Design and build a spin coater-----make money online

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today on applied science of going to

talk about how I designed and built this

spin coater so I'll describe everything

I learned about low-cost motor

controllers and make all the code and

circuitry available in case you have a

similar motor based project so let's see

this thing in action it's got a rotor

here and I've put Flathead brass screws

in here so that when I slip a microscope

slide in and put one more screw in it

holds it down and keeps it from moving

on the rotor so I press the green button

and it spins at about 400 rpm

indefinitely and the idea is that you

want to put a liquid on to the spinning

slide and the spinning motion of the

spin coater will fling the liquid out

and make a very even coating on the

slide so I'm going to use this liquid

which is a photoresist and I realize I'm

doing this under shop lighting so it's

not going to be really useful but this

will just give you the idea and then we

press the green button again and the

Machine goes through a very controlled

acceleration up to about 3000 rpm

and when it reaches 3,000 it holds the

speed and it's counting up in seconds so

the whole idea here is that we want this

process to be very repeatable because we

want a very consistent even layer of

photoresist I had a different spin

coater previously that didn't work

nearly as well so this is a really nice

upgrade you'll see we're getting up to

about 30 seconds 32 the machine has a

really rapid deceleration and then you

can see that the slide is now nice and

coated with this green photoresist so

here's a slide I coded earlier you can

see that after it sits out under the

fluorescent lighting this one is nice

and green this one is nice and blue

because it's been exposed by the

fluorescent lighting in the shop so

let's take this thing apart and you can

see how it's built this splash guard

just lifts out it's actually just

sitting in here captain side-to-side

with these plastic blocks here but it

really just lifts out and the reason it

has this internal lip here is so that

when the thing flings excess liquid out

it will fall down into this moat instead

of making a mess on the table so as you

can see here this is using a motor

designed for like a quadcopter or

something like that and the reason for

that is that the market for these motor

controllers and motors for quad copters

is really developed so you can get these

for very cheap so I bought a couple just

because I mean this is like fifteen or

ten dollars or something like that and

the controller for it is similarly about

ten or fifteen bucks it's so cheap that

even single chips from digi-key that

would do a similar thing cost almost as

much as the entire board so let's open

this up and we can see what's in here

okay so here's the insides of the box

and this project was definitely a case

of using whatever I had available on the

shelf so a lot of these things I already

had in fact the only thing that I

actually bought for this project was the

motor in the controller itself but

anyway let's take a look at this so

we've got switched mains coming in here

coming down to the switch mode power

supply

it's about seven and a half or eight

volts kind of weird but that's actually

the voltage that I needed and I just

happen to have this playing around then

we have an old-fashioned parallel

interface LCD up here the motor

controller and an Arduino micro that

runs the whole show so those two buttons

are disconnected right up to the Arduino

micro and we're using its internal

pull-up resistors to sense the state of

those buttons a nice little tip if

you're using a abs project box like this

and you want to mount a circuit board or

a heavy thing like this what you can do

is cut some chunks of thick ABS plastic

this is maybe 3/8 of an inch thick and

drill a hole and tap it in this chunk

and then what you can do is attach the

chunk with a screw to your circuit board

kind of like that thread that in there

so that there's a plastic foot here and

then just drop the whole thing in to

your plastic enclosure and then add some

solvent weld I ran out of thickened a

solvent weld that you can use this on

abs you can also just use sewer pipe

cement from the hardware store it works

great very strong like that foot the

project box itself will break before

that foot comes off so if you need to

fix something like a heavy power supply

board this works just fine it also gives

you the ability to kind of move it

around inside the project box before you

commit to it okay so let's talk about

motor selection for a second when I

started this project I didn't know that

I was going to be using one of these

quadcopter motors I thought oh you know

maybe a stepper motor would be okay and

this project is not particularly well

suited for a stepper motor because the

speeds are kind of high so you saw it

was running at 3000 rpm but potentially

we'd want it to go up to four or even

5,000 rpm and that's really pushing it

for a stepper motor in addition the

steppers don't really turn particularly

smoothly and since there's no feedback

you kind of have to add a tachometer or

a spin sensor to make sure that you

aren't missing steps I realized that the

rotor on this thing is not particularly

heavy so it's sort of a known

acceleration profile it's unlikely that

you'd miss steps but even still you'd

probably want some feedback so I

decided not to use the stepper motor and

then that leaves you know you could just

use a plain old DC motor in fact in my

previous spin coater this was the older

model I just used this old cheap DC

motor egg out of an old cassette deck or

something like that and I had that same

aluminum rotor pressed on to the shaft

here and this thing sat down in here

like this and I had a little bit more of

a this thing was a little bit taller I

cut the stop to make the the new shield

but anyway the it's not quite enough

power would be nicer if it accelerated

and decelerated with more control so

that was out another good idea is to use

a hard drive so when thinking about

stuff that already exists in the world

that kind of does what we want a hard

drive is actually pretty close so this

will get up to you know 7,000 rpm no

problem it's even got this nice bearing

system so that the thing spins smoothly

and it even a hoody has like a disc

shape on the front and the motor is

built into this nice aluminum housing so

we can kind of you know bolt this down

it'd be great and in fact if you go on

eBay there's a company selling low-cost

spin encoders made out of hard drive

motors and when I say low-cost I mean

like five hundred to a thousand dollars

compared to what the semiconductor

industry charges for these things which

is you know probably tens of thousands

there's another nice feature about these

these often have a solid spindle so this

particular one doesn't but on some hard

drive models the center of the spindle

actually doesn't spin because it goes

all the way through the motor to the

bottom and the cool thing about that is

if you attach a vacuum hose to the

bottom you can put a rubber o-ring on

the top and then when you put your glass

microscope slide down on that you can

use vacuum to hold the microscope slide

down and that gives you this nice

convenient vacuum Chuck so I liked that

idea

however these motors still don't have

quite enough power so you know your 7200

rpm hard drive may take you know five or

ten seconds to come up to speed and

that's actually about right but when I

started this project I thought I needed

to have much faster acceleration to have

a good spin coater and in a minute I'll

show you this thing connected

with the debug port and it's actually

pretty impressive how quickly this thing

can change speeds another slight problem

with using a hard drive motor is that

this is a four wire brushless DC motor

and it's wired up in what's called a Wye

configuration so the four wires are one

two three and four

and obviously it's called a Y because it

looks like that but most of the

brushless DC motors that are built for

quadcopters and similar things are a

three wire and it's called a Delta

configuration because it looks like a

Greek Delta and so the one two three

wires there and these are not really

interchangeable you can sort of get away

with it a little bit but generally not

really and also the coil resistances for

these are generally not quite the same

as they are for quadcopter motors so it

is and then you know later on you'll

find out that the the controllers that

they make for these things are so cheap

that it's just silly not to use them so

I decided not to go with the hard drive

motor if you go to a site like hobbyking

or one of the places that sells a whole

bunch of stuff for making your own quad

copters you'll find the prices on these

things are just really low I mean this

was probably ten dollars or something I

think they even have small motor

controllers that are even under ten

dollars and it's kind of silly because

if you go to digi-key and just look up

the parts like if you just buy all the

FETs that to make this or even though

you know a monolithic chip that's got

all the fats in there even that's going

to get close to ten dollars just in

parts and so it's kind of silly to not

buy this since it already has the

firmware it already has the controller

the capacitor I mean everything and then

the motor itself is ten to twenty

dollars and it's known to work with it

so you kind of are guaranteed a working

system just with these two parts if you

wanted to take a simple approach you

could just use these parts as they are

and these motor controllers are designed

to be controlled by this you know servo

standard so it's three wires ground

power and the servo signal and the servo

signal is just a pulse width it varies

from I think half a millisecond up to

one and 1/2 milliseconds and that sort

of indicates the throttle range

so you could totally connect this right

up to your microcontroller and people

have already written servo libraries so

you can just tell it how much in

percentage you want and this thing will

everything will work just fine so

there's almost no tweaking to do

although I wanted a couple extra bits of

functionality one of them is that I

wanted this thing to slow down on

command so since this is built for a

quadcopter there really isn't any need

to break the motor so if you you know

lower the throttle just the air

resistance of the propeller that this

thing would normally be connected to it

will slow it down but you can actually

configure these things to the engine

braking I mean regenerative braking and

even just full braking and luckily

enough the community is really well

developed around these things in fact I

don't know of any other product that

actually lists a hex file on the package

it says afro and FedEx and at first I

was thinking you know what how would

they just put the name of the hex file

on a package I mean what does that even

mean and then you realize that you're

entering this entire like huge community

that's very very well developed where

there's a lot of jargon going on and it

takes hours just to figure out what's

going on but basically the hardware has

become very standardized and lots of

folks have written their own firmware

and modding it is super common and it's

actually very well documented it just

takes a while to get going so take a

look at the description of this video

and I'll put links that will save you a

lot of time if you're interested in

modifying the firmware for one of these

you know for better or worse it is

written in assembly although again it is

fairly well documented another

interesting bit is that some of these

are made to be programmable over the

servo wire so with just three

connections you in theory can send a bit

stream over the control wire if you give

it the right sequence and someone even

wrote a Chrome extension such that you

can flash your firmware through Chrome

just with this one connection going to I

think they sell it a little USB

programmer so I tried it using an

Arduino as the programmer you can also

connect this to an Arduino and use that

as the programmer but it didn't work in

fact it actually ruined my device and

luckily I was able to

but it did actually stop it from working

so I can't endorse that route but

luckily what I did is just on this

particular board they've actually broken

out the in circuit programming port and

so these yellow wires here are going to

a programming header and again I just

used an Arduino as my programmer

compiled the assembly downloaded the

firmware to this thing and everything

worked great so I'll put details to that

in the description so here the mods that

I made to this thing in the assembly

firmware one is that instead of

controlling it over this you know servo

half millisecond timing pulse you can

actually configure this thing to accept

I squared C commands this is pretty cool

since you could actually potentially

have you know five or ten of these motor

controllers in a project and control

them all of them over the I squared C

bus from your microcontroller or

whatever you've got so that's cool and

then also instead of just you know

relying on the timing accuracy of

microseconds to get the signal you want

if you're actually giving it the value

you want over I squared C you can be

much more accurate and much more

reproducible so that's good and then

also I wanted this thing to slow down if

I gave it a slower speed than where the

motor was currently spinning like I said

for most quadcopter applications that

you know engine braking doesn't really

make any sense because as soon as you

lower the throttle it'll slow down but

for RC car applications sometimes you

want regenerative braking so that's a

switch in the code that's relatively

easy to flip also if you give this thing

the command of zero speed it can do a

much more aggressive braking thing so

instead of regenerative braking all the

way down to zero if you give this a zero

it will actually you know essentially

short out the motor windings in the

controller so that it will decelerate as

quickly as possible the difference is

that when it's regenerative braking it's

still commutated so that the thing knows

where the motor is where the rotor is

and then you can speed back up quickly

if you want if you give it the command

of zero that will actually stop

commutation so it no longer knows where

the motor is is it's just going to try

to slow it down as quickly as possible I

should add that a lot of these motors

you know hobby brushless DC motors come

in two flavors censored and sensorless

and censored doesn't mean it tops like a

sailor it just means that they have Hall

effect sensors in here so that the

controller can know the position of the

rotor at all times and if it knows that

then it can apply the current to those

three windings in such a way that it can

always make the rotor spin exactly in

the way that it should to get to get a

decent rotation with a sensorless motor

if this rotor isn't spinning there's no

electricity coming out of these things

and with no Hall effect sensors the

controller has no idea where the rotor

is so the only thing it can do is just

give it essentially a random pulse and

then wait for a minute and see if the

spinning rotor induces a voltage on the

unused pin and then it can figure out

where the rotor is based on the voltages

that it's creating just from its spin so

a lot of times you'll see one of these

motors start up it'll actually go

backwards for about a half turn and then

the controller realizes it started it in

the wrong direction but once it's moving

then it knows where the rotor is and it

can speed up again so the sensor sensor

lists motors are a bit more common and

cheaper and for applications where this

is not connected like you'd want a

censored motor if you were driving a

bicycle or a vehicle because the wheel

is in contact with the ground and it

doesn't really have the ability to just

kick it backwards for a half turn to see

where the rotor is so it kind of needs

to have a good way to accelerate from

zero for a quadcopter application it's

just connected to a propeller that's

just sitting in air so it doesn't really

it's easy to get the motor started in

retrospect I would probably try to go

for a censored application for this

thing but another challenge was getting

a motor that doesn't spin too quickly so

these things are designed to be

connected to small propellers and they

spin very fast you know 10,000 20,000

rpm even but I wanted to go slow so when

I was dispensing the fluid on here you

know 3 or 400 rpm is fine and getting a

motor that actually goes that slow is

tricky I thought I'd point out another

bit of circuitry before we move on this

is kind of a weird little device it's a

potentiometer voltage divider and the

output of the voltage divider is connect

to the gate of a pretty beefy and FET

and then the source of the end fed is

connected to ground and the drain is

connected to VCC basically the eight

fold output of that power supply and so

since I mentioned I wanted this thing to

be able to slow down if I commanded a

lower rpm then it's currently spinning

it has to do something with all the

energy that's currently in the rotor and

since it's continuing to commutated

can't short out the motor windings

because that would prevent the

controller from seeing where the motor

is so what what ends up happening since

it's basically a regenerative braking

system all that power that's in the

rotor all the energy that's in that

stored in that spinning rotor has to go

back into the power supply but that

eight volt switch mode power supply is

not too happy about it in fact it's not

able to sync much current at all so

there has to be some way of getting rid

of that excess energy so this what this

is is basically a programmable Zener

diode so in normal operation the N FET

is not turned on at about seven or eight

volts but as the voltage Rises it

eventually turns the N FET on and starts

conducting eventually looks like a short

if the voltage gets high enough so I

don't know if that's really production

quality I don't know if I would put that

in real production circuit in fact I've

never seen anything quite like that

before but it is very simple and it does

work very well I haven't tested it over

temperature stability or anything but

let me know what you think about that

part of the goal this project was just

to write a really tight PID control loop

for this motor system so that I could

command any rpm and get it to go to that

speed very quickly even though it turned

out for spin coders it's not critical to

have a really fast ramp rate so I'm

going to control this through the serial

interface and just command it to go to

1000 rpm so you can see it's starts up

and does just fine try 2000

it manages to reach the speed very

quickly and comes to a standstill so

when I command a zero speed then it's

using full braking and it stops

commutated but if we go from say 2000

down to 1000 then that's essentially the

regenerative braking thing where that

funny circuit is absorbing the powers

try that there is 0 to 2000 if we go to

0 or if we go to 1000 it's not quite as

quick and part of that is because the

circuit is not really designed for

regenerative braking and so it's it

doesn't pull as much energy out of the

system as you know as it could but to go

up to 4000 it's not quite as snappy

because I've limited the total throttle

setting just because I don't really need

to go that fast but it is kind of neat

to see the thing go to its extreme

perform performance limits ok well let

me know if you have any questions about

that and I will see you next time byeearn skrill money, best way to earn money from home, make instant money online absolutely free, trusted online money making sites, online income site, best online earning, money online, earn money from home, earn dollars online, earn money online, earn money online 2019, earn money online by typing pages, earn money online daily, online work at home and earn money, online earning, earn money online free, online money earning sites, earn real money online, e commerce ideas to make money, easiest way to earn money online, best way to earn money online, make money from home, make money online free, money making sites, earn from home, real ways to make money from home, online income ideas, make real money online, top online earning websites, earn money online fast, top 10 money earning websites, earn money without investment, earn money online for students, best sites to earn money, make money online 2019, earn easy money online, earn money online instantly, real money earning sites,