Minimal Mechanical background- Want to design a rotating wood column - Page 1
Forum section: electronics / projects

author: chimera_786
author_rank: Regular Contributor
timestamp: September 18, 2015, 02:06:45 am
content: Hi there! I'm an electrical engineer and want to design the mechanical portion for a rotating wooden column.I have been searching online for all alternatives and I haven't been able to stream line the process. I didn't know which forum/internet location would be best to gather the relevant info and figured I can start here.Requirements:Rotate a rectangular column (10 inches tall, 4 inches wide and 1 inch thick) 360 degrees using a motor. I eventually have the plan to achieve the rotation with a stepper motor. I have attached a the picture of the column and the entire set up depicts a 4 bar linkage (it wasn't obvious to me for design but worked out)Right now, I am having a hard time understanding what pieces will go together to achieve that. I assume I will need a gear set (spur gears, a motor etc).So, what I am looking for (from this post) is a direction which can sort of map out what steps and materials I need to this done. I understand that I don't have enough detail in this post but that's only because I am not sure how to phrase the right questions.Hopefully, this will get me started.Thanks for looking!

author: sarepairman2
author_rank: Frequent Contributor
timestamp: September 18, 2015, 03:07:49 am
content: what is this "wood" material that you speak of?You can make a good enclosure by using PCB panels.by mechanical do you mean a relay or switch?

author: chimera_786
author_rank: Regular Contributor
timestamp: September 18, 2015, 03:13:10 am
content: no. Using a stepper motor, a gear (set) and attach that to the column. Then rotate that.

author: singapol
author_rank: Frequent Contributor
timestamp: September 18, 2015, 03:43:25 am
content: I'm not an expert but a electronics hobbist and have some experience in metal machining. From the looks of your contraption made of wood it's not that difficult to do what you want. The trick is to find a cheap and easy way to attach it to the motor shaft. Using gears is just one method and I think just a liitle complicated and costly. The main thing is the attachment to the motor shaft which is normally round or at least have a portion that is milled flat to enable a screw or a keyway to have a better grip.Firstly the size of the stepper motor I would guess is a Nema 23 or 34 which would have enough torque to take the loading, maybe a smaller nema 17 one could do the job too which cost less.Next will be the attachment/ coupling method, the easiest and cheapest way is to fabricate or adaptsomething like ( imagine the bottom or base portion of a microphone stand, it has a flat plate and a hollow column. Fom there getting a tube that fits over the motor shaft with a hole drilled and tapped for a screw to lock to the shaft and you are in business. The rest is the attachment to your wooden base which there would be 3 or 4 holes for self tapping screws to lock the plate to it. Then mount the motor under a wooden table or another stucture if you want to put on top a table. PS you may need an extender column or longer one if there is any obstruction like mounting under table.For help and resources you can go to CNCZONE which have changed ownwers and go by another name. Other places/webs you can go are the machine building sites, hobby train/ engine sites and cnc router ones that have relevant information that can be useful especially the links to sources of materials like the gears and metal parts that you may need.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: September 18, 2015, 03:53:08 am
content: Are you looking for precision or speed, or just make it go round? Conceivably you could plunk your column right onto the stepper's shaft. You would probably want to pick up a brass hub or something you could bond with epoxy into the column.Chain drive or timing (cogged) belt are another two easy ways to trade RPMs for torque. Gears tend to be a bit pricey and require closer tolerances, but they will work if you want to use them.Ready made reducers are usually kinda pricey. Maybe something from hobbyking I don't know about. Automationdirect has some reasonably cheap worm drives ($88) but they're kinda gigantic as they fit a 56C Face motor. 'Course you could conceivably use a window winder or seat adjuster motor from a car as you can get those really cheap. The problems with them are they're a little hard to interface with mechanically and they're not designed to run full duty cycle. They draw a lot of current too.Stock Drive Products is pretty good for gears, cogs, belts and stuff:https://sdp-si.com/And of course mcmaster carr.sarepairman2: apparently it's a dead tree carcass!

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 18, 2015, 04:39:09 am
content: It seems likely that what you are trying is to position an operation over a region centered on your "column", with r-theta positioning. You want to rotate the platform to the appropriate angle, and then will use your four bar linkage to achieve a radius.If that is your intent, you aren't interested in continuous rotation, but are interested in precision, and probably in speed and force. Worm drives are good for force, and also generally can't be back driven so you can turn off control when you get where you want to be. They are slow though. They are one extreme of a trade you will have to make between speed and force. Gear trains and belt systems can be used to implement these trades, and people spend semesters at university learning the ins and outs of these selections. Google will get your feet wet.This brief discussion will give you some idea why the people on this forum want to know more about what you want to do. It will help them narrow down the universe of possible suggestions to something manageable.Also - Wood is a widely available, inexpensive, easily machined insulating material with a wide variety of equally widely available and inexpensive fastening and joining systems. It does have drawbacks such as porosity, dimensional instability and being subject to attack by a variety of biological agents from mold to termites.

author: ez24
author_rank: Super Contributor
timestamp: September 18, 2015, 04:48:57 am
content: Is this a signature pen?

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 18, 2015, 05:41:20 am
content: 3cents idea... gtg..

author: chimera_786
author_rank: Regular Contributor
timestamp: September 18, 2015, 12:40:34 pm
content: @MechatrommerThe 3 cent idea is what I had come up with as well..(sort of).@ CatalinaWOI think i understand how you have interpreted the idea. Its slightly different than that.The whole method of operation is: have the column rotate every 72 degrees. The servo will work the 4 bar linkage (see attached) and then the column would move another 72 degree and the servo will do its thing till the 360 degrees is complete. The purpose of the armature is still being defined but the movements are pretty much constrained. That should help narrow down the choices.@Paul MoirYeah, just make the column go round, every 72 degrees, till 360 degrees are complete. I understand the gears are expensive but I think if I pick the right one to do the job, it'll be worth the investment.So, how's this for a game plan:1- mechatrommers drawing seems like a workable one. It needs to be adjusted to become practical.2- I choose the stepper motor I want to work with. The power rating of the motor doesn't need to be a whole lot as I am only turning the column (and minimal assembly weight of the 4bar linkage).3- From there, I figure out what size gear i need. I have been reading up on gear selection and yes, its not easy to pick one but cant be too hard either. I guess the question is: What size gear do i need? As in, what gear ratio do I need formed, when the gear is connected to the motor. I don't need to reduce speed as it'll be from a controller stepper motor. From there I can sort out what should be the DP, FW etc for the gear4- From there, I then figure out what type of shaft coupling/linkage I need to fit on the motor shaft. Most probably it'll need to be a pinion to move the selected gear (3).I think it has narrowed down the design approach, however feel free to point out what I have missed.Thanks for looking

author: mjkuwp
author_rank: Unknown
timestamp: September 18, 2015, 12:52:40 pm
content: budget? Are you making just one of these?Cordless drills have gearboxes in them and there are also 90-degree cordless drills and these have DC motors that presumably you could control. With that solution you'd need an encoder for feedback and some controls. Steppers are more straightforward.

author: chimera_786
author_rank: Regular Contributor
timestamp: September 18, 2015, 03:53:27 pm
content: I'll be making a few of these. Probably around 10. But thats if the design worked out and then i could think about cost shavings.I actually am trying to work with a stepper so that with a predictable start point (calibration everytime to find a hall effect sensor), i wont need to close the loop on it.As for my previous post, I really don't want to under-estimate the torque limit on the motor (and Im trying to figure out how to go about calculating the required torque).The mass needed to be moved is:1- The column2- Servo3- 4 bar linkage5- Attachment to the arm.

author: G7PSK
author_rank: Super Contributor
timestamp: September 18, 2015, 04:22:57 pm
content: If it only rotates one direction, I would just put an index plate on the bottom with 5 slots and use a solenoid with a pawl to pull it one notch at a time or use 10 slots and have the solenoid operate twice each time you want the column to move 72 deg. The index plat could be cut from plywood.

author: robrenz
author_rank: Super Contributor
timestamp: September 18, 2015, 04:40:56 pm
content: If you tell uswhat you are trying to accomplish with the mechanismyou may get much more valuable information that could save you a lot of wasted time and money.

author: chimera_786
author_rank: Regular Contributor
timestamp: September 18, 2015, 05:19:47 pm
content: @G7PSKI might be mistaken here but wouldn't the solenoid be more work to get it up and running,and running smoothly? Sounds like it might be. One motor, one gear, revolving shaft is seems a lot simpler.@robrenzThe mechanism (as I have stated in my previous posts) is to have the column move, counterCL, 72 degrees, for a total of 360 degrees. At each 72 degree mark, the (already designed and working) servo mechanism will move the 4 bar linkage. I dont think I have any newer information to provide past this.

author: G7PSK
author_rank: Super Contributor
timestamp: September 18, 2015, 05:40:29 pm
content: What you would get is precise angle of movement, no gears and motor with no requirement for feed back to any electronics, the actuator could be powered by anything including steam as all that is required is a linear pull.

author: chimera_786
author_rank: Regular Contributor
timestamp: September 18, 2015, 06:18:17 pm
content: I need 5 discrete movements. So 5 solenoids. They'll add up >$100 (plus the added system weight). I can search around for cheaper ones (old used ones) but they still weight a lot no?Motor solution: One heavy device, 1 spur gear, shaft and a couple of low cost support hardware etc.

author: ez24
author_rank: Super Contributor
timestamp: September 18, 2015, 06:44:22 pm
content: Quote from: robrenz on September 18, 2015, 04:40:56 pmMy guess this is an alarm clock. It will rotate over thevictimsleeper and poke them in the eye to wake them up.It is obvious the OP does not want to tell us what he is making.There is someone on this forum designing something that rotates accurately. He tried printing out markings with a laser printer and seems now to be working with the optics from a mouse and an etched scale. Sorry I cannot find the post, maybe someone can help. I think he is making a pick and place machine? He may even have posted a pdf of the markings. He is going into great detail.Edit: The other OP just posted. So here he is:https://www.eevblog.com/forum/projects/cheap-recognition-pick-place-reflow-oven-solder-machine-for-tiny-pcbs/?topicseen

author: chimera_786
author_rank: Regular Contributor
timestamp: September 18, 2015, 07:49:22 pm
content: haha. you mean the end application for the contraption? Lifting magnets and depositing them on the adjacent one. Small enough that their weight will not hit the motors torque rating.But this doesn't bring me any closer to solving the mechanical issue. Although, I have found the path forward. I want to do the stepper motor assembly with gear to move it.A couple of reasons: less parts to move (solenoid solution needs to be repeated 5 times for 5 discrete events) and a cool learning experience.

author: robrenz
author_rank: Super Contributor
timestamp: September 18, 2015, 07:53:03 pm
content: Quote from: chimera_786 on September 18, 2015, 05:19:47 pmThat tells us nothing about what those motions are trying to accomplish. What are you trying to do at the end of the 4 bar linkage?Edit: I posted this before your post above

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 18, 2015, 07:56:57 pm
content: from the look of it, the linkage will move up and down (almost vertically) parallel to the column. to pick up something or draw a dot on a paper. his only concern is to rotate the main column i guess. maybe quite similar to robot arm base rotation...

author: ez24
author_rank: Super Contributor
timestamp: September 18, 2015, 08:09:11 pm
content: Quote from: robrenz on September 18, 2015, 07:53:03 pmQuoteSo depositing them into the sleepers eyes?Seems difficult and from your picture they are not "depositing". ie easy to lift but difficult to deposit (being a magnet). Don't you need a non-magnetic "grabber" to pick them up and release them otherwise seems they would stick to each other like in your picture, thus another control.So this is some sort of pick and place like the other post.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 18, 2015, 11:48:50 pm
content: Read the solenoid and pawl suggestion more closely, and then use the inexpensive organic computational device. ONE solenoid is required for this column. It can provide precision indexing, requires no search to find zero (although you might want to sense the zero location in case your controller loses track of 5 pulses or has to start up after a power outage.)I really like the idea, wish it was mine.

author: chimera_786
author_rank: Regular Contributor
timestamp: September 19, 2015, 03:15:08 am
content: @ CatalinaWOWOkay. I'll look at this suggestion more closely. I haven't really played around with solenoids before so it'll also serve as a "check" for learning new skill sets.I haven't either come across a pawl+solenoid config and a quick youtube search showed how it can be used. Essentially, the column would be mounted to ratchet/index plate and solenoid will pull the ratchet every time and hence turn the base.I'll look into this more as it might actually be another alternate route to go. BTW, there isnt a lot of straight forward info an index plate. Can you point to a few?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 20, 2015, 02:14:02 pm
content: An index plate is simple, so probably not addressed often. At its simplest you would have 5 holes drilled in your base (in a circle around the pivot). In your rotating part you would have a spring loaded ball at the radius of the circle. It would act as a detent stopping your tower at the desired location.A variation, or improvement on this basic idea would be to create a ramp along the circumference of the circle leading down to each hole. Then the solenoid would need only displace the tower from the current hole, and the spring would drive the tower on to the next.There is obviously a large design space here, with trades on solenoid stroke, power and geometry, along with the geometry of the index plate, friction and the detent mechanism (a spring driven wheel might be more desirable than a spring load ball for example). Other index plates merely have notches around the outside of a disk and have a simple flat spring with a knob on the end as a detent. This approach would make the "ramp" concept easier to implement. While it may take a lot of thought to work out the details, the end result is a cheap, simple and reliable device.