Help with Bidirectional Motor Driving with Voltage Regulator

[Eddiie]

Hello everyone, this is my first post and it is because I am stuck with a project.  Hopefully someone can help me out.

This is such a simple task, can't believe I'm having issues.

All I want to do is provide reverse to my regulated motor.  ? 

I have a 3 volt motor,  I have a 3.3 volt Regulator.    I have 12 volts.    This works great in one direction, but not in reverse.
Makes sense.

So, I added some diodes and another regulator to handle the reverse polarity (at least that is my intention) but it does not seem to work.    When voltage is applied in one direction, I get 3.3 volts, when the power is reversed I get some strange results...  Seems like it starts at 6 volts and ticks down 0 over time..    I have only tested with a volt meter and no load.

So, my question is simple...   Without bulding a motor driver (which already exists but @ 12 volts) how do I make this work at 3 volts in both directions?   Make sense?

When assembling this, it looks like all I have to do is flip one of the regulators 180 degrees from the other one, that way the output pins line up and the input and grounds are reversed.   I protected those pins with rectifier diodes but think I have created some sort of feed back loop that allows current to flow into the input of the intended non-active regulator..  hard to explain.

Driving me crazy.

Really appreciate it.

Eddiie

[newInRobotics]

hard to explain.

That's why engineers use circuit diagrams  Showing us one would help a lot.

Now, to get negative voltage regulated, You cannot simply turn positive voltage regulator around and hope it will do regulation form -12V to -3.3V, as You probably figured out - it does not happen. For negative voltage regulation You have to get special negative voltage regulator.

Smarter solution would be to use H-bridge; You can either build one from transistors, or buy one ready made like L298N. Then, You feed 12V to 3.3V regulator and feed 3.3V to H-bridge.

Even smarter solution would be to use microcontroller and dump voltage regulator which is very inefficient. With uC You can detect current running through Your motor and regulate it by changing switching frequency of an H-bridge. This is very efficient method to drive motor from higher voltage rated power supply.

If You have no experience - start small: get 2x 1.5V batteries or 1x Li-Ion 3.7V battery and get/build H-bridge. This way You can understand how it all works without blowing Your budget.

[Eddiie]

heh diagram.  I can try but No much of an artist.

It might be easier to use a 12 volt motor.  instead.  I swear, I've seen this same motor case in a 12 volt form.

I like the H-Bridge but it looks over kill for my application.    Although, it does appear to do exactly what I need it to do, I see all the parts there anyhow.  Negative voltage regulator sounds promising.  ?

Thank you.

Wow, posting on here is very difficult.

[Soeren]

Hi,

If you just need polarity reversal (and no speed control) a switch or a relay could provide it. To switch both lines over, you need a 2-pole change-over (DPDT) switch (or relay).

[Eddiie]

Hi Soren,

It is a little more complicated than a simple reverse.   Can I attach pictures to messages?  It might help.

Ah I see attaments link.  Ok give a few hours.  Got a few other things to wrap up first.

Thank you,
Eddiie

[Eddiie]

Alright.

Here's the mess I have..

Just need the motor to spin one way when power applied in one direction, and the opposite way when power applied in the opposite direction.

Power source is 12 volts, motor is 3 Volts.

[Eddiie]

Here is a picture of the actual motor.  Seems like it might be easier to just find a 12 volt version.. But then I won't learn anything.

[newInRobotics]

Do You require speed controll?

Do You require electronic switch (say operated by uC), or manual switch (hand operated) is fine?

[Soeren]

Hi,

Here's the mess I have..

My sincerest condolences

Just need the motor to spin one way when power applied in one direction, and the opposite way when power applied in the opposite direction.

Power source is 12 volts, motor is 3 Volts.

I hope you made a few drawing errors, as, in your drawing, you effectively cuts out both regulators and feeds the 12V directly to the motor.

I think I get what it is you want (correct me if not)...
You have the 12V controller and for some reason you want to run a 3V motor off it. You want the controller to "see" the motor at all times, to utilize the control parameters of the controller fully.

This will be easily done with a series resistor and nothing else. It will lower the torque of the motor a little during hard loading, butyou could compensate for that by calculating the resistor for hard loads and if the unloaded speed gets too high, a couple of back-to-back power zener diodes can be used (over the motor) to keep lightly loaded voltage down (although I don't think you'll find that necessary.


Measure the current when the motor is running normally (perhaps lightly loaded) on 3V.
Calling this current I_motor, calculate the resistor...

R_series = (12V-3V) / I_motor

And find the needed minimum wattage of the resistor by...
W_Rseries = (12V-3V) * I_motor

If the motor takes eg. 500mA, the calculations looks like this:
R_series = (12V-3V) / 0.5A = 18 Ohm

W_Rseries = (12V-3V) * 0.5A = 4.5W

So, in that example, you'd need an 18 Ohm resistor of at least 4.5W (5W is a standard value)
If it resistance value doesn't turn out to be a standard value, your options are to either go with the nearest smaller standard value giving a somewhat higher voltage (calculate to see if it's too high), choosing the nearest larger value which will lower the available voltage to the motor, or connecting more than one resistor (in series and/or parallel) to get the exact value).

Things to ask yourself:
Why this low voltage?
Small motors are cheap, a 12V motor could be substituted.

Does it matter if it goes a little faster or a little slower?
Motors can be fed a certain range o voltages, just make sure it doesn't get too hot - if you can hold it comfortably in your hand (40°C max), it's will handle it. life expectancy goes down with heat - around a 50% reduction in life time for a 10°C temperature increase.

[Eddiie]

Do You require speed controll?

Do You require electronic switch (say operated by uC), or manual switch (hand operated) is fine?

Do not require speed control.  Simply want to drive 3 volt motor in 2 directions using 12 volts and a Voltage Regulator.

Manual switch is fine.     

[Eddiie]

Hi,

Here's the mess I have..

My sincerest condolences




haha thanks


On to the rest of your post,  Soeren sounds like you got it right on.     I am actually mating 2 different products to make a more controllable one.  Resistor!   Ok reading it now.    Thank you in advance!!

[Eddiie]

I screwed up the Quote Tags....



I hope you made a few drawing errors, as, in your drawing, you effectively cuts out both regulators and feeds the 12V directly to the motor.

I think I get what it is you want (correct me if not)...
You have the 12V controller and for some reason you want to run a 3V motor off it. You want the controller to "see" the motor at all times, to utilize the control parameters of the controller fully.

This will be easily done with a series resistor and nothing else. It will lower the torque of the motor a little during hard loading, butyou could compensate for that by calculating the resistor for hard loads and if the unloaded speed gets too high, a couple of back-to-back power zener diodes can be used (over the motor) to keep lightly loaded voltage down (although I don't think you'll find that necessary.


Measure the current when the motor is running normally (perhaps lightly loaded) on 3V.
Calling this current I_motor, calculate the resistor...

R_series = (12V-3V) / I_motor

And find the needed minimum wattage of the resistor by...
W_Rseries = (12V-3V) * I_motor

If the motor takes eg. 500mA, the calculations looks like this:
R_series = (12V-3V) / 0.5A = 18 Ohm

W_Rseries = (12V-3V) * 0.5A = 4.5W

So, in that example, you'd need an 18 Ohm resistor of at least 4.5W (5W is a standard value)
If it resistance value doesn't turn out to be a standard value, your options are to either go with the nearest smaller standard value giving a somewhat higher voltage (calculate to see if it's too high), choosing the nearest larger value which will lower the available voltage to the motor, or connecting more than one resistor (in series and/or parallel) to get the exact value).

Things to ask yourself:
Why this low voltage?
Small motors are cheap, a 12V motor could be substituted.

Does it matter if it goes a little faster or a little slower?
Motors can be fed a certain range o voltages, just make sure it doesn't get too hot - if you can hold it comfortably in your hand (40°C max), it's will handle it. life expectancy goes down with heat - around a 50% reduction in life time for a 10°C temperature increase.

---------------------------------

Wow.  ok I need to measure current.  That is not voltage, correct?  If not I'll need to know how to measure that.  (I'll Google it)

Here are some links to the motor controller I want to use...  Note, this is not a traditional Robot but has to do with automation and having a machine do something without a human.   

Motor Controller (I have a Zwave enabled home) and purchased 5 of these  $$$ -

Image:  http://www.asihome.com/images/esi-dbmz.png
Specs: http://www.asihome.com/ASIshop/manuals/DBMZ_Specs.pdf
Quick Setup: http://www.asihome.com/ASIshop/manuals/DBMZ_Quick.pdf
Advanced Manual (Programming)  http://www.asihome.com/ASIshop/manuals/DBMZ_Advanced.pdf

Product Detail Page - http://www.asihome.com/ASIshop/product_info.php?products_id=3475

I am trying to mate that with this product:   http://www.intellitilt.com/


For the record, the folks at ASI Home (the Reseller) are a bunch of great people.   The Intellitilt folk(s) are pretty cool too.

In fact, the Intellitilt is pretty much complete by itself.  I just want my home controller to control it, not the solar panel.

I hope this clears things up but does not discourage the help I been getting.     I was into Robots about 15 years ago, had a few Hero's and Jr.s  a few others in the collection but was frustrated by the limitations of the sensors at the time.   Seems like a whole new world now with PICs, microcontrollers all over the place, better sensors, etc.   Might want to circle back on this hobby some day.     Had an Aibo too...    They were all pre-made and a lot of machine code to dig into them, who has time for all that?       Now, it seems we've made several steps forward while still the BASICS apply..  Resistance, Capicatance (?), etc etc.   Smaller, faster.   Ok  Im rambing on now.    I'd love to get a basic circuits class  of some sort under my belt.  Been soldering for 30+ years..   
Shutting up.

As always, thanks for your inputs!!

[Soeren]

Hi,

Wow.  ok I need to measure current.  That is not voltage, correct?  If not I'll need to know how to measure that. 

It's not voltage. If you have a multimeter, it will have a currnt range as well and you just put the meter in series with the "circuit" to measure current. Perhaps the meter has a socket for current next to the socket for voltage measurements, but usually this is only needed on the highest range.
Remember to set it back to voltage range when done, or you may short out something the next time you need to measure voltage (a current meter is more or less a short).

I'd expect something like 0.3A to 1A on that motor (when loaded by the gearbox and blinds), but given that this is made to be driven from a rather small solar panel that probably charges 1..2 NiMH cells it might be less, as those panels don't generate enough power for even the short term use of a motor with that specs during an overcast or rainy day. So guessing on the current would be ... guessing - you need to measure it.

(I'll Google it)

If only more people were like you

Note, this is not a traditional Robot but has to do with automation and having a machine do something without a human.   

Automation is the mother of robots and since it seems your application have feedback, you might call it a robot.

[...]
I am trying to mate that with this product:
[...]
In fact, the Intellitilt is pretty much complete by itself.  I just want my home controller to control it, not the solar panel.

Ah, OK.
Then a resistor is definitely the way to go!

The current when loaded will not vary significantly, but you'll have to measure it under its normal operating condition if you want to find the best resistor in one go.

Alternatively, you could get hold of a selection of resistors and find the best, but they need to be able to handle the power.

A so called L-pad (a wire wound potentiometer/variable resistance) as used on some speakers could be used as well, if you can get a model going to say 47..100 Ohm. They're made to handle a good bit of power.

You could use two 8.2V zener diodes back to back for a roughly 8.9V drop instead of resistors. They should be connected with either both cathodes or both anodes connected together like this -|>|-|<|-  or  -|<|-|>|- and the free ends connected in series with the 3V motor - they'd need to be rated for at least 9V*I_motor watts, so 5W zeners would work up to a current of roughly 500mA (0.5A)

I hope this clears things up but does not discourage the help I been getting.

Clears up a lot and does not discourage, on the contrary, it makes it easier to help when you know what it's all about

I was into Robots about 15 years ago, had a few Hero's and Jr.s  a few others in the collection but was frustrated by the limitations of the sensors at the time.   

You should have kept them - most of what's for sale of those Hero's makes me think they rebuilt them in gold plates.

Seems like a whole new world now with PICs, microcontrollers all over the place, better sensors, etc.   Might want to circle back on this hobby some day.     Had an Aibo too...    They were all pre-made and a lot of machine code to dig into them, who has time for all that?       Now, it seems we've made several steps forward while still the BASICS apply..  Resistance, Capicatance (?), etc etc.   Smaller, faster.   Ok  Im rambing on now.    I'd love to get a basic circuits class  of some sort under my belt.  Been soldering for 30+ years..   

Yes, the basics still hold true and even (a few) regular 10 year old kids builds robots these days - it is easier these days getting to the tools and there's more of them, not to forget the impact of information sharing through the web