Power to a rotating wheel - Page 1
Forum section: electronics / beginners

author: mribble
author_rank: Regular Contributor
timestamp: March 22, 2018, 05:55:53 pm
content: I have a wheel rotating at about 2000 RPMs. I'm trying to figure out the best way to power a small motor on this spinning wheel that needs to run for 1 second every 15 seconds and draws 50ma at 3-5V while running (circuit draws negligible power). Yes, this motor needs to be located on the spinning wheel and it is not the motor spinning the primary wheel.So anyways I'm trying to come up with the best way to power this motor. Below are the options I can think of and the issues I can see with them.1) AA or AAA batteries - Hard to fit them into existing design. Add weight and care needs to be taken so they are balanced around the shaft.2) Lipo batteries - Need to come up with charging solution. Probably need 2 so I can balance them around the shaft. Spinning these at high speeds makes me pretty nervous and since shipping these batteries in the mail requires extra process I'm leaning away from this option.3) Power through the axle - The wheel axle is already pretty custom so trying to add some brushes and way of delivering the power seems really hard. I'm probably going to be making about 500 of these so I'm limited in manufacturing options.4) Some kind of power harvesting - Perhaps coils on the wheel and magnets on the wheel base (primary wheel is stationary so I could do magnets on base). Other options light getting centrifugal forces could also work. The issue here is I'd still need some say to store enough of this power to move the motor (maybe caps?). This is the option I'm least sure about.So as you can see there are pretty big negatives for any of the ideas I can think of. Do people here have ideas on how this can be done?Thanks for any ideas you folks share!While understanding the reason I'm doing this isn't necessary to help answer my question, I'm sure some of you will be interested in why I'm doing this. I'm trying to add a small motor on the flyer of an electric spinning wheel (converts wool to yarn) that automatically moves the hook back and forth. Here's a video that we made that shows a person manually moving the yarn hooks that I want to automate.

author: Cerebus
author_rank: Super Contributor
timestamp: March 22, 2018, 06:33:22 pm
content: Slip rings is the easy way, but you seem to have already ruled that out.Energy harvesting? Basically this is building a small generator. Building one that mechanically loads the wheel smoothly will be hard, if you don't the wheel motion will become non-uniform and that might affect your thread quality.Inductive. Make a transformer. One coil on the wheel, in the plane of the wheel, concentric with the shaft. Another in parallel on the non-moving side. Feed in AC at a few kHz one side, rectify and smooth on the other. Ideally needs at least a ferromagnetic core (is the shaft steel?), ideally two U shaped half toruses enclosing the coils (e.g. a hollowed out bagel cut in the usual fashion for bagels) to cut down emissions and increate the amount of power you can transfer. Either way your leakage inductance will be high to very high.

author: admiralk
author_rank: Regular Contributor
timestamp: March 22, 2018, 06:43:54 pm
content: They used a simple DIY slip ring for this gadget:https://makezine.com/projects/persistence-vision-led-globe/Basically just a bearing with the wires connected to the inside and outside.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 22, 2018, 06:44:22 pm
content: Interesting project with an interesting opportunity to create a solution.Solution 1:If the spinning wheel is the same or similar to the one in the video, there are possibilities. The wooden end of the large spool is flat, so, why not place a flat coil on the surface that is directly connected to your motor. Or, if you have a PCB with a circuit for control, you could simply charge a capacitor on your circuit to store the charge. On the stationary pedestal, affix a small magnet that is aligned with the coil. Sizing the capacitor to charge in 15 seconds with every pass of the coil to the magnet. If you connect the coil directly to the motor, the motor would turn a small amount with every rotation of the spool, this would eliminate the need for a control circuit. If you need more rotations of the small motor, make multiple coils in series. Would take a little experimentation, but that is the FUN!

author: Ian.M
author_rank: Super Contributor
timestamp: March 22, 2018, 07:17:01 pm
content: Planar slip rings. Get a round PCB made with the heaviest copper you can afford, with annular ring tracks on one side for the number of contacts you need, and a large enough hole in the middle to clear the axle and any custom mechanisms there, then take apart a small DC motor for the brushes, of the carbon 'pill' on a flat leaf spring type, and solder the ends of the brush springs to a piece of stripboard as a carrier. The ring tracks should be at least three times as wide as the carbon 'pill' so you can shift the brushes over to the other half of the same track if it wears excessively. Don't forget to either put vias along the track edges to stitch them to an identical track on the other side you can wire to, or if its single sided, put a pair of pads 180 deg apart protruding past the track edge with a through hole for the wire.If the motor the brushes have been salvaged from is well used, odds are the brush faces wont be flat and will need gentle sanding on fine Wet&Dry paper to flatten them before they'll run nicely on the ring.N.B. you really want to avoid lumps of solder or other surface irregularities on the slip rings. Soldermask between the ring itself and the pad for the wire is a good idea so you dont get unwanted solder flow. Similarly, on a double-sided PCB the stitching vias should be right at the edge where the brush doesn't run over them. If the rings get excessively worn, you should be able to flip a double sided PCB over if you carefully clean where the wires were attached with solder wick and burnish any remaining rough spots.

author: mribble
author_rank: Regular Contributor
timestamp: March 22, 2018, 07:53:35 pm
content: The DIY solution for the globe in interesting, but I don't totally understand it. There must be an insulator on the inside of the bearing and the metal shaft acts as ground, right? That wouldn't work for me because trying to run a wire and insulator through a larger bearing like that would add vibrations. I could see this working if I could do it with a single wire, but I need 2 wires (power and ground). I'm sure if I manufactured a complex spindle I could get this working, but I can't afford that. If there is a clever diy like solution I'm missing it and would like to hear it.tpowell, the coil idea is an interesting one. I might try something like it, but I don't have a good feel for coil or magnet. I could certainly experiment with it. I do think I need a circuit board though because I need to reverse the direction of the hook when it reaches the end (planned use some tiny micro and detect increased current in motor to decide a direction switch. Maybe I'll do it with all analog parts plus a flipflop since it's very simple logic. I just have to figure out if I can generate around enough current with this method...Ian.M - Thanks for explaining this this slip ring solution. I could see something like that working. This is a second solution to look into and I might have some questions about selecting parts if I go down this path.Thanks so much everyone. If you guys have more ideas keep them coming!

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 22, 2018, 08:01:36 pm
content: Quote from: mribble on March 22, 2018, 07:53:35 pmSolution #2:Place a flat ring on the flat surface on each end of the large wheel, make a springy metal contact to contact it from the stationary pedestal, run power from a stationary power source, whether it is a battery or a PSU to connect to the springy contact. Run a wire (+ on one end, - on the other) from the rings to your circuit/motor. The flat rings will need to be fairly accurately in the center of the wheel in order to maintain contact with the springy, stationary contact points. This should work, just not as fun as playing with the coils and magnets...EDIT: Changed 'middle' to 'center' for better clarity of my thought.

author: Brak
author_rank: Contributor
timestamp: March 23, 2018, 05:14:22 am
content: I see an 8x8 centimeter solar panel on eBay that says it'll deliver 100 milliamps at 5 volts. I assume in direct sunlight.I have no idea how bright a spotlight you'd need to provide the power you need.

author: Ian.M
author_rank: Super Contributor
timestamp: March 23, 2018, 07:14:01 am
content: So I've dug into the related videos and found:It shows the construction (of an older model) in more detail, and why any solution that requires wiring to or inside the shaft (axle), or access to more than one face of the rotating assembly isn't really viable.Moving the yarn hook to and fro over the width of the bobbin is going to be a real PITA even assuming you can get power to the flier. It may be worth considering a mechanical system with a solonoid on the frame that extends a pad that drives a small rubber tyred wheel connected to a threaded rod to move the yarn hook. A second wheel geared to the first (but offset axially) and another pad and solenoid could provide reverse hook movement. Detecting the hook is at its limits to reverse it could be done with a small magnet on the hook and a hall sensor at either limit on the frame.

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 23, 2018, 08:41:35 am
content: Quote from: Ian.M on March 23, 2018, 07:14:01 amits possible (see assy2 in attached mechCAD)Quote from: Ian.M on March 23, 2018, 07:14:01 amsince using proper CAD will take significant time, so i just sketch in mechCAD i supposeit should worth a thousand word. connection between G1/G2 to the motor gearing can be done using platenary gear system with proper gear ratio it can be made... M1 off = hook maintain X position, M1 CW, hook move +X (or -X) , M1 CCW hook moves -X (or +X). but if i have to draw that in mechCAD it will be messed up like hell, so i just leave it here...also known ashttps://en.wikipedia.org/wiki/Epicyclic_gearingwith the interesting math there.need i have to say? that all this will increase the OSHW wooden made machine cost significantly? cheers.edit: gimbal is a wrong F'up term there, it should be counter balance weight, fwiw...

author: station240
author_rank: Unknown
timestamp: March 23, 2018, 09:01:56 am
content: You could try a rotary transformer, which is how VCR's coupled signals from the spinning head mechanism.At a basic level it's just two coils clued to two surfaces, which are close enough for magnetic coupling.

author: Ian.M
author_rank: Super Contributor
timestamp: March 23, 2018, 09:34:05 am
content: Yes, it can be done with a planetary gear box to provide differential rotation of two output shafts, but then you need two toothed belts to the flier (toothed because you can no longer tolerate belt slip) and a second pulley on the flier to drive the yarn hook movement. In addition to the costs of all the precision mechanical parts its going to require a frame redesign and maybe a complete new flier as well.My alternative could be retrofitted to the existing frame and flier using mostly off-the-shelf Meccano parts - the only custom part being the threaded hook drive shaft with its ends turned down to 4mm to fit Meccano gears. On the flier, two small pulleys with fat O rings as tyres, geared to each other by equal sized gears just large enough for the pulley shafts to clear each other, one set on a stub shaft the other on the threaded shaft, possibly with a friction brake. On the frame, two solenoids raising tapered rubber pads to 'kick' one or the other tyred wheel as it flies past, two hall sensors for the hook limit switches and another pair of sensor for flier rotation (one pulse per turn, with direction) or possibly simply tie into the speed control so the hook controller knows which pad to raise (according to flier rotation direction and desired direction of hook travel), how long to hold the pad up and how often to do so to get the desired hook traverse rate.

author: ebastler
author_rank: Super Contributor
timestamp: March 23, 2018, 10:14:38 am
content: It's been done... The "WooLee Winder" uses a purely mechanical, planetary gear solution. They even patented it in 1982. (The patent has expired a long time ago, and of course would not get in the way of rolling your own for your own use anyway). Available as an upgrade for many spinning wheels, but not cheap at well above $200.http://www.wooleewinderstore.com/http://www.thewooleewinder.com/EDIT: For a more detailed description of the mechanism, see the patent, US 4,458,474:https://patents.google.com/patent/US4458474A/

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 23, 2018, 11:06:19 am
content: Quote from: ebastler on March 23, 2018, 10:14:38 amfrom the drawing i got an idea probably a new patent... instead of hook is moving, it will be fixed. bobbin will be moving, so we only need central threaded shaft with some lock pin and bearing. the bobbin movement can be massive, considering its yarn so it should not be so heavy. but saving alot of mechanical components complexity... ymmv.

author: kosine
author_rank: Regular Contributor
timestamp: March 23, 2018, 12:26:09 pm
content: Try espacenet.com. In my opinion it's a much better patent search engine. Google lets you search the body text which espacenet currently doesn't, but espacenet is fully integrated and much easier for patent research. (Original PDFs of the patent can also be downloaded for free.)https://worldwide.espacenet.com/publicationDetails/biblio?CC=US&NR=4458474A&KC=A&FT=D&ND=3&date=19840710&DB=EPODOC&locale=en_EP#If you check the cited and citing documents you'll find another 10 patents from which to borrow ideas. (And many of those will cite additional documents as well.) You can also browse through the classification system to find more, and for European patents it'll even show you the legal history, who currenty owns it, and whether the renewals have been paid.A search for "commutator" brings up about 10,000 hits, which might keep you busy!

author: Ian.M
author_rank: Super Contributor
timestamp: March 23, 2018, 12:32:16 pm
content: Why would you bother reinventing the patent US 4458474A to work around its claims? Its long expired so you can simply use it as-is.Although it is preferable to manually moving yarn hooks, and a threaded shaft in a slotted tube is probably the best way to implement the hook motion, it has a few disadvantages:* it applies a varying torque to the bobbin, depending on the direction of hook travel, with or against the yarn tension so it will cause the rate of takeup to fluctuate and may make it more difficult to adjust the drag.* It is mechanically complex, requiring a custom self-reversing double threaded drive shaft and special nut. Although a similar arrangement is used in some thermal till-roll printer mechanisms, I doubt you'd be able to find a shaft and matching nut that are robust enough and give enough travel.* It needs custom bobbins - their width must match the hook travel, and as originally implemented they must have a gear to engage with the mechanism mounted on the flier, though that could be worked around if the gear ran on a bearing on the spindle with a pin to engage a slot or hole in the bobbin cheek.* Its impossible to vary the ratio of distance travelled to bobbin turns without changing the gear train.A modern solution would use simpler mechanicals, (that can be reproduced without a full machine shop), smarter sensors, actuators and a MCU to do the same job with more flexibility and control,.

author: mribble
author_rank: Regular Contributor
timestamp: March 23, 2018, 12:52:19 pm
content: Quote from: Ian.M on March 23, 2018, 07:14:01 amThis is an interesting idea. I don't quite understand how the 2 different pads and wheels are configured to reverse direction. There is something called an auto reversing thread, which would solve the reversing direction problem (). If my understanding is correct with this specialized threaded rod I could totally get rid your solinoids and just have the wheel always hit the felt/rubber pad when it rotates around. That said it's a little tricky to manufacture this auto-reversing thread and I'm not sure how durable it would be if made out of plastic like I'd want to do. I'd avoid those threads if I can, but I'm also not ruling out such a custom part.My concern with this solution is noise. I would't want there to be a tapping sound, but if I used a wheel and maybe a felt pad it might be ok. I wish I could understand your reversing proposal since I don't understand how that's supposed to work.FYI - This video explains an early prototype of how I'm planning to move the hooks if I keep the motor on the spinning wheel (flyer). I've iterated on this system since then and have a pretty decent solution, but if I could move the whole rotation system off the flyer that would be great.Mechatrommer, I'm having trouble following your proposal, but in a nutshell I think it is this. Use a planetary gear system to rotate the flyer and then tap off the sun gear to rotate a shaft to turn the hooks, right? I'd still need the auto reverse thread system I linked earlier. While this is interesting, I think such a solution would be much to expensive to manufacture for this project. Still I'd like to understand it if it's something other than what I said.ebastler, there are several disadvantages to that design. The biggest is they are using the speed difference in the bobbin and the flyer. This adds tension to the yarn which means you can't spin thin yarn with it since the extra tension won't work with thin yarn. Also that product is expensive as you pointed out and even more expensive than the flyer are the bobbins which need special gearing. The patent was filed in 1982 so it has expired, but I'm sure I can come up with a better new solution.

author: mribble
author_rank: Regular Contributor
timestamp: March 23, 2018, 01:24:03 pm
content: Quote from: Mechatrommer on March 23, 2018, 11:06:19 amI've thought about that really hard and just can't up up with a solution like that and I can't (though maybe something exists, but I'm starting to doubt it). The problem is you need both the bobbin and flyer/hooks to rotate to make yarn. The flyer must rotate faster as that gives the yarn it's twist. Then the bobbin rotates slower to wind the twisted yarn onto the bobbin. Pretty much every spinning wheel uses this design, which means nobody seems to have come up with a better solution (and I think yours would be better if it worked). Even industrial solutions use this same solution, but they move the bobbin back and forth on the shaft, which would take za lot of extra space in my design making it non-optimal. Check out this video at around 3:00 -Ian.M - You summed up the disadvantages of that solution very well. I wish I could understand how your previous proposal was supposed to work. Is it just a couple of gears that let one of the rollers reverse direction?I'm planning to do a Kickstarter with this being an optional accessory so I'm ok with some custom parts because I'd expect volumes in the 100s. I have experience with using factories to make 100s to 1000s of parts in both plastic and metal, but I'd probably want to keep these parts plastic if possible to keep the weight down, but a small #8 threaded aluminum rod is light enough to be ok (that's what my current prototypes use along with a simple micro to handle reversing directions).Another option I've come up with is using something like 4x CR2032 coin batteries. These I could fit on a pcb and would be easy to balance around the shaft. Even if I could only get 150 mA from each one (rated at 220), that would give me 600 mA across all of them which given my low duty cycle should last around 200 hours. Considering even on Amazon you can get name brand Sony CR2032 batteries for $0.40 each shipped that makes the per hour running cost very low (and you can get these batteries in bulk with of brand for about $0.05 each). This would let me use my existing motor on the flyer design, but I'm still interested in spending a few more days thinking about other options before picking one to try and prototype.

author: Ian.M
author_rank: Super Contributor
timestamp: March 23, 2018, 01:46:32 pm
content: Its fairly obvious that one rubber tyred wheel directly on an ordinary threaded shaft, striking a fixed pad on the frame can only drive the hook one way for a single direction of spindle rotation.If you use a pair of gears to drive the threaded shaft from the tyred wheel, the hook's direction of movement is reversed.I therefore propose two tyred wheels, with one directly on the shaft and the other on a stub shaft offset around the flier end plate rim at the same radius. One is nearer the front of the machine than the other so they can be actuated individually by raising ONE of the two separate striker pads their tires will hit.The primary disadvantage of the self-reversing screw is its travel is fixed - if you want to use a different bobbin size, you'd need to change the screw. My proposal (and your simple gearmotor drive idea) reverses when the hook reaches a sensor, which can easily be moved to accommodate different bobbin widths, though hard limit stop collars on the threaded shaft, padded with rubber washers + a friction clutch or other torque limiting mechanism in the drive to the screw would be advisable to prevent damage if a sensor fails or is misaligned.I'm actually not that convinced that a battery solution is impractical. The battery cell(s) can be positioned to mostly counterbalance the travelling hook drive mechanism and motor, though a dummy rod opposite the screw and slit sleeve, and probably a radially adjustable trim weight will be needed for dynamic balance. If the battery can only be removed by sliding it towards the center, which can only be done with the flier off the spindle, there is virtually no risk of the battery breaking away and being thrown off the flier end plate. As the battery will experience nearly 200 G at full speed, I'd try an Alkaline AA cell, mounted positive terminal out so the centrifugal force pushes the contents towards the blind end of the can, not towards the base seal. I wouldn't use a rechargable - putting a LiPO or NiMH under 200G acceleration isn't a good idea due to the risk of internal short-circuit.

author: Ian.M
author_rank: Super Contributor
timestamp: March 23, 2018, 02:38:41 pm
content: Thinking about it further, copper pipe slip rings at the spindle bearings are possible. The front one would run its wire outside the spindle at 90 deg to the yarn hole, and the rear one could run its wire inside the spindle as that portion up to the flier end plate is clear of the yarn. Carbon motor brushes premounted in sprung brush holders are readily available, with spade terminals like your new spindle motor.. The slip rings would simply connect direct to your yarn hook motor. Put all the control electronics in the base and a tiny rare earth magnet on the travelling yarn hook to trigger the sensors. The limit sensors could be moved along a slot from front to back in the base to let the user easily set the limits.Put another magnet on the bobbin at the rear, with a sensor on the frame, and the same for the flier at the front so your controller can make the traveller movement roughly proportional to the rate turns are being taken up on the bobbin.However moving the bobbin, with a fixed yarn hook on the flier is probably much simpler to implement and would certainly have the benefit of keeping all rotating parts light and easy to balance. All it needs is a longer spindle, (or a narrower bobbin) so the bobbin is free to slide along it for a distance equal to its inside width and a threaded rod inside the base driving a slider carrying two rubber tyred wheels with one of the bobbin cheeks running in the slot between them to shift the bobbin along the spindle. Put the bobbin drag mechanism on the slider. Sensors could be simple microswitches, hall sensors or photo-interrupters directly actuated by the slider, bobbin cheek and flier end plate. I'd still want rotation sensors, one sensing the flier end plate, another sensing one of the bobbin cheeks and the final one on the drive to the slider screw so you can keep the bobbin travel proportionate to the rate its taking up turns.Consider using a RC servo to vary the drag tension so the controller can auto-adjust the drag to increase it as the bobbin fills.Is it worth adding a potentiometer or pressure sensor for main motor speed in the foot control for better control when starting or stopping?

author: paulca
author_rank: Super Contributor
timestamp: March 23, 2018, 03:17:59 pm
content: Check some of the RC Heli forums, people run LEDs on the blades at 3000rpm and use power coupling through the swash plate of the rotor head linkage. Might give you some ideas or even parts you can buy and repurpose.

author: mribble
author_rank: Regular Contributor
timestamp: March 23, 2018, 04:08:54 pm
content: Thanks Ian! Very insightful ideas.Here are my top solutions to think about more at this point:1) Battery solution. I like this because I understand best how to implement it and can see if it solves my problem well enough.2) Copper slip rings. I'm a little worried about my flyer moving too much. Having a slip ring on each side of the flyer plate would help with this, but then I need to have a way to move the arms when I want to remove the flyer.3) Moving the bobbin. If I increase the bobbin diameter a little and not loose capacity. Not having sliding hooks sure sounds nice. However, I would need to come up with with a mechanism to move the bobbin like you described.Your servo to control tension is a reasonable idea that I have thought about before. I think a better solution though is to just have a second motor that spins the bobbin. This gives really good control as you can adjust the twist ratio directly. The issue here is to really control the twist ratio you need to know the diameter of the bobbin. Which means I need to know how full the bobbin is and that's kind of hard. I'd need to make some kind of tray to hold the motor if I wanted to go the 2 motor method and move the bobbin (#3).I don't think a potentiometer in the foot switch is worth it. Users sometimes ask for it, but most users find out that having it go back to the speed they were spinning at is really want they want. If I found a cheap pedal with the potentiometer that felt good like the current pedal for the same cost I'd probably switch and make a software option to run it that way. But it's a pretty low priority because most people don't want it to work that way. They just want to tap the foot switch to start/stop it. I can already do a soft start to give people a little time to get used to the speed when they turn it on with the pedal.