I’m not sure where this question fits in, so I’ll post it in Servo Erector Set. Please let me know if there’s a more appropriate forum. Anyway…
I need to make a large plotter style X, Y, Z style device. I might be able to get away with servos for the up and down Z axis motion, but I need about 20" square movement in the X & Y axis. I was thinking a motor with teeth, like this timing belt pulley.
Will this timing belt pulley fit on a motor, or is it just for servos? If it does fit, where could I find belts that fit it? I was going to use the belts as a track for the X and Y axis. The instruments I need to move around will end up weight about 2 pounds, so I figured motors with some position feedback would be better.
Can you control a motor with the SSC-32, or do I need other electronics? I’m not finding a lot of info on linear motion sorta projects, but I’m probably using the wrong keywords as this is all new to me…
You can probably do what you need just using servos. I’d make a round turntable out of a $3 lazy susan from walmart. Place a servo under it to rotate it 180 or 360 deg. and have the things of interest on top of it. Make a moving gripper on a beam that runs over the center of the top of the turn table to reach the things on the turn table. Probably fairly cheap to make.
I never thought of that, pretty darn good idea. I’d need a large lazy susan to replace the 20"x20" minimum square I was needing to cover. Think a servo would have enough power to turn a lazy susan that big?
I’d also still need the linear movement along the beam for the gripper, or in my case a liquid dropper. I figured a servo could handle the Z axis/up and down motion of the dropper (pipettes actually…), but the linear motion along the beam? Anyone ever built something like this, and maybe shed some light for a nOObie?
you could always use a servo for thismaybe have a tray in tracks and have the servo on board the tray so you dont need to worry about belts or anything, then just have some small lits on the track bottom so that a gear or something could go in there, of just have a little strip of plastic iwht gear teeth on them
Make a rolling cart on the beam positioned by a servo, or make an extendable beam/arm using the brackets and rollers that allow drawers to be moved foward and back. You may need to watch your friend do her thing to get a good idea of what mechanical movement is needed. Operating a pipet might take some creative thinking. A servo can rotate the lazy susan as it would only be supplying rotational force to move it.
I guess I was under the impression that since most servos were 140 degrees rotation that you really couldn’t get a foot or so of linear motion out of one.
I was thinking a good general purpose arm until I watched my girlfriend do her RNA/DNA ratios using pipettes when I realized an arm just wasn’t it. I like the lazy susan idea, and the plotter style X/Y movement. The pipette are going to be difficult, I’m thinking maybe linear actuators, sounds like those are pretty powerful, which would be perfect for operating the tough to push buttons on them, and a nice consistent slow speed.
For holding the pipettes I’m thinking a half-assed molding to sit under the ledge, and then some really tight straps around it. That’s pretty cool that the servos have enough juice to rotate a lazy susan. I don’t think I gave them enough credit for how much power they have. I’d love to use them for the tracks since it would make the position feedback much easier from what I vaguely understand, but I was concerned they didnt’ have enough throw in them to move across a foot+ long track.
For light weight situations, you can gear up servo movement to a certain extent. A servo that has 180 deg rotation with an 12" across disk attached to the servo horn can have ~18" inches of linear pull on a string attached to the edge of the disk.
I don’t think I fully appreciated how powerful these servos are. I guess when I was looking at building an arm, it has to support the weight too, but since this design would simply move the item, and not have to support it the servos would work well. If I need more juice on the rotation I guess I can link together two analog servos on that 12" disk attached to the servo horn.
Just made my first order to get me started, so much for the couple of months of my life. Thanks folks.
After thinking about the “lazy susan” style setup, I like that a lot. I can’t decide if the “table” holding all the trays of test tubes should rotate, or if the frame holding the gripper should rotate. I’m thinking the gripper frame because its weight would be consistent, whereas the weight of all the trays will vary depending on the setup. I like the math too, easy to program using vectors with a rotating setup.
Below is a sail boat winch servo that is made to rotate 3.5 turns instead of the standard half turn. It is also a 1/4 scale size so it has more power than the standard servo. This would be better for operating a shuttle along a beam.
Thanks for the tip, I was concerned about the length of the shuttle run. I did just order two 5645’s today from lynxmotion, just to get started with playing with my SSC-32, but I could use these for my Z axis too. I’ll have to read up on these sail winch servos, hadn’t seen much about these on the site.
Hmm, digging around in the forums I’m not finding much about sail winch servos. Besides the larger size, which isn’t an issue for my application, what’s the cons of these? Heck, what in general is the pros/cons of a sail winch servo? They sound great for my application. Is the accuracy ok?
Servo controllers that use single byte positioning will have 255 or less discrete positions thru the full travel range. If a controller has a wider range of positions, the actual number of descrete positions will be greater, probably depending on the accuracy of the positioning pot in them. I tested a cheap analog servo and got ~425 discrete positions in the ~190 deg rotation that it could do. I haven’t had any experience with the sail servos, but I suspect it would have about the same accuracy over its full travel range.
Hmmm, I just got my 5645’s and they’re a lot smaller than I anticipated. Now I’m wondering if servos is even the way to go for the X and Y axis movement of my system. I decided against the lazy susan design, I think the error will be too great towards the outside ranges, so I’m going to have to come up with some linear sliders that move nice.
Of course I haven’t hooked up my 5645’s yet, so they may be much more powerful than I anticipate, but I’m guessing these and the sail servo might be better used for the Z axis part of my system, and other movements that I need to pull of on the shuttle itself.
Maybe I should use motors for moving the X & Y shuttle around? I do need to go about 20"x20" for an extended period of time. Guess I’m just having second guesses about this, you really think servos (i.e. the quarter scale sail servo) could handle moving a 2 poundish shuttle around on rails?
If I need to use motors, are they accurate enough? I’d assume I’d have to add an optical encoder or something and read the values back in through my phidgets interface card. How do you control these, errrm, motor controllers? They don’t look like they have serial or usb ports. I do have a phidgets interface card on my computer, can they be activated with the digital outs on those?
Anyone use one of these before? It actually mentions using it for X-Y tables like I need to do. I never new Trossen made a stepper controller. Unfortunately I know nothing about motors, so I Can judge the specs to tell if it’s anygood, or a good deal. Anyone?
nema 17 size motor is pretty small, and you probably should know that as stepper motors increase in speed their torque falls off quickly unless you are running them from a fairly high supply voltage, which in turn requires more complicated electronic$. unless you use a half decent micro-stepping drive, stepper motors frequently have both some audio squeel and mechanical resonance issues that make for interesting problems.
you really should consider the track or table system you need in some detail and be able to come up with a good ballpark on the amount of linear force or rotational torque it will take to both start moving and then continue to do so. this will allow you to make a motor/actuator/gearbox purchase decision from a more informed standpoint and eliminate fustration at it always stalling or the expense of something way oversized for the need.
The more I read about stepper motors the more I’m thinking they’re not worth it. I guess if I need more power to move the table shuttle around I can just use multiple analog servos per axis and use a “y” servo cable adapter like in the aluminum tubing arm assembly guide. One or two of those sail servos with 3.5 rotations of turning should be enough I think for an axis. The shuttle might weigh 2-3 pounds, but the servos wouldn’t be supporting the weight, just sliding it along the track.
I definitely have to build the shuttle part first since it’s the most critical and “highest risk” part of the project. Then I should be able to better figure out the weights involved.
Guess I should get off my butt, hook up them 5645’s and see just how powerful these servo thingies are
Hmmm, how well does the parallel servo thing work anyways? Can you keep adding analog servos, or is there significant diminishing returns when you parallelize servos with teh Y cable? I see that theres that whole servo mid position alignment deal you have to go through…
Ah, screw it. I’ll just get the 805BB’s for the X and Y axis motion, surely those will be powerful enough. Good deal on 'em too. So many toys, so little time…
