This is a small stepper I got at Tanner’s. The spindle is about 1/8" and has the gear attached at noted. I want to attach this stepper to a propane gas regulator. I won’t bother you with the other project details until I get it going as that is subject to some debate ion its implementation. I just want to get this part going for now.
I believe the stepper and regulator knob are compatible re torque as the regulator is very easy to turn and multi-turn. (I have a digital gas pressure transducer on the input and output side of the regulator. My question is more of a mechanical nature.
I may not even be removing the gear but do you think the gear has been ‘pressed onto’ the shaft? If so would the gear have a tapered hole? Or perhaps there is some sort of glue that has been used. Would you remove the gear with a punch while supporting the gear somehow?
Any thoughts on interfacing the motor to the regulator. The regulator knob does not want to some off with gentle prying and doesn’t unscrew then it reaches its counterclockwise limit. But I don’t think I have to remove the knob to do what I want. My first experiment does not have to be so robust. I may just create some sort of epoxied notch on the regulator handle and a key on the gear, like a screw and screwdriver. For longevity, I guess I would want perfect alignment of the stepper and regulator shaft, but that can come with a subsequent revision if it makes it that far.
I realize there are other issues here, like either establishing some sort of rotation encoder or a limit switch and / or mechanism to determine the end point(s) of rotation.
Just playing with this for now, but give me your thoughts on any of this and I’ll post any progress here.
hackaday video - interesting! Sort of how I am needing to regulate, but I need to actually regulate the pressure and sense it electronically for finer control, so I’ll mess directly with the reg and not a downline valve.
And thanks, Glenn, who suggested looking for a screw under the label of the knob.
I’m afraid ver 0.1 of this will have some wonkiness until it can prove to be worth more effort. You know how that goes. My first thought was indeed to print a 3D part to both join the two devices and to hold them in place. I need to learn the quickest 3D rendering package and attend the 3D print tutorial to get up to speed on that. (But I’m really excited about being able to print parts) I looked at Blender and realized that it was more than an afternoon to even get started on that software. I realize there are other 3D design programs . . . a whole 'nuther thread indeed!
So one option here would be to lathe an aluminum cylinder, drill holes for shafts on each end and then drill and tap holes for set screws. Any other thoughts on this approach for joining the two? The reg does have large flat areas on the spindle. Might be a bit complex to machine a matching part. Once again . . . 3D printing !?!?
Just watched a tutorial of sketchup. Since the motor and valve will be held together with a frame, it should be pretty simple to create a cylinder with an area on one end to mesh loosely with the gear and then fit precisely on the notched regulator shaft. The regulator shaft moves inward significantly as it is turned so I’ll give some thought to how to handle that. Just excited about learning the skill of 3D printing to solve a design problem.
Joseph - that would be exactly what I would need to remove the gear. I’ll check the numbers when I get home.
Slow night at work. Been playing with Sketchup. Here are some clips from a lame attempt to come up with a 3D part. Have to learn how to clone and rotate components to make the gear part. Not working so well. Also I’m trying to make offsets and push down edges to remove volume on the small end on the notched end and I’m left with a sort of shell I can’t get rid of, but just need to spend some time learning.
If you don’t need fine control over the rate of flow there are solenoid valves that can be had for as little as $7 (designed for propane and methane use) that would be reliable, safe, not a kludge. If you decide to use the stepper the pressed gear can be removed.
The shaft coupling that Frank suggested is probably the best mechanical way to attach the regulator to the stepper motor. Not sure if that’s the right size though so measure everything if you go that route.
Thanks those adapters would be quite rugged and allow for some issues with alignment - sort of like a limited U-joint. I may wait until a future revision for that degree of durability.
And re removing shaft - good video - alternative to gear puller. I do have some gas solenoids from Ebay, 12V powered. I thought about PWM gas control! This is for a sort of oven, so it would work, but be noisy and might wear out the solenoid. Another technique used on some older anesthesia ventilators for bellows drive gas is to have a combo of PWM on a series valves that deliver a binary sequence of flow rates. Ex, five valves deliver gas into a manifold at 16, 8, 4, 2 and 1 LPM respectively and thus can achieve any flow rate from 0 to 31 LPM.
I played a bit more with Sketchup, mostly as an exercise to learning it for 3D printing and came up with this part. Would depend on the other parts being fixed in order to stay put. I hope to play with it today and may get up to DMS today this evening.
I’m sort of getting the hang of Sketchup. It’s tricky using a 2D mouse to define a 3D space.
Well darn. I defined a solidworks model for you so you could just change a few values and get a perfect fit. The site won’t let me upload it. It’s probably because I am a new user. Well anyway, any reason to model in solidworks is a good one. If you are making hard edge parts versus organic models (ie. gears vs zombies) I’d recommend a parametric modeling program. The nice thing about a parametric is one can just change some numbers and your model will adjust itself in the way you told it to. With other methods one has to redraw the changes. Solidworks, Inventor, Solidedge, ProEngineer, and Catia are all examples of parametrics. Since the space is a non-profit you will be able to obtain Autodesk Inventor for free. If you are interested in the model I made just let me know. I’ll find a way to send it on to you.
Thanks, Eric. This is all just a learning experience. I was at the KiCad class today and spoke with lots of folks about different solid modeling packages. Solidworks and Inventor are ones that came up as highly recommended. I think I still have a UT medical center email address. Maybe I can get hold of Inventor or another package as a student.
