gears.
If I understand what you're trying to do, each of the boxes can be supported by the preceding box. The bottom box supported and attached to the floor. The second box attached to the first but eccentric to its rotational axis. The third box would then be supported by the second box and rotate about an axis that is eccentric to both of the preceding boxes. If this is correct then the boxes provide support and the steppers on provide rotation up to 360 degrees of each box from its starting position. The outer race of bearings such as Kydon Bearings (http://www.kaydonbearings.com/) can be secured to the preceding box with the inner race secured to the moving box. Done correctly, the bearings will allow a good amount of offset load. If I understand what you're trying to do, each of the boxes can be supported by the preceding box. The bottom box supported and attached to the floor. The second box attached to the first but eccentric to its rotational axis. The third box would then be supported by the second box and rotate about an axis that is eccentric to both of the preceding boxes. If this is correct then the boxes provide support and the steppers on provide rotation up to 360 degrees of each box from its starting position. The outer race of bearings such as Kydon Bearings (http://www.kaydonbearings.com/) can be secured to the preceding box with the inner race secured to the moving box. Done correctly, the bearings will allow a good amount of offset load.
Hi Thomas Your title, "Hollow shaft stepper," caught my attention, as did your note that you're on a student budget. Those two situations don't go together. As a student, and even as a stuck engineer, I often try to plagiarize. (As my best mentor said 30 years ago, "Imitation is the sincerest form of flattery.") I like that people are suggesting offsetting the motor from the axis, and appreciate what Randall is doing, pointing you to available hardware. I would suggest copying a bicycle headset (which lets the handlebar turn). Find drawings (online) or disassemble a junkyard bike. The shaft is hollow, as you need, and the bearings are substantial. The inner and outer tubes can be cut and threaded from water pipe using a lathe, and can be shortened or lengthened to fit your needs. You should be able to beg a bicycle repair shop for a useable cast-off headset (the bearing parts). That would give you a strong hollow-shaft bearing set for about $10. Buy a pair of appropriate gears... I think you're dealing with relatively low torque, so you have options. You could try for overstock parts stores (Silicon Valley and perhaps elsewhere), or you could try WM Berg Co online. Center the shaft-side gear onto a lathe and open the hole to fit your shaft. This would be a very good opportunity to try a press fit between gear and shaft, but I'd back it up with a tough epoxy. Mount the mating gear to your motor, and locate the motor to mesh the gears. It's a stepper... you want minimum play at the gears. Adjustability would be a good thing. I hope this gives you a few ideas. Cheap need not be ugly. Stretch your imagination.
I believe that the steppers in the lower box and the eccentric axes are not self exclusive. The initial shafts can be eccentric to the lowest box and the upper shaft (eccentric to both the lower and central boxes is driven by gears or a belt from the inner of the lower shafts. I hope this makes sense and I have already started to fabricate a "copy" of that which you have explained using two 1 rpm clock motors as it seems like a rather nice kinetic art project.
I fully agree with John. You can even recycle some components of old or broken devices. For example, if you have an old printer you can extract the steppers. Or if you have an old washing machine you can use its elecric motor...ok, it is not a stepper but with the right transmission sistem you can obtain the round speed you need. But I think first you need to write down a simple mock-up with one or more solutions. So you can start to define better the single parts of your project.
