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RE: Open Source Chemical Analysis [Everyone Welcome]

alfred3axel — Mon, 22 Jan 2018 13:09:44 GMT

I was looking a website that provides all chemicals used in marine industry.

RX Marine was established in 1996 in Mumbai, India; as a chemical manufacturing company catering exclusively to the needs of the marine industry. In a short span of 12 years the company has established itself as one of the leading wholesale suppliers of a wide range of chemicals for - Marine industry internationally - and other local industires and plants. Our client list bears testimony to this. The RXSOL policy has its foundations on two pillars of strength - a continuous investment in research and development to deliver premium quality products and a commitment to service.

Degreaser

Thanks!

Alfrad Axel

Open Source Chemical Analysis [Everyone Welcome]

m.ratcliffe — Sat, 03 Oct 2015 12:36:37 GMT

A lot of us here are working on hydroponics or aquaponics, a lot of the sensors are outdated and it would be great to have more information about the growing fluid at our disposal. On this page it would be great if we could discuss general techniques and potential prototypes to measure all the things we feel are important in a growing fluid.

Aims, to make a cheap [sub $XXX] spectrometer[or other] capable of measuring the quantity of chemicals in a liquid:

>What is needed :

Automated Green House Blog:20.1 - Toying with Chemical Analysis - Essential Nutrients

What is bad and can accumulate:

> [Coming Soon]

>Other things we can think of

Types of sensing [this will grow larger I hope and each one will have its pro's and cons listed]

>IR Spectrometry

>UV Spectrometry

>Mass Spectrometer [Will build this later]

Other ideas:

>Change frequency of AC EC measurments, maybe we can see polarisation happen for each element at a certain frequancy.

>Charge a probe to +5 and measure its depletion curve. maybe there will be peaks at certain times as polarisation is reversed.

I know very little on this topic right now, but maybe with a few of use we can make it work.

Maybe we could share the load between us and each tackle a small portion of the problem each, ie write up a little about what we need to measure, each sum up a common technique used today and pro's/cons of automating it.

If anyone can think of a better place to house this discussion on Element14, please let everyone know. And could one of the admin tag everyone in it, so all of the other great contest content does not put it in their shadow.

Some Useful Links:

http://store.publiclab.org/products/desktop-spectrometry-kit-3-0

Message was edited by: Michael Ratcliffe Anyone can Alter the content, please leave a short summary here of the changes

Contributors:

[mention:effa1c581c6d49849f624f21b6bc626b:e9ed411860ed4f2ba0265705b8793d05]

[mention:cbaee65a7b9e4999b7376a1f5dce129c:e9ed411860ed4f2ba0265705b8793d05]

[mention:b0bc65b9ecdc4307bd967592f00e340a:e9ed411860ed4f2ba0265705b8793d05]

[mention:a5312e9762dd4699ba5d3876da34ffe5:e9ed411860ed4f2ba0265705b8793d05]

DAB I cant find a way to link you, but do you want to join the project?

Mechanical Design Assistance???

RWReynolds — Thu, 06 Aug 2015 02:28:48 GMT

Hey everyone,

I'm not a mechanical engineer by any stretch on anyone's imagination. I have one mechanical design issue that I'm not sure how to approach. I kind of know the theory, but I have no idea how to approach it practically.

Here's the problem...

I have a load, my cultivator unit, that will be about 3' - 4' tall, maybe 12" to 18" in diameter and weigh between 20 and 40 lbs. The whole thing will be mounted on a lazy susan style turntable. The plan is to have a gear or pulley at the bottom that will be used with a hight torque stepper motor, and chain or belt, to rotate the cultivator. I'm using a stepper motor because they are pretty efficient and can be controlled very easily at very slow speeds. I want the rotation speed to be maybe 3 to 4 revolutions per day. A stepper would work well for this I think.

I have no idea how to properly size the motor. I see them speced at anywhere from 10s of oz-in to 1000s of oz-inches of torque. I get the concept of torque being rotational force. And that required torque has to do with acceleration time up to the desired RPM. But I have no idea how to relate this to my requirements.

I'm a 'puter software with some dangerous electronics knowledge guy! HELP!!! And feel free to tell me this just a stupid idea and I should be using a washing machine motor or something if that's the case.

For reference, here's a drawing of the rig. Note the drive at the bottom right. Please excuse the misspelled labeling. I haven't gotten around to correcting it yet. lol...

[View:/resized-image/__size/620x438/__key/communityserver-discussions-components-files/127/4578.contentimage_5F00_59281.jpg:620:438]

RE: Mechanical Design Assistance???

Former Member — Mon, 21 Mar 2016 19:09:13 GMT

Repeating Mark's comment from above (https://www.element14.com/community/message/157611/l/re-mechanical-design-assistance#157611 ) here:

In considering that in connection with multiple stepper motors:

If in fact 4 steppers were used it seems Torque & power of each (approx 2.83Nm / 27 W) may be readily available.

Is there any benefit between having the pivot at point "A" or point "B" on the plate?

Is any particular placement of the spring preferable and how might it's "strength" be calculated/selected?

Should I assume the plate itself should, at least, be Aluminium?

Any comment (other than it will be expensive ) appreciated.

Andrew.

PS: John, I checked out the wheelchair - it seems the motor is probably a Merits Health Products 24V 120Watt. I've been unable to find any details of the controller.

RE: Mechanical Design Assistance???

Former Member — Sun, 20 Mar 2016 18:46:04 GMT

Appreciate your further comments Mark.

Unfortunately the Trinamic youtube video I linked to previously does appear to show the easiest way to do this is by using the equations. It would be similarly straightforward to pre-calculate 500 points if a linear acceleration profile were desired (rather than sin²) - I believe ther Arduino library (Accelstepper) that I previously referred to does this linear acceleration "on the fly".

"Most DC motors would have some form of curve (Torque v speed/rpm) and the shape of that curve would vary."

For the record, here's the Torque/Speed profile for my 1 second move (Set1a) - the original model assumed zero friction (perhaps stiction in angular talk?) and a 14.5 gearhead reduction:

DC Motor problem?

As I now understand it - the big problem with trying to use a dc motor with a pre-calculated time/motor current (via PWM) profile is, of course, that the calculation is only accurate for the single moment of inertia on which the motion model was built. I hadn't recognised the full significance of this in my previous quote, repeated here:

i.e. it was referring to a system with constant mass (or moment of inertia in my case) and therefore no requirement for encoder feedback.

On further contemplation of such a system - while it may be theoretically possible to calculate (and position) a suitable extra mass on the turntable (in addition to the mass of the person to be scanned) to keep the complete system moment of inertia constant each time a scan occurs that seems totally impractical. Final position errors would be inevitable in practice.

Further, at the minute, assuming no attempt were made to maintain a constant moment of inertia, I can't visualise how I could use an encoder with feedback to successfully inter-relate with the single pre-calculated PWM table in order to provide precise position/speed control.

So, while the torque/power characteristics of steppers are far from ideal it does seem possible that the pre-calculated table of stepper step times referred to in my post here https://www.element14.com/community/message/177404/l/re-mechanical-design-assistance#177404 is possible of replicating the required motion profile even if the system moment of inertia should change & open loop. I agree, unfortunately, this is not a straightforward approach and may require multiple steppers to provide the required Torque/Power (by simple arithmetic addition of each) but, at the minute, it actually seems the most straightforward approach.

I'd wish to be proven wrong though.

Andrew.

RE: Mechanical Design Assistance???

mcb1 — Sun, 20 Mar 2016 11:53:55 GMT

niman

Andrew,

While I presume the maths is correct (beyond me I'm afraid) the actual torque is also going to be dictated by the speed.

Most DC motors would have some form of curve (Torque v speed/rpm) and the shape of that curve would vary.

I think you might be overthinking this by trying to plot 500 individual points.

It seems simple to me, decide on the gearing that provides a suitable rotational speed that your subject will be comfortable with.

This will be the speed that is 100% or 255 PWM value.

It might be that the nearest you get is using a PWM value of 230. ie 230 = full-speed

Do some experimenting with the acceleration time to go from something above zero to full-speed to prevent 'jerking the subject'.

The de-acceleration time/rate is likely to be very similar.

You can change the rate of PWM by changing the step value as it likely that changes at the lower end will have more effect than changes at the upper end.

Storing 500 numbers is not a problem as they are all bytes (0-254)

Mark

RE: Mechanical Design Assistance???

Former Member — Sat, 19 Mar 2016 22:29:51 GMT

Hi John,

"The next time you have one of these great questions it would be best to start your own thread."

Understood and will do (I have one about maintaining ptp communication over the usb cable data wires while switching the 5v usb wire (which can act as a trigger to start exposure on multiple cameras with extremely high synchronisation) that has been in the back of my mind for ages that somebody may be able to comment on).

"I saw a person in a motorized wheel chair do a 360 degree pivot"

Cheers - will dig into that.

Thanks,

Andrew.

RE: Mechanical Design Assistance???

Former Member — Sat, 19 Mar 2016 22:22:41 GMT

Hi Mark - apologies for any confusion...I should have mentioned those most recent comments were meant only to relate to a single 30° movement

Returning to 11 movements (and therefore discounting a crank & connecting rod for the moment) - In between watching some sport I read a little of the basics of dc motors today for the first time. In summary my current understanding is:

Torque (and therefore angular acceleration) is directly proportional to Motor Current and
Motor Current is directly proportional to the portion of the 2ms (assuming a 500Hz PWM Freq) period in which that pin is "HI".

If that is accurate then the zero Jerk "60.76sin²(2πt)" Acceleration profile I previously calculated and reported in the diagram here (Set1a): (https://www.element14.com/community/message/177404/l/re-mechanical-design-assistance#177404)

already has figures calculated to apply the correct fractional multiplication to result in the portion for which each (and every) 2ms period remains HI for the entire 1000 ms 30° movement (i.e. the relevant arduino analogWrite(0 -> 255) value for each). The actual acceleration function values were calculated automatically and graphed in a simple Excel spreadsheet). I still have no idea if a ucontroller memory has facility to store an array of 500 values.

So, my guess is that I already have the 250 required +ve Accelerations (i.e. motor +ve Current) values & 250 required -ve Accelerations (i.e. motor -ve Current) values available to enable the proposed motion but since this is currently not an exact science (unlike the stepper open-loop) I believe I now need to understand something of feedback and encoders (or something).

Experimenting? absolutely - the number of times i've measured 3 times and still cut wrong is woeful. It's also possible my understanding of the theory is also off the mark & I just haven't spotted that yet.

Still baby first steps here but thanks again for mentioning the possibility of dc motors which may ultimately be more straightforward (we'll see).

Cheers,

Andrew.

PS: From what I can see it's only the crank model that has any particular mathematical complexity - I don't really want to have to remember what the "j" operator and all those matrices are for (if at all possible) so if a crank & connecting rod forms a part of the solution it will be more by experiment than anything else

RE: Mechanical Design Assistance???

mcb1 — Sat, 19 Mar 2016 20:38:41 GMT

niman

Andrew, regardless of the equations a crank will not give you a full 360 deg rotation of the turntable.

You are correct that the speed will not be linear, and the easist way to draw this is to plot the amount of movement of the pushrod for each degree of rotation at the drive end.

The greatest 'speed' will be when the crank is at a 90 degree angle.

You don't need any fancy software packages in order to work out what is best.

In your software you have a start, PWM starts at a low duty cycle and increases over x time.

For slow down the reverse happens.

It will take a little experiementing and maybe the glass of water is a good 'model'.

Cheers

mark

RE: Mechanical Design Assistance???

jw0752 — Sat, 19 Mar 2016 19:50:57 GMT

Hi Andrew,

The next time you have one of these great questions it would be best to start your own thread. The original author is steadily collecting points for our posts and you might as well be the one in the future that gets the credit.

I saw something today that gave me another idea for your rotational platform so I will throw it out there. I saw a person in a motorized wheel chair do a 360 degree pivot as if the chair was attached to one point on the floor. I don't know if they all can do this but this one could. If you could find an old chair cheap and remove the seat and upper structure you could use the control mechanism and the PWM drive to the motors to create a system platform that would rotate at nearly any speed. You would still have to work out timing or limit switches to get a precise 30 degree rotation.

John

RE: Mechanical Design Assistance???

Former Member — Sat, 19 Mar 2016 12:08:11 GMT

Excellent stuff Mark - you comment just prompted me to read this reply in connection with someone enquiring how to move a cup of liquid back and forth between drink dispensers:

The equations related to John's 4 bar linkage (single degree of freedom) are a bit beyond me at the minute and while certainly not equivalent I can sort of imagine it may not be unreasonable to model that as a piston, connecting rod & crank in which case the displacement, velocity & acceleration equations are fairly straightforward.

Assuming the simplification is relevant then if the crank has instant (from t=0) constant angular velocity then it is only in the case where the radius of the crank is small in comparison to the length of the connecting rod that the motion becomes close to sinusoidal. When the crank is longer we get something like this:

Long crank or short (assuming instant crank constant angular velocity) - acceleration is initially discontinuous and jerk is a theoretical infinite impulse function.

Defining a suitable PWM profile therefore seems necessary (even for the simplified system I describe) but is likely beyond my analysis capability - i'm not sure I want the bother of a "Matlab" license at this stage of life.

Or maybe John's comment (re human is not like a cup of water) hasn't really sunk in yet and I continue to see a problem where none really exists

Plenty of food for thought though (including learning the characteristics of a DC motor in some detail).

Thanks,

Andrew

RE: Mechanical Design Assistance???

mcb1 — Fri, 18 Mar 2016 23:01:24 GMT

With the new information added I think there is another option you could explore.

If you were to use a larger 12v DC Motor driving the turntable, you could simple PWM it to start and then detect each 30 deg point on the turntable and stop the motor.

The detection could be a simple Hall Effect switch with the magnet on the turntable.

You can gear it down as the turntable is what controls it, and I'm thinking that a windscreen wiper motor from a vehicle is small, powerful and inexpensive.

The stepper system is going to require a lot of gearing as they typically don't produce a lot of torque.

A brushed motor allows a variable load to be applied across the motor when it is slowing down, while the stepper is either nothing or full stop.

It sounds like a great idea, and yes getting someone to 'notmove' during this will be the hardest thing.

I'm alos thinkign that the person's referecne point will shift making it difficult (unless it is a round room).

Mark

RE: Mechanical Design Assistance???

Former Member — Fri, 18 Mar 2016 20:14:55 GMT

"...[]...but sometimes even an off base idea will send one in a different thought direction."

Couldn't agree more John - appreciate all you comment above.

"Without knowing all the details of your idea..."

I seem to have been writing an autoit (https://www.autoitscript.com/site/autoit/ ) tcp/ip client/server system to control a host of cameras (based on the Canon compact camera hack called "CHDK") in "fits and starts" for absolutely ages - my system can, theoretically, manage an unlimited number of cameras capturing images with a synchronisation difference of approx 30ms across all units. The images will be fed into a photogrammetry package to create 3d point clouds with ultimate goal being 3d figurine printing - there are a multitude of other possibilities related to the data. Higher image count in minimum time is the ideal combination.

I currently have 48 little cameras but had decided to do preliminary testing with a single vertical "pole" of 8 cameras, a tailor's dummy and a turntable. Each of 11 stops at 30° requires all cameras to autofocus, synchronised shooting, waiting for the image to finish writing to the cameras buffer (not inconsequential when dealing with RAW images) before restarting rotation - 96 images in total.

With my full camera count of 8 cameras on 6 "poles" (and a living subject) a single 30° movement will provide the 96 images (of course 2 x 15° moves gets me 144 images with increased time/movement as tradeoff) - I still have a feeling that "stepwise Jerk" may affect children negatively, even on instruction to "stay still", so will probably investigate the sin² some more.

Perhaps i'll just set my 6 poles up now and think some more about your "alternative" solid link idea

I suppose I could consider multiple of those solid links and multiple smaller steppers to provide required torque/power:

Thanks again for your idea (I loved the sketch!)

Andrew

PS: this is probably the most boring & poor quality video on youtube - it may give an impression of what i'm, fitfully, up to https://www.youtube.com/watch?v=B68XZsCgLYc

RE: Mechanical Design Assistance???

rsc — Fri, 18 Mar 2016 17:44:06 GMT

If you take apart an old microwave oven with a rotating turntable inside, you may find all the parts you need.

Scott

RE: Mechanical Design Assistance???

jw0752 — Fri, 18 Mar 2016 15:54:07 GMT

Hi Andrew,

I don't have the experience to address your uControler question. Reference the mechanical aspect of your project I am assuming that you are still planning on rotating a human through 30 degrees and then back to the original position. I would not worry too much about accelerations in this system. The human is an adaptive system and not like a glass of water. The muscles and joints and their related sensory and reaction systems will absorb and modify the rotation. I would suspect that a rotation of 30 degrees, particularly if it is anticipated, might not even change the visual point of focus of the individual and while the feet will obviously rotate the 30 degrees the rest of the body will likely follow the rotation at a more leisurely pace. Here is an alternate idea for producing a 30 degree back and forth movement in your platform. Without knowing all the details of your idea I may be off base but sometimes even an off base idea will send one in a different thought direction.

John

RE: Mechanical Design Assistance???

Former Member — Fri, 18 Mar 2016 10:33:09 GMT

A quick update.

I don't currently possess the skills to build the Trinamic2461 chip into my solution (it's "on the fly" motion controller does seem to have what i'd like though).

Google doesn't report too much on this but I ran across the fact that the sin² function has a first differential which is continuous as are both it's first and second integrals - so using that as a base acceleration function seems like it will provide a decent motion profile. In my case (using a gearhead ratio of 14.5 and a start-to-stop time of 1 second) the stepper must rotate a total of 435° (7.595 rads) for turntable 30° rotation then the appropriate acceleration function turns out as 60.76sin²(2πt).

241.67 stepper pulses will do the trick (i.e. 242 for me). The complete motion profile is calculated then graphed as:

Since each step (1.8°) adds 0.031428 rads to the distance then solving the distance function for each of the 242 provides each required pulse width (I used a website solver to provide the 2 step integration function).

Unfortunately the related Torque ( τ = 0.1863 x α) & Power (Power = 0.1863 x α x ω) calculations reveal greater figures than, I believe, any current stepper capable of:

That has max τ of approx 11.32Nm and max power of approx 108.33 W

I'll redo the figures based on a +0.75 / -0.75 sec accel/decel profile and hope the Torque/Power look more achievable.

Queries:

I have zero μcontroller experience but would wish to feed the 242 pulsewidths that are calculated above into an array and use something like the Arduino "delayMicroseconds" command to create the pulses (along with "digitalWrite") - is it possible to create an array of that size in a μcontroller (which one)?
I still haven't identified a mechanism to direct couple the gearhead output to the centre of rotation of the plywood so if anyone can usefully comment it'd be really appreciated.

RE: Mechanical Design Assistance???

jw0752 — Wed, 09 Mar 2016 14:18:29 GMT

Hi Andrew,

Thanks for the link. It is quite impressive to see the difference between the steady and contoured acceleration rates. This is a good example of how interesting things can get when we take the time to dig deeper into the physics. I saw your first post as it came through on my e-mail notice but then I couldn't find it on your E-14 posting so I assumed that you edited it off. Thanks for reposting as I am sure others will find it interesting too.

John

RE: Mechanical Design Assistance???

Former Member — Wed, 09 Mar 2016 08:27:52 GMT

Hi John - I see you are still in touch with the thread

I had initially included the following link (in my post above) as an example of what rate of change of acceleration could "look like" wrt the the human body (jelly) but had then deleted it.

In case you missed it i'm sure you'll find the re-instated link interesting https://www.youtube.com/watch?v=X4X_EUxqKEo&feature=relmfu

Andrew.

Edit:

for the record, I currently understand step changes in d/dt(Acceleration) to be referred to as "jerk".

RE: Mechanical Design Assistance???

Former Member — Tue, 08 Mar 2016 08:30:50 GMT

Well, I received my 390mm dia lazy-susan a while back (image attached) but it'll sit in a corner some more yet.

Reading lots that I hadn't been aware of e.g "inertia-matching" it seems direct-coupling of gearhead/stepper to the turntable may be preferable (neither had I been fully aware of the reduction in reflected load inertia by the square of the gearbox ratio).

While a direct coupling scenario does work around some complexity (belt-drive redundancy / no requirement for circular ply) I can't say that the lazy-susan bearing is the most accurate "circle" i've ever come across (the bearing is a little sticky at a point to rotate by hand).

Perhaps the accuracy that would be required via a direct coupling from the gearhead output to the underside of the plywood make this newly conceived contrivance impractical?

If someone where to comment on this point it would be useful. However, if the idea where seen as potentially practical then any hint to the nature (by example) of a gearhead shaft to underside of plywood "coupler" would be appreciated as I have very little idea what that could be.

Andrew.

RE: Mechanical Design Assistance???

Former Member — Sun, 28 Feb 2016 10:14:28 GMT

I'll keep that in mind Mark - at the minute I have one eye on keeping the solution mobile (and weight down) so will try the lazy susan and some roller bearings around the perimeter first.

Understood John - while that will keep torque down i'm equally concerned about the effect (on the person) of the sudden change from +ve accel to -ve accel (not mitigated by the period of zero accel). Of course, the fact the shorter periods of accel/decel must be harsher may offset the benefit I refer to...perhaps a short period of zero accel will help.

We'll see!

Thanks,

Andrew.

RE: Mechanical Design Assistance???

jw0752 — Sun, 28 Feb 2016 06:02:18 GMT

Hi Andrew,

The reason I suggested a steadily accelerating and decelerating program is that for any time frame it will have the lowest dv/dt. Any time spent at constant velocity is a waste and only creates the need for higher torques and higher accelerations at the beginning and ends of the cycle.

John

RE: Mechanical Design Assistance???

mcb1 — Sat, 27 Feb 2016 22:31:05 GMT

As jw0752 said the postion could affect the friction.

As a cheap source you may wish to consider using automotive components.

Either the rear or front hub turned on its side, would easily cater for uneven loading while retaining the same friction.

Depending on what option you choose the drive axle could be retained to allow different options to drive it.

Looks like an exciting project.

Good luck

Mark

RE: Mechanical Design Assistance???

Former Member — Sat, 27 Feb 2016 16:28:28 GMT

Much appreciated John - food for thought. I guess the proof of the pudding is...that it wobbles . Much experimenting & various poses required - neither is the 1.5 secs set in stone.

I had imagined the 100Kg load / position as the over-engineered extreme (I should have mentioned that though).

"15 degrees of acceleration and 15 degrees of deceleration"

I'd prefer something approaching a sinusoid (i.e. zero, slight +ve, large +ve, slight +ve, zero, slight -ve , large -ve, slight -ve, zero) for the acceleration profile but I haven't looked in detail whether that can be approximated by a series of steps through the AccelStepper library yet.

To be honest I have practically zero mechanical design experience and i'm probably hoping for further comment re how to identify a suitable stepper and how to size the pulley and belt pitch gearing relationship...

Thanks,

Andrew.

Edit:

Having reviewed the "trapezoidal velocity profile" produced by the the positive accel pulse / zero accel / negative accel pulse i'm no longer sure the sinusoid accel profile I had referred to would be any better than this:

RE: Mechanical Design Assistance???

jw0752 — Sat, 27 Feb 2016 16:01:13 GMT

Hi Andrew,

Your person standing on the turntable makes any specific calculation of the torques involved very difficult. The structure of the human body will absorb the movement and only follow a 1.5 second rotation in an elastic manner. To smooth out the rotation I would consider 15 degrees of acceleration and 15 degrees of deceleration. This will slightly improve the amount of torque needed and should improve the overall feel of the rotation to the subject. Foot position of the subject on the disk should not affect overall torque but an imbalance of weight distribution may make friction in the bearings a factor that needs to be considered. Foot position may also affect the amount of elasticity in the bones and muscles of the body and hence change the dynamics of the rotation. By over engineering the problem you should be able to make it work.

John

RE: Mechanical Design Assistance???

Former Member — Sat, 27 Feb 2016 13:40:44 GMT

Fist post here. I hope it's ok to continue on an old thread - there are some similarities to my current project.

It's a long time since I attempted any angular motion calculations - so please forgive any obvious mistakes...I have ignored friction below on the assumption it will be negligible compared to torque/power required for acceleration (not sure if that is wise though).

I'd like to use a stepper (or steppers if needed) to rotate a plywood disk (with a person standing on top) of 1200 mm dia 30° in 1.25 secs. The timing belt drive disk will be 1160 mm dia as the centre of a 1200/1160/1200 mm sandwich with a lazy susan on the bottom. I plan to use something like the AccelStepper library (not sure if providing a link to that is ok?) to do:

from rest provide constant acceleration for 0.5 secs
constant angular velocity for 0.25 secs
const decelerate for 0.5 secs to rest

I calculated the approximate moment of inertia (plywood + person as 100 kg point load on perimeter of disc) as 39.16kgm²

Torque/Power Calculation:

Say, use Accelstepper Library to apply the above:

(i) constant acceleration, α, (from 0 rad/s) for 10° to maximum ω rad/s. Say time taken = 0.5 secs

(ii) zero acceleration for 10° to 20°. Say time taken = 0.25 secs

(iii) constant deceleration , α, from 20° to 30° for 10° (from ω rad/s to 0 rad/s). Say time taken = 0.5 secs

i.e. total time taken is 1.25 secs for 30° start-to-stop

Considering only item (i) for now:

Angular Displacement, θ = 10° (or 0.1746 rads)

For rotational motion with constant Angular Acceleration:

θ = (1/2)(ω₀ + ω)t

since ω₀ = 0 rad/s

0.1746 = 0.5 (0 + ω) 0.5 -> ω = 0.1746 / 0.25 -> ω = 0.6984 rad/s

α = (ω - ω₀)/t -> α = (0.6984 - 0)/0.5 -> α = 1.3968 rad.sec^-2

Torque required to produce this stated radial acceleration:

τ = Iα -> τ = 39.16 x 1.3968 Nm -> τ = 54.7 Nm (Max)

Force required to produce this Torque:

τ = Fd so F = τ / d

"d" for the disk with the glued on timing belt is = 1160mm/2 = 0.58m

therefore

F = τ / d -> F = 54.7 / 0.58 -> F = 94.31 N

Work done by torque τ is W = τ x θ

Power, P = d/dt(W) = d/dt( τ x θ ) = τ x dθ/dt

since ω = dθ/dt

Power = τ x ω

Power = 54.7 x 0.6984 -> Power = 38.2 Watts (Max)

Question(s):

I have a rough idea how a stepper works but i'm not really sure how to specify a particular stepper/gearing ratio to "make this happen" - any ideas along that route would be most appreciated (based on quoted power alone I have a feeling I may need 2 x Nema 42!!).

Other:

of related interest - using an 80MHz processor (compared to a 16MHz Arduino Uno) increases the Accelstepper acceleration 5 fold e.g. https://www.youtube.com/watch?v=Hsl3dbRPLTw

...that e.g. used a bipolar nema 34 at 1.8°/step (200steps/rev)