Hi Folks, I'm hoping I could get some suggestions for how to build a linear actuator with the following specs using OpenBuilds parts: Total travel at least 60 mm Total/max length of the assembly/actuator (in the axis of travel): no more than 130 mm Velocity of at least 15 mm/sec The unusual aspect concerns loads. In normal operation the required force is tiny, maybe a 10 N (~ 2 lbf), but it needs to resist backdriving up to about 1000 N (~ 200 lbf), and be able to survive that force transmitted in through the actuator in its motion axis. Loads off of this axis should be minimal. I'm imagining a configuration something like this, with a stepper motor parallel to a lead screw/track, connected via a worm gears. I'm assuming I'll source the worm gear and motor separately, so I this is mostly a question about the recommended parts to support the load and dimensional requirements. Thanks in advance! Dan
Gentle bump here. Would be happy to have some feedback about the form of the question. Is it too vague? I've been thinking of building my design around this architecture: C-Beam Linear Actuator Bundle. Would the components use in that design be able to withstand 1000 N (~ 200 lbf) in the actuation direction? Bushings, leadscrew, etc? Thanks, Dan
No, the kits from this site won't go anywhere near that level of force. You'll need something far more industrial. Pneumatic actuators might also meet your requirements.
Thanks Rick. Just to be 100% certain we're talking about the same thing, I only need 10 lbf from the actuator, but I need the parts to be able to withstand about 200 lbf (back-driven). I'm assuming that the worm gear etc will provide adequate resistance to back-driving. Are you saying the kits can't provide 200 lbf force, or that they couldn't withstand a 200 lbf load? Dan
I'm not sure how you're separating the forward force from the back force but let's just work with the back force as a static load. That 200 pounds is being resisted by a single 5mm set screw in the lock collar. You can probably overcome this weakness by using a Tension Nut - OpenBuilds Part Store but be sure and include a washer below it to spread the force to the outer raceway of the bearing (assuming you are using a radial bearing) such as not to trash the bearings. The next weakest element would be the lead nut. The weakness here is the Delrin nut block and the two 5mm screws holding it to the gantry plate. With the two screws having standoff spacers, it is likely the screws will flex and bend, causing the nut block to bind. If you can somehow brace the back edge of the nut block to resist the movement that would be induced by the forces it might be workable. I can't comment however as to whether the Delrin nut block will handle the 200 pound load. I don't know as anyone has ever tested it. And finally the last obstacle to overcome would be eccentric loading on the gantry plate. If you can keep the force at the plane of the face of the gantry plate, it might work. But if there is any eccentricity caused by the force being applied to an arm extending from the face of the plate, with that amount of force you will likely peel the upstream wheels out of the V-groove. The 5mm bolts that serve as the wheel hubs can only handle so much force. I would suggest you consider linear rail bearings and ball screw style lead screws, as this will greatly increase your chance of success. Also using a less aggressive (lower pitch) lead screw will decrease the issues you will be having with the back force load driving the screw.
Hey Rick, Thanks very much -- this is exactly the kind of information I was looking for. Much appreciated. FYI, the general plan was to use a worm gear to drive the lead screw. My understanding is that worm drives generally have much lower efficiency when back-driven than in the forward direction, so the max back-driving force is correspondingly larger than the force the system can provide in the forward direction (e.g. https://www.geartechnology.com/ext/resources/issues/0393x/simonelli.pdf). Best, Dan
