Hi Everyone,
I am looking to use my Arduino to control a valve that I have on my chamber. By turning the bolt with a fine thread the lever goes up and down which controls the flow.
I was thinking that I could screw a gear onto the thread and then use a nut to secure it in place. I then could use a stepper motor like adafruit sells to turn the gear and I'd be on my way. The problem is that the thread is a 1/4-56 which has been absurdly hard to find online and on top of that it seems hard to find gears that have the central hole tapped for screws. Am I missing something or what is the best way to connect to this shaft? Alternately I could just connect the motor directly to the shaft instead of a gear, but I can't find the right fastener for the job. Thanks a lot for your help!
connecting the motor directly to the shaft is easy i did a similar project myself but it depends mine didnt need high torque
and i think connecitng the motor directly to the shaft is alwasy easy and hackable
Thanks for the quick responses! You probably have the right idea that me trying to find the proper thread is a losing battle. Now that I've posted once, I can include a link of what I am talking about:
http://www.mdcvacuum.com/urd/uniface.urd/ecf0030w.display?315010
I certainly could file the edges down on the end of the shaft so I could bolt a coupler on the top. Currently I open and close the valve by turning the two disks that are locked together. As an alternative, I wonder if I could get my machine shop to drill some holes that I could then bolt a cog onto. (Heck, maybe I could just have them tap a coupler that would work here.)
I am not exactly sure how many foot pounds of torque I need, but it certainly isn't a lot. I frequently open and close it using just 2 fingers. Do you think that these small adafruit stepper motors (27 mNm) would do the trick or is there a beefier motor that someone would recommend?
I was thinking about having feedback based on a +5V trip that is sent out from my pressure gauge, but I'm not sure how necessary it is because the valve is very consistent in that it needs exactly say 2.5 turns to open each time. That's why I thought a stepper might be a good idea, but I could always have a DC motor that I just turn on for a period of time before stopping it.
Do you still think that the DC motor + a coupler is the way to go or is there a better suggestion? Thanks again for your help!
Probably several ways to approach the issue. You may be able to thread a piece of rubber tubing onto the adjustment shaft and clamp tightly to make a connection part for the shaft. If you need a nut type of adapter, oil the shaft (so the epoxy nut can be removed) and then mold one on the shaft using an epoxy like JBWeld. A large servo modified for continous rotation and controlled by the arduino with position or pressure feedback might be a motor solution.
Hi again,
You are probably right about the stepper motor not having enough juice. I was thinking about using a rigid shaft coupler that they have on that servo city page possibly with a rubber sheet to be a little nicer to the threads. I think that the 1/4" would probably due the trick. I was thinking of preventing the motor from turning by mounting it directly to the lever arm and that should prevent the angle differences that might arise otherwise.
The site also seems to sell DC motors and I was thinking about going with the 4.5 rpm one because from what I can tell "finger tight" is about 1 Nm which is about 140 in oz. Since the torque I am applying should definitely be less than that I should be fine with the 688 oz in. for the 4.5 rpm one.
I should then be able to power this off a power supply and control it using the adafruit stepper motor board and then just use the external terminals they provide and remove the jumper. Does this seem like a sane plan or am I missing something? Many thanks again, you all are lifesavers!
Be aware that stepper motors need to be "calibrated" to a known position if not being controlled by a feedback loop.