Hello! First-time poster here. I am a newb to this stuff, so bear with me…your advice and input are greatly appreciated.
My project requires a small platform to move at two speeds along a linear path. It would travel to one end, stop, and then very slowly return. At one of three pre-set locations it would pause, wait for a signal, and then return to its origin at the quicker speed.
I plan to use Actobotics parts and Arduino w/motor shield as the controller. I was envisioning a length of channel with timing pulleys at both ends, an XL belt, and a motor driving one of the pulleys. The belt would attach to a slider mount of some kind.
My question: What motor (stepper, servo, gear) is best suited for this job? (I assumed a stepper, due to the positioning needs; but I’m not sure that a servo or gear couldn’t do the same job somehow.) I can provide more project details if it helps.
It would depend on ow complex you want to make it. A regular DC motor would work but would need some calculations to determine when and where to stop and for how long. A stepper would be used if you need more precise movement. Also steppers aren’t known for their speed.
Instead of the belt/pulley setup you might consider using a threaded rod and some nuts fixed into the movable platform. That allows for rather precise and slow placement. (I’ve seen low cost 3d printers use it for linear motion) Aside from a minute amount of backlash the rotation of the threaded rod is directly related to the linear motion of the platform by the thread pitch. But the quick speed might be an issue. Quickly rotating the threaded rod through the nuts would generate a bit of heat in it from friction. So speed limits or lubrication could become a requirement.
Wow, thanks to both of you for the responses and insights. I’m out for the day but will consider all this later. I have some details I can add that might be relevant. Thanks again!
[This and a with a microswitch or optointerrupter at the stop positions can be controlled easily. These motors are really powerful, I have two of them.](FIRGELLI | 12v & 24v Electric Linear Actuators)
Ah, some interesting possibilities. Before delving into them here’s a summary of the application:
The platform carries a small vacuum suction nozzle above a surface to be cleaned. (The nozzle does not touch the surface. Tubing connects the nozzle to a vacuum pump in another location.) Total distance of travel is only about 6” or so. It moves the full distance and stops while the vacuum pump engages. It then slowly travels back (about 15 seconds per inch of travel), vacuuming as it goes, until reaching one of the three possible locations. It pauses while the vacuum stops, and then quickly returns to the point of origin. (Quickly is a relative term. I was thinking about .25 sec/inch; i.e. end-to-end in about 1.5 sec.) By the way, the surface is rotating: it’s a vinyl record of 7", 10", or 12" diameter.
So the scale is pretty small. The smallest actuator jremington linked to (250mm) is in the ballpark, but I like the idea of building something from the ground up— and maybe for less?
A regular DC motor would work but would need some calculations to determine when and where to stop and for how long
I was thinking the controller would time the process. What about sensors controlling the positioning? Along the lines of what lyndon mentioned, I had been thinking microswitches might be a way for the controller to guide a gear motor. Maybe one at the far end would trigger a stop & return at slow speed, until a switch at the target location was reached.
Instead of the belt/pulley setup you might consider using a threaded rod and some nuts fixed into the movable platform.
This would still need a channel or shaft for the nozzle head to travel on though, correct? Either way, It seems like belt or rod are both viable options for transfer. In either scenario, would a gear motor (or the rotary actuator lyndon linked to) be a sensible solution for powering it? I’m leaning toward that, and just choosing whether belt or rod is the way I want to go.
The linear actuator I linked has a screw drive that is normally turned by a stepper motor, so you have extremely precise control over the motion (direction, distance, speed and timing) without any additional sensors or switches. All you need is a very small microcontroller and a stepping motor driver (about US$ 10 for the pair).
Instead of the belt/pulley setup you might consider using a threaded rod and some nuts fixed into the movable platform.
This would still need a channel or shaft for the nozzle head to travel on though, correct? …
Correct, it just replaces the belt for linear movement. But 2 threaded rods could avoid the need of guiding rods/channel/shafts. Assuming their rotation is linked mechanically so it doesn’t jam when one side moves slightly faster. And the platform is light enough not to bend the rods.
With the added information about the setup and intended function it is clear you don’t need the preciscion in placement. But this could be fairly cheap if done DIY.
In most scenarios, unless cost was an overriding factor, I would go with the actuator. And I say this as someone who has a large variety of ball-bearing slides, timing belts, leadscrews, stepper and servo motors and other motion transmission and miscellaneous coupling hardware at his disposal. I have a very well stocked “junk box”
However, the time it takes to properly integrate and align the pieces means that unless I need something I can’t find at a reasonable price, it’s much, much faster to use an off the shelf actuator like the one jremington linked to.
Thanks all—I’m getting a clearer picture of where I’m heading. I like the stepper-driven actuator, and I see that the smallest version jremington pointed to has a c. 150mm range of travel which is what I’m looking for. (The DIY’er in me wants to build vs. going off-the-shelf: but I see the advantages here. Will mull that one over.)
Given my application, any suggestions for a stepper? I’m thinking small given it’s not driving much weight; and the contact-less vacuum nozzle isn’t creating friction or “hold” against the surface. The torque I’m seeing on some steppers seems like overkill.
Well, if you want to DIY so bad, I’ll let you have a ball-bearing slide, a precision ballscrew, timing belt and gears and a small stepper to drive it for $50. That represents over $200 of drive components that are far better quality than that linear stage that was linked to. You’ll get your DIY fix on and I get to clear out some space in the lab.
However, I still think you’ll get to the end faster by purchasing the complete prebuilt stage. Just something else to think about
thanks lyndon, that’s certainly a generous offer. I need to think it over but if I go that route I’ll contact you via a PM. Right now I’m working out the details of a couple other aspects to the project; I want to get them squared away before funding the rest.
jremington, good advice there. (Reminds me of something I’ve heard said before, “determine the problem before finding the solution”.)
Thanks to everyone who’s contributed here, you’ve clarified a lot of my thinking. I’ll report back if I get things working the way I hope to.
