Fiber-spinning robot

Help & Support Robot Parts
1

I’m building an electric spinning wheel in which I am considering the use of robotic technologies. One of the troubles is that I don’t know much about robotic technologies. Another is about DC motors; the practical aspects regarding the relationship between RPM & torque ratings, how to interpret & utilize no load RPM & torque ratings, and how to choose a motor. It’s that last question that initially brought me here.

I have some images of a working prototype here. The electrical components I’m using are:

]AC Adapter: 12 V DC 5A output (x5)./:m]
]Controller: 10V 12V 24V 30V DC 3A (x3) & 6V 12V 24V DC 6A (x2). These work well, but I have nothing to compare them to. I like that there are pig-tails for the for/off/rev switch, pot, & DC power jack which allow me to configure their placement in the unit./:m]
]Motor: Mabuchi #RS-555PH. 12Vdc (9-20V) motor. Apx 4500RPM @ 12Vdc, 0.15A (no load rating), torque unknown (x5). Need more speed. Initially fairly quiet, but become increasingly noisy after some 50 or so hours of operation./:m]
The figures in parenthesis are the quantity of that unit that I own. As you can see, I’m not deeply invested in any of those components, but I would like to use them for as long as it seems practical. I’m developing several prototypes at once, each taking their own design directions. These motors & controllers can run for many hours straight, and not get especially hot. The bobbin when fully loaded with yarn weighs 1.4 kg.

As mentioned, I would like to better understand the relationship between rated RPM & torque. For example, let’s say the Mabuchi motor which is rated at 4500 RPM is also rated at 50 g-cm. In fact, I haven’t found it’s torque rating yet. Could a motor with a comparable RPM rating, but 75 g-cm potentially spin the flyer (the parts of a spinning wheel that rotate are collectively known as a flyer) faster? Then, there’s the brushed / brushless question. In tandem with that, I am finding it difficult to learn about brushless controllers. I can’t even yet answer why a brushless motor requires a different sort of controller than the one I’m currently using.

To the question of finding a motor that’s long-lived, very quiet, and < US$ 50, what sorts of RPM & torque ratings should I look for? What other attributes might there be with which I should also be concerned? Do you carry motors with which I might want to experiment, and/or can you recommend something that would meet my needs?

Consider this & the following paragraphs to be of secondary importance to my more immediate questions above. The flyer includes two arms. The job of one is to wrap the yarn around the bobbin shaft, and to evenly distribute it while the job of the other to balance the weight of the first. Traditionally, hooks (such as cup hooks) installed along the length of the arm(s) at 2 to 3 cm intervals are used to distribute the yarn on the bobbin. The spinner must stop the wheel, and manually move the yarn to the next hook. Collectively, those stops & restarts can significantly slow production especially when the speed & direction are controlled by manual foot pedals.

In the last decade or two, a modification has replaced the static hooks with what are known as sliding hooks. There are many designs for these. I’ve decided for now on a slightly modified s-hook, with an o-ring on either side. One side of the s-hook is made larger & rounder to fit loosely around the dowel while the other is closed, and directs the yarn as desired; the slightly undersized o-rings go on the dowel on either side of the s-hook to prevent any unwanted lateral movement. An older spring-like design is still in the images at the above URL. The sliding hooks allow for more even distribution than do the static ones which in turn allows a bit more yarn to be spun or plied before changing bobbins, or emptying the one just filled. They still require that the spinner stop the wheel, and manually move the sliding hook.

A third design, manufactured exclusively by one company so far, utilizes a system of gears, and a self-reversing screw (such as is used in winches, garden hose reels, many fishing reels, and which has the diamond shaped grooves that can be observed in a Yankee screwdriver). A pawl travels in one direction in the first spiraling groove until it reaches the end where it changes directions, travels in the other groove until it reaches the other end and so on. The self-reversing screw shaft does not change direction of rotation. It’s job is to convert rotational motion into auto-reversing linear motion. I am not aware of any manufacturer of these screws that makes stock sizes, and the production of just 1 prototype is, at @ US $2,000 for an import & upwards of $5,000 for one made in the US, or Europe, cost prohibitive for me at this point.

I’m considering another idea which is to use a micro motor placed inside a tube to replace one of the wooden dowels in the current design. It would be wired to it’s controller through an electrical slip ring, a device that allows electrical contact to be maintained when the powered device is rotating around the power source. In turn, it would slowly turn an Acme screw (commonly used in many CNC routers, laser cutters, and the like) which would move something like a screw eye along a slit that runs for most of the length the tube. When the nut that supports the eye reaches either end of the slit, it would activate a micro switch that would reverse rotational direction of the motor & Acme screw.

The significant advantage to this method is that Acme screws can be cut to length from commonly available stock making this a very affordable solution. I’m picturing a single controller that utilizes an Arduino UNO + shield(s?) + programming to operate both motors. This arm, together with it’s internal parts, would be weighed, and a similar tube containing dead weight be installed on the other side, again for balance.

I am not aware of a device that functions like this. Do you see any potential issues with the design? Are there robotic solutions that might solve the rotational-motion-to-linear-motion-in-a-small-diameter-tube design problem more elegantly? I think the biggest concern to me with my idea involves the electrical slip ring. While that may be attributed to my inexperience with them, questions of friction, wear, and possible failure are inescapable to me.

Thanks for having taken the time to read this, as well as for any feedback you might want to provide.

Dave [size=5]:peace_symbol:[/size]

2

Interesting. I hadn’t read about duty cycle before. The AC direction isn’t one to which I’d given much consideration, and I think I’ll go do that right now. I appreciate your time.

Peace,

Dave

3

I looked at your Tamiya RB-Tam-04. The choice of gear ratios over such a wide range, and the mounting brackets make it very interesting to me. Will the AC adapter & controllers I currently have drive this?

I’m not finding many small AC motors, even second hand motors, that are in my target price range (up to $50 for the moment), especially not when their drivers are factored. The ones I do find are slower than I think I want, and probably provide more torque. Also, for the time being at least, I’d like to continue to use the controllers already in my possession until there’s good reason to replace them. For one thing, the power jack, for/off/rev switch, and pot are nicely fit into the hardwood sides of my prototypes as is illustrated in the images that can be found here. For another, I have only a small amount budgeted each month to experiment, try other ideas, or change directions. However, frequent changes of direction doesn’t seem too practical when the expense of electrical/electronic parts, the time it takes to evaluate a change, and the ability to learn from what I already own are factored.

I spent a couple of hours trying to find help to devise a way to measure torque, but I know no more now than I did when I started trying. If T = D x F, what do I measure on my apparatus to satisfy the distance operand? Is D = to the radius of the bobbin? F is the force of what specifically & how do I measure it? Is force in this case related to the mechanical resistance inherent in my mechanism that prevents a motor from attaining it’s full rated RPM?

For example, I could attach a meter, or gauge of some sort to a piece of yarn that’s wound around the bobbin shaft to learn how much force is required to

]cause the machine to move from it’s state of rest into motion/:m]
]maintain desired RPM/:m]

Another useful measurement would also need to be made of that same required force when the bobbin is full. As more yarn is wound on the bobbin, bobbin tension must be increased. Tension is a mechanical resistance, I believe; it acts like a brake, and it’s responsible for the rate at which the yarn is wound. That rate directly affects the tightness of the twist. The higher the tension, the faster & more forcefully the new yarn is pulled onto the bobbin, and I believe the harder the motor must work to keep everything functioning.

This paragraph explains the machines basic mechanics. The flyer is the collection of parts of a spinning wheel that rotate, twist the yarn, and reel it on the bobbin. It consists of a pulley, two arms, a central shaft, and the bar that connects them all. The bobbin’s hollow shaft slides over the flyer shaft which is held in it’s desired position by ball bearings at either end of the belt driven machine. The bobbin spins freely around the flyer shaft until tension is applied with a cord around the bobbin end groove, spring, and knob. When tension is applied, the flyer begins to wrap the new yarn onto the bobbin because it slightly slows the RPM of the bobbin as compared to the flyer. As tension is increased, the RPM difference between flyer & bobbin also increases, yarn is wrapped more quickly, is pulled with increasing force from the spinner’s hands, and a yarn with less twist is produced.

From this description, and with these images, where do I measure D, and what tool do I use to measure F?

I measured current RPM of the bobbin at 460 by threading two contrasting colored pieces of yarn to it in the typical way, and took the balls of those two yarns to the other end of the room. Using a stopwatch, I turned the pot to it’s highest position, waited for 60 seconds, then turned off the machine. By measuring the distance between the spinner & the source yarn balls (total length of the newly twisted yarn), counting the twists in a segment of that length, and doing a little simple math, I calculated 460 RPM.

It gets wonky for me at the next stage, however, because math is embarrassing difficulty for me. The pulley at the motor has a diameter of 1/2". The diameters of the compound pulley are 3", 3.5", and 4". Does this arrangement give me ratios of 6:1, 7:1, and 8:1 respectively? If I use the 4" sheave, and the bobbin attains 460 RPM, then is the RPM of the motor pulley 8 x 460 = 3680? If so, can I calculate that using the 3" sheave will rotate the bIobbin 3680 ÷ 8 x 6 = 345 times per minute…or is my thinking backwards? Once my formula is correct, can I draw any conclusions about torque? If that 460 RPM figure is accurate for my current top speed, then I’d want a motor that would spin the flyer at something closer to 1000 or 1200 RPM. While this is probably faster than most spinners need, or even manage, it will allow the spinner to develop his/her skills rather than limit them. This is intended to be a piece of production equipment, and will get moderate to heavy daily use. High operation speed, component longevity, and quiet are all-important.

Does this help? Does the Tamiya still seem like a good next step? Can I use my current controller with an adapter in the 3 to 6 volt range to drive it?

Peace,

Dave

4

I didn’t type the correct specs in my OP for one of the controllers. I’ve made the correction to read 6V 12V 24V 6A.

The whole duty cycle thing has me stalled. The motor that’s seen the most use has probably operated for 200 hours over the course of the last 9 months. Recently, it has operated for a fair number of moderately long sessions of 2-3 hours of continuous use, occasionally more . It has become considerably noisier, but I don’t believe the speed has suffered. I have not seen many continuous duty motors.

I began my motor search by looking at sewing machine motors which are universal motors; it seems they don’t reverse without modification which often voids warranties.

I am increasingly interested in your Tamiya Planetary Gear Motor. I see in it’s description that it uses a Mabuchi motor. I don’t see anything in the description, though, that suggests that it is continuous duty, so I’ll ask if it is?

It occurred to me that a cooler for computer components might be modified to keep the motor cool, as well as the chips with heat sinks on the controller, but then I read, “The Hitec Robotics Continuous Rotation Servo is a standard servo modified for continuous rotation.” I imagine you’re talking about a mod at the armature level? What about a fan to pull air through a motor?

I guess I’m trying to figure how to beat the duty cycle into submission, or to render it irrelevant altogether so I can justify the purchase of a couple of those Tamayas for use in this little machine.

The bobbin is nearly full. When it is, I’ll attempt to see how much weight is required to set the static bobbin to motion. That won’t be hard at all. I can use a little plastic bag with pennies tied to the bobbin yarn, under the tension required to reel the yarn at that point. What I can’t figure is what to use to measure maintenance torque. Wonder how I could make something that I could splice in-line that uses a spring to move an indicator of some kind.

Peace,

Dave

5

Wow the robot looks cool and I want to know more about[size=2] [highlight=#ffffff][font=Arial, Helvetica, sans-serif]Wrap Reel machine. I will be happy if you can reply.[/font][/highlight][/size]

6

Question is, what torque and RPM do you need? You can vary the RPM and direction of a motor using a motor controller, but you don’t have much control over the torque: a DC motor will consume as much current as it needs to provide a specific torque. Ideally you would operate the motor at a specific voltage which provide a specific torque. However if you change this voltage, the torque changes as well. A motor’s stall torque is when the shaft is locked; which should never be the case; you can assume the maximum continuous torque a motor can provide is around 1/5 to 1/4 the stall value.

Also, DC motors have a duty cycle, meaning they can only operate for so long before they overheat. Most of the time the duty cycle is around 25% (for example 15 minutes on, 45 minutes off). If you plan to connect this to a wall as opposed to a battery pack, you might consider an AC motor instead (we don’t offer any simply because they are not used much in robotics).

7

Try to devise a way to measure the torque. Remember, torque = distance multiplied by force. It depends on the friction in the system and the resistance in the wire. One way might be to purchase a more “universal” motor where you can change the gearing manually, such as the Tamiya Planetary Gear Motor.

8

The Tamiya motor operates best at ~3-6V, while your controller starts at 10V and your power supply operates at 12V, so not the best fit.

For your Mabuchi motor, it’s important to note the duty cycle. Running for 50 hours straight would certainly damage it.

You should choose two positions: one where there is very little thread on the bobbin (so a very short distance) and another where there is a lot of thread. Your idea seems sound; add a meter (or known weights) to see how much force is required. Note that it should not be much.

The harder issue is if you want the traveler to move according to RPM and how full the bobbin is at the time so it’s spooled evenly.

9

No, it’s not really rated for continuous 24/7 use.

Those have no torque at all. Brushless motors can rotate for very long periods and would be worth considering. They require a brushless motor controller or an ESC (not a brushed motor controller).