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Imperf3kt
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Seeking guidance with powering motors

Mon Feb 04, 2019 1:45 am

I'm looking to create something that requires a fair amount of torque so I rigged up a simple BC337 transistor connected to pin 12 with a 1k Ohm resistor which I used to switch a 4.5v motor on and off with a capacitor across it.

While this worked, it was not strong enough to do much other than power a fan, so I moved to 12v.
Unfortunately, my 12v motor needs about 1.5A and the BC337 I was using is only good for 0.8A
I also had different plans for it, so thought perhaps I could substitute four 3v motors in series.

In my search for another transistor I could use, I found I have a few MJE3055T and MJE2955T bipolar transistors in a TO-220 package.

I looked up the datasheet and found them rated for 10A 60v.


I've made this circuit which I think should work, but I have no formal education in electronics, so I am unsure of a few things.
Image
The four separate motors will be driving a single shaft to increase torque.

My first question is obviously, am I missing anything? As I understand it, I need the diode to take care of back emf when the motors switch off. The capacitor is probably not necessary and I am currently using an electrolytic, but I read somewhere that I should use a polymer film capacitor instead.

The other thing I am unsure of is the values, how do I know what size resistor I should use, what diode to use etc?

Is there anything else to consider?

Should I add another diode before M1?

I'll be using python to create the code to run the motor and don't require help with that side of things.

I appreciate any help given.
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Gavinmc42
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Re: Seeking guidance with powering motors

Mon Feb 04, 2019 3:02 am

Consider Gain, bipolar transistors are current amplifiers.
Current into the base is amplified, unless you use a darlington arangement you may not get enough current.
Diode is backwards, you will let the smoke out.

Most people use mosfet transistors for this reason.
For motors it is easier to use motor drivers.

Your circuit is a bit unconventional, that make it harder to check.
More torque? Just use more gears.
And 3V toy motors are basic crap motors, you can get the same motors with 12v windings so they draw less current and last longer.
Look for ones with carbon brushes, they last longer again and will have better torque figures.
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Imperf3kt
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Re: Seeking guidance with powering motors

Mon Feb 04, 2019 6:13 am

Thanks for the info. Looks like I need to review things as I feared.

The reason I wanted to use four motors instead of one geared motor was because as I understand it, a geared motor will sacrifice its RPM in order to generate the extra torque and I need around 200-3000RPM. I suppose what I had on hand wasn't the best choice though, so I'll review that.

As to using a motor driver, while it would simplify the process, it does more than I need as I only need to drive the motor in a single direction. Plus, I had some parts lying around that might do the job, so thought I'd use those before spending anything.



I'll have to go back to the drawing board, thanks for your input.
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Gavinmc42
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Re: Seeking guidance with powering motors

Mon Feb 04, 2019 8:03 am

Use a mosfet transistor.
You can PWM a gpio, 50% means 12V looks like 6V to the motor.
Motor drivers normaly have current limit, stops the motors from blowing up.
But if you blowup a 3v mtor on 12v if nothing has melted then you can cut off the windings and rewind with smaller wire for 12V.

Smallparts/Minibearings is my motor supplier, can get higher voltage hobby motors to replace those high current toy motors.
Higher voltage, lower current also means slower speed and higher torque.
Brushless motors are rated in k/v, ie RPM per volt.
This is determined by the number of turns on the rotor/stator.

You can fit more turns by using smaller wire and toy/hobby motors like Mabuchi can tell you that is their specs.
https://www.mabuchi-motor.com/product/k ... tions.html
wire size is in factions of mm, so 11 = 0.11mm
Toy motors will have 3 poles, industial ones may start at 5 poles.

Motors have a fairly wide voltage range, if unspeced you can get an idea by looking at the wire size or measure the resistance.
More turns = higher resistance = higher voltage.
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drgeoff
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Re: Seeking guidance with powering motors

Mon Feb 04, 2019 8:53 am

As drawn, the motors will not turn on until the diode (which is the wrong way round) burns out.

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tlfong01
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Re: Seeking guidance with powering motors

Mon Feb 04, 2019 9:01 am

Imperf3kt wrote:
Mon Feb 04, 2019 1:45 am
I'm looking to create something that requires a fair amount of torque.

Power NPN BJT and MOSFET

MJE2955/3055 are usually for audio amplifiers or linear voltage regulators. They are not that good for power switching. You may like to consider the following power switching guys.

TIP120 Data Sheet
https://www.onsemi.com/pub/Collateral/TIP120-D.PDF

IRF540N Data Sheet
https://www.infineon.com/dgdl/irf540n.p ... e396cb199f

IRF540N/TIP120 Project Examples
https://www.raspberrypi.org/forums/view ... 4#p1415943
https://www.raspberrypi.org/forums/view ... 4#p1416412
https://www.raspberrypi.org/forums/view ... 4#p1416619
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tlfong01
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Re: Seeking guidance with powering motors

Mon Feb 04, 2019 9:29 am

Imperf3kt wrote:
Mon Feb 04, 2019 1:45 am
The four separate motors will be driving a single shaft to increase torque.

BLDC Motor and Gear DC Motors for Big Torque

For big torque at low speed, you may consider geared motors. For high speed you may consider 12/24/36VDC BLDC motors.

If you wish to control direction and speed, you might like to consider half/full bridge PWM motor drivers, and for precision stepping motors.

I would suggest you to goggle newbie tutorials before you start.

Last edited by tlfong01 on Mon Feb 04, 2019 11:47 am, edited 1 time in total.
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OutoftheBOTS
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Re: Seeking guidance with powering motors

Mon Feb 04, 2019 10:58 am

U can get these dual h-bridge very cheap that will drive larger motors https://www.aliexpress.com/item/Special ... st=ae803_5

They will drive larger motors up to 46v and 4 amps, for datasheet see https://www.st.com/en/motor-drivers/l298.html

Do be aware the larger the current the H-bridge is rated for the higher the forward voltage (lost power) thus the big heat sink

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tlfong01
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Re: Seeking guidance with powering motors

Mon Feb 04, 2019 12:00 pm

Imperf3kt wrote:
Mon Feb 04, 2019 1:45 am
In my search for another transistor I could use, I found I have a few MJE3055T and MJE2955T bipolar transistors in a TO-220 package.

Motor Project Functional Specification and User Requirements

Let me summarize what I have read so far. What you wish is the following:

1. High torque ? motor
2. High speed (200 ~ 3000 rpm)
3. One direction rotation
4. Use available parts if possible
5. Circuit design references


One critical thing is the torque. You may need to let us know more details about your load, for example, is it a 1kg metal ball, 1 meter from centre of shaft, or 1 mg plastic ball, 2cm from shaft?

If your load is heavy and you want high speed, you might need to consider a more powerful 200VAC induction motor, controlled by an electro-mechancal relay rather than a transistor.

For circuit design help, I usually recommend electronics-tutorials.ws:

DC Motors
https://www.electronics-tutorials.ws/io/io_7.html

Bipolar Transistor as Switch
https://www.electronics-tutorials.ws/tr ... ran_4.html

MOSFET as a Switch
https://www.electronics-tutorials.ws/tr ... ran_7.html

Relay Switch Circuit
https://www.electronics-tutorials.ws/bl ... rcuit.html

Update 12:49PM TUE. 2/5/2019 Powerful Geared Motor

I once played with Aslong JB37-520 and found it OK.


https://penzu.com/p/a25b1076

Last edited by tlfong01 on Tue Feb 05, 2019 4:51 am, edited 2 times in total.
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drgeoff
Posts: 9587
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Re: Seeking guidance with powering motors

Mon Feb 04, 2019 1:11 pm

Imperf3kt wrote:
Mon Feb 04, 2019 1:45 am
I'm looking to create something that requires a fair amount of torque so I rigged up a simple BC337 transistor connected to pin 12 with a 1k Ohm resistor which I used to switch a 4.5v motor on and off with a capacitor across it.

While this worked, it was not strong enough to do much other than power a fan, so I moved to 12v.
Unfortunately, my 12v motor needs about 1.5A and the BC337 I was using is only good for 0.8A
I also had different plans for it, so thought perhaps I could substitute four 3v motors in series.
If you want any electric motor to do most things other than turn a fan blade you need some gearing between motor and load.

MarkR
Posts: 154
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Re: Seeking guidance with powering motors

Tue Feb 05, 2019 12:11 pm

I don't know how big your system is, but I suggest using the N20 gear motors which are tiny, cheap, and have amazing metal gearboxes available at loads of different ratios.

Hint: Search the usual sources for "N20 gear motor"

As far as driver is concerned - it's much easier to use a readily made motor driver board. You could use one of the Pi "hat" boards, e.g. the Motozero which will pretty much eliminate any soldering, etc, and is almost idiot-proof.

I used the TB6612FNG dual dc motor driver board, which are widely available from the usual sources - it will require some wiring, as you will need to connect to two power supplies - one for the logic (5v, shared with the Pi) and another for the motor - do not confuse them. Also you will need to connect at least two signals per motor for bidirectional operation, and add a resistor to hold the STBY pin high. You might also want to hold the pwm signals high.

A ready-made driver board will have chips in which are already protected from back-emf or voltage spikes, and usually includes some bypass capacitors to soak up transient current etc.

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Mortimer
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Re: Seeking guidance with powering motors

Tue Feb 05, 2019 12:18 pm

Brushed motors connected in series is not ideal either. The current passing through a brushed motor is very choppy, and this passes through the next motor which adds its own choppiness and so on. They may turn, but I would expect torque at each motor to be way down on what it can do by itself on its own DC supply, the electrical noise will be horrible which might also manifest itself audibly through the motor windings too.
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Imperf3kt
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Re: Seeking guidance with powering motors

Tue Feb 05, 2019 1:47 pm

Thanks everyone, lots of things to consider and many things I was unaware of (or blindly ignoring by trying to use what I have)

I noticed a typo in my first post too, I wrote I wanted around 200-3000RPM, but this should have been 2500-3000. My laptop keyboard has been playing up, with several keys not working for a completely unknown reason (no, it's not dust, I suspect the driver is corrupt or failing)


Anyway, will have to rethink this before redesigning it and coming back for more input.
Weight is a small consideration, but not overly important.
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Gavinmc42
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Re: Seeking guidance with powering motors

Wed Feb 06, 2019 12:03 am

There is a type of DC motor that runs at lower rpm.
https://www.minibearings.com.au/store/p ... 166x320mm/

If you are person who pulls apart stuff to see how they used to work or just for parts, you will have run across this type of DC brush motors.
Tape players, CD/DVD etc

The normal toy/hobby motor will have a RPM 10,000 plus, these are longer than their diameter.
The large diameter short case motors have lower RPM and more torque.

Gernerally a motor that runs from 3-4.5 even 6v I regard as a toy and annoying becuase you need more reduction gears.
Plus they wear out quick, 12V + and carbon brushes is the minimum for good robots.
But if you want to make flying things go brushless everytime, much better power to weight ratio.

There are exceptions, Swiss/German precision motors but they cost many $$ :D
Someone needs to make a simple low cost brushless motor driver for those CD/DVD motors that just get thrown away.
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tlfong01
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Re: Seeking guidance with powering motors

Wed Feb 06, 2019 4:36 am

Imperf3kt wrote:
Tue Feb 05, 2019 1:47 pm
Weight is a small consideration, but not overly important.

Motor Torque vs Speed vs Current vs Efficiency

Well, motor torque is a big consideration and overly important.

I used to fry motors and gear boxes because I ignore the torque thing. If a motor is overloaded, it cannot move, and the stall current is a couple of times than no load free rotating current. And the plastic and even metal gears crash, ... :mrgreen:


Voltage, current, torque and speed in DC motors - Electronics StackExchange
https://electronics.stackexchange.com/q ... -dc-motors

Pololu Motors and Gearboxes
https://www.pololu.com/category/22/motors-and-gearboxes

My DC Motor Journal
https://penzu.com/p/a25b1076
...
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tlfong01
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Re: Seeking guidance with powering motors

Wed Feb 06, 2019 6:43 am

Imperf3kt wrote:
Mon Feb 04, 2019 1:45 am
what diode to use?

Back EMF and Flyback Diode Selection

You might like to read my penzu journal on flyback diode selection.

https://penzu.com/p/5f1ae63c
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tlfong01
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Re: Seeking guidance with powering motors

Wed Feb 06, 2019 6:57 am

Imperf3kt wrote:
Mon Feb 04, 2019 1:45 am
I found I have a few MJE3055T and MJE2955T bipolar transistors
I looked up the datasheet and found them rated for 10A

2N3055 vs IRF540N for Power Switching

2N3055/MJE3055 is not good for power switching, because their 'on/contact resistance' is high. At 10A, the Vcesat is 3V, which means the power/heat energy loss is V * I = 10A * 3V = 30W. So you need a huge heat sink.

For IRF540N, the on resistance of 0.04R, so at 10A, heat dissipated is V * I = (I * R) * I = I^2 * R = 10 * 10 * 0.04 = 100 * 0.04 = 4W only.

Linear vs Digital Audio Power Amp and Regulated Power Supply

Many elegant HIFI guys hate digital audio power amp and power supply because they think D type power amp and switching PSU leaks out high frequency (100k+ Hz) signals which are disturbing to their high class ears. (Some extreme ones even hate solid state transistors and insist to use noiseless vacum tubes! :mrgreen: )

Not too many years ago I wanted a no switching noise PSU and I indeed use 2955/3055 to assemble a linear regulator power supply for my noise sensitive projects, ...


https://penzu.com/p/63c0be90
...
I am an electronics and smart home hobbyist.

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tlfong01
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Re: Seeking guidance with powering motors

Wed Feb 06, 2019 7:26 am

tlfong01 wrote:
Wed Feb 06, 2019 6:57 am
I found I have a few MJE3055T and MJE2955T bipolar transistors
I looked up the datasheet and found them rated for 10A

2N3055 vs IRF540N for Power Switching

2N3055/MJE3055 is not good for power switching, because their 'on/contact resistance' is high. At 10A, the Vcesat is 3V, which means the power/heat energy loss is V * I = 10A * 3V = 30W. So you need a huge heat sink! :mrgreen:

For IRF540N, the on resistance of 0.04R, so at 10A, heat dissipated is V * I = (I * R) * I = I^2 * R = 10 * 10 * 0.04 = 100 * 0.04 = 4W only.

Update 2019feb06hkt1917 - TIP120 Heat Loss
TIP120 VCE(sat) is about 4V at 5A, so would consume 20W at 5A.

Linear vs Digital Audio Power Amp and Regulated Power Supply

Many elegant HIFI old ones hate digital audio power amp and power supply because they think D type power amp and switching PSU leak out high frequency (100k+ Hz) noise which is disturbing to their high class ears. (Some extreme hifi fans even hate solid state transistors and insist to use noiseless vaccum tubes! :mrgreen: )

Not too many years ago I wanted a no switching noise PSU and I indeed used 2955/3055 to assemble a linear regulator power supply for my noise sensitive projects, ...


https://penzu.com/p/63c0be90

PS - When I chat with the young ones, I usually pretend to be also a young one:

..."Ah, I only started my embedded electronics hobby with Arduino Decimilla,
...and I never heard of 555, 3055, ..."
:mrgreen:


The Young Ones - Cliff Richard - 5,653,082 views
https://www.youtube.com/watch?v=BxNohANhJiA
...
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Imperf3kt
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Re: Seeking guidance with powering motors

Wed Feb 06, 2019 7:37 am

Gavinmc42 wrote:
Wed Feb 06, 2019 12:03 am
There is a type of DC motor that runs at lower rpm.
https://www.minibearings.com.au/store/p ... 166x320mm/

If you are person who pulls apart stuff to see how they used to work or just for parts, you will have run across this type of DC brush motors.
Tape players, CD/DVD etc
The motors I was planning to use look very similar to those. But I did look up their data sheet and they specify a voltage of 3-4.5v DC with a maximum RPM of 3500
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tlfong01
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Re: Seeking guidance with powering motors

Wed Feb 06, 2019 11:07 am

tlfong01 wrote:
Wed Feb 06, 2019 7:26 am
2N3055 vs IRF540N vs TIP120 for Power Switching

AWG22 Wires for Heavy Current Motors

For powerful motors, you also need to use heavy duty PSU and wires, as described in the post below, otherwise, all the power transistor, PSU, and (cheapy) connecting wires would heat up and melt down. :mrgreen:

https://www.raspberrypi.org/forums/view ... 4#p1425304

https://penzu.com/p/6dac4ae6
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