Why replace the h-bridge?


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    Lightbulb Why replace the h-bridge?

    Hi All
    When the kids with the massive sound systems in their cars bolt an extra 2000 watts of speaker to the roof of the car they still use their existing CD player, all that they do to drive the new and bigger mess is replace the power amplifier with a bigger, more capable one.
    Why can this not be done in the CNC and Robotics world with regard motor drivers?
    If you have a little NEMA17 and you replace it with a MUCH larger stepper, the chances are that whatever lightweight h-bridge is there will probably get fried (maybe along with a whole bunch of other stuff.)
    Now falling around the internet trying to find an h-bridge to replace the lightweight one you have takes lots of time and these things are normally the same cost as your grocery bill.
    So why not simply add a "power amplifier" onto the existing pins that go to the motor and plug the motor (and the high power source) into that to do the heavy lifting?
    The reason I am asking is that I am trying to build a small proof of concept robot arm which will be powered by puny little RC servos so that I can develop and test a software design I am thinking of.
    Now these can be driven by small little .6 amp h-bridge chips but what happens when I go full size?
    At that point I will probably be using something like a windscreen wiper motor to get the power I need (using reduction gearing of course).
    That little .6 amp chip will simply explode the first time I power up the motor.
    So why can I not use a simple "POWER" amplifier between the existing output and my new monsters?
    And if I can, does anyone have some ideas about what to use and what all is needed?
    Anyone from South Africa (and probably a whole bunch of other countries) will know that once you have found what would be the ideal solution it is probably not available locally.
    Then if you buy it from overseas, the shipping kills you because it is in most cases it is well over the original price of the item and right there it becomes a "totally not viable" option.
    Call it a "power amp", "amperage booster", "high power booster" or whatever you wish, using the existing, dialed in and reliable h-bridge chip to drive the "power amp" would definitely be a lot cheaper than replacing the whole unit and it can probably be built using discrete components that are available locally, on its own board, with its own heat sink and maybe with its own fan to keep things cool.
    The guys with audio amp experience probably know how to do this so that the "sound" does not get distorted etc and this will probably work well using a minimum of parts and saving us a lot of pain and money.
    Anyone with ideas as to how to do this because I am at the point where I have to buy the h-bridge chips for the test bot and would love to use the low powered option (RC servos can run directly of an Arduino but 5? Rather not take the chance!!!) and have a viable path forward to the big motors that does not involve doing circuit rebuilds and tuning all over again.
    Thanks for reading and solutions would really be appreciated.

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    Default Re: Why replace the h-bridge?

    the problem when you add a H-bridge to an existing stepper driver is the control of the motor current

    normally the H-bridge is connected to the negative supply terminal via a low value resistor
    the volt drop across the resistor provides a measure of the motor current thats used by the control circuit

    how to add the current controlling feedback from the new H-bridge is the issue

    adding power amplifiers to audio systems or transmitters is easy by comparison

    John



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    Default Re: Why replace the h-bridge?

    Yes, if you need to amplify sound you can just swap the power amplifier stage with a bigger one to suit your needs. Never the less, you don't just swap the power transistors but a whole lot of other parts as well. I see it this way even with steppers. If you have drivers which can only manage small NEMA17 1A motors and you want to change the motors to NEM34 4A type then you simply swap your stepper driver stage to suit the new motors to something else. The problem comes when people are using small motion controllers with integrated drivers. In that case everything must be replaced.

    In your analogy to audio... if I wanted to install your 2000W speakers in my home I'd need to replace the whole HiFi because today my CD player, pre-amplifier, equalizer and power amplifier are all integrated in one box. When I was young all that were separate boxes (CD was not invented yet) so I could have installed your speakers easier back then.

    On the other hand... you are talking about a windscreen motor, and as far as I know, none of those are stepper motors, just pure analog brushed DC motors, and in those cases it is probably much easier, and in theory you would just need to replace a few parts, similar to a new power amplifier. Stepper motors are different.



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    Default Re: Why replace the h-bridge?

    Quote Originally Posted by A_Camera View Post
    On the other hand... you are talking about a windscreen motor, and as far as I know, none of those are stepper motors, just pure analog brushed DC motors, and in those cases it is probably much easier, and in theory you would just need to replace a few parts, similar to a new power amplifier. Stepper motors are different.
    Sorry for the confusion - was thinking stepper when I should have been thinking servo but the same thought process applies weather you are driving a stepper or a DC motor using PWM.
    The coils take what they get in volts and draw what they need in amps.

    The project proof of concept will be using small RC servos, the final product after developing the software and hardware will use wiper motors (and a lot of gearing).
    I am just trying to figure out if I can use a small h-bridge chip during the development stage and simply add the higher amperage "power" section when it goes to full size without having to re-develop the circuitry.
    I'm not very good with electronics - I have blown over 30 PIC's the last time I tried using a soldering iron.
    But now I am confused !!!
    Are you saying that the h-bridge controls not only the average voltage using PWM but the amperage as well?
    As far as I know, the motor draws amps as it needs it - high if the motor is starting or stalling and low under a small load.

    But anyway, if the h-bridge (on a DC motor) is giving 50% voltage (lets say 6v) by using PWM then the amplifier should also give 6v - using the same PWM signal that it gets from the h-bridge output, the only difference is that the h-bridge can only handle 0.8 amps while the amplifier is able to handle say 20 amps.
    It amplifies the ability to handle higher current draw and simply follows the voltage it receives - in PWM or in "full on" mode in a 1:1 ratio - no step up or down for the voltage at all - just the maximum amperage available.

    So the word "amplifier" is probably misleading in a way - it is simply using the h-bridge output to make (maybe the same voltage, maybe not) more amps available.



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    Default Re: Why replace the h-bridge?

    if its OK that the motor current is only limited by the motor windings resistance

    how about adding complimentary emitter followers to your existing servo outputs - TIP41 + TIP42 ?


    Why replace the h-bridge?-possible-mod-h-bridge-jpg


    John

    PS

    just found this simple circuit of a stepper driver using 3 TDA2030 audio amplifier IC's !

    https://www.elektor.com/Uploads/File.../050246-UK.pdf

    Last edited by john-100; 09-08-2016 at 12:03 PM.


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    Smile john-100 : thanks for the information

    Hi John
    Thanks for taking the time to answer.
    I'm in South Africa and that adds a layer of complexity/BS/whatever that non South Africans won't believe.
    Quote Originally Posted by john-100 View Post
    how about adding complimentary emitter followers to your existing servo outputs - TIP41 + TIP42 ?
    I had a look for TIP41 and TIP42 (sourced locally) - nothing.
    Apart from AliExpress (not used them due to all the horror stories) who are selling 10 packs for about US$6.50 plus shipping US$2.11 (total US8.51) which makes it less than a Dollar each but as I said, a hesitant about buying from China
    Also they are rated at 6A 100V (a bit low on the amp side maybe??)
    Why replace the h-bridge?-rediculous-shipping-png
    I did find other suppliers and I'm adding a screenshot of an Austrian company so that you can see the BS we have to put up with - ZAR8.95 orabout 50p(UK) each but have a look at the shipping - almost 100 times the cost of the component which EASILY fit into a small shipping/padded envelope.
    It seems that some people sell at cost or even below and make their profit on ridiculous shipping markups.

    Quote Originally Posted by john-100 View Post
    just found this simple circuit of a stepper driver using 3 TDA2030 audio amplifier IC's !
    From what I could find out on Google, the TDA2030 is discontinued and all I can find were complete modules that use this device.

    I am going to Pretoria today and I will pop into RS Components and see what equivalents are available and what they cost.

    I like the example from Elector.Com but it seems (to my untrained eye) that the circuit still needs some extra "stuff" (flyback diodes, optoisolator, etc) and then the question is "will it work properly when given a 3v3 (Arduino DUE is NOT 5v) pulse?".

    Getting back to my "Amplifier" concept, I have just figured out something:
    Will it matter that the incoming voltage from the h-bridge is only 3v3?
    After all, it is a pulse and the timing of the PWM setup makes it "seem" like at a 50% cycle it is outputting 1.65 volts.
    So if the power transistors get pulsed at a 50% cycle and the supply voltage here is 12v then it should output 6v and be able to handle a lot more amperage.

    The reason that I am asking is that I had visions of having to set things up based on the pulse voltage maximum (3v3), figure out what the duty cycle was, do all sorts of conversions and stuff to be able to drive the power transistors.
    All of this would be a pain in the butt, apart from being TOTALLY unnecessary because when the power transistors get a signal, the shove out 12v and if there is no signal, the 12v dissappears.

    Which means that the "Amplifier" idea is nothing more than an on/off relay made using power transistors and not coils and contacts like a "normal" mechanical relay.

    Anyway, I really appreciate the mentoring so far and I am learning things - there is still a lot of "fog" blocking the mind but I will get there hopefully.

    Thank you a ton



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    Default Re: john-100 : thanks for the information

    Quote Originally Posted by MadAubrey View Post
    I did find other suppliers and I'm adding a screenshot of an Austrian company so that you can see the BS we have to put up with - ZAR8.95 orabout 50p(UK) each but have a look at the shipping - almost 100 times the cost of the component which EASILY fit into a small shipping/padded envelope.
    It seems that some people sell at cost or even below and make their profit on ridiculous shipping markups.
    Why aren't you checking more locally, like in SA?

    Why replace the h-bridge?-rs-south-africa-jpg

    http://za.rs-online.com/web/c/semico...3D746970343126

    Shipping costs R95 if you can wait a week. Why make it more complicated than necessary? You don't have to order from Australia or UK. You can probably also buy from eBay much cheaper.



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    Default Re: Why replace the h-bridge?

    Hi

    I have had a look at RS Components and see they stock the TBA2030 and TIP41 & TIP42
    also another pair of transistors I remember from the days I used to build audio amplifiers - TIP3055 & TIP2955

    what H-bridge circuit have you used for your initial tests
    some thing like the L293 or SN754410 that has logic level inputs ?
    note - the L293D had the output protection diodes the L293 does not


    John

    Last edited by john-100; 09-09-2016 at 06:40 AM. Reason: add ref to L293


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    Default Quixk update

    Hi all
    Its been one of THOSE days.
    Good news - I got 2 large photocopy machines and 2 small ones on my trailer - donated by a company that sells and maintains them.
    The manages says I must stick my head in again in about a month - should be all sorts of "nice" goodies in there.
    Quote Originally Posted by A_Camera View Post
    Why aren't you checking more locally, like in SA?
    I am - RS Components have a "slight" issue with their inventory numbers - bought & paid for 5 off 3v3 regulators (only sell in 5 packs) but they had 9v units in the bin.
    One of the other electronics component places looked at me as if I was speaking Klingon or something when I asked what h-bridge chips they had in stock - after getting a "higher up" involved (who knew what an h-bridge was) it turns out that they have NEVER stocked ANY type of h-bridge.
    Go Figure - one of the staples of the digital world and no stock - EVER !!!

    Quote Originally Posted by A_Camera View Post
    Shipping costs R95 if you can wait a week. Why make it more complicated than necessary? You don't have to order from Australia or UK. You can probably also buy from eBay much cheaper.
    eBay simply will not ship to SA for some reason or other - even sellers that advertise "world wide" - when you start the "lets pay" process, you get something like "unable to ship this item to South Africa" - I have tried to contact them but they seem to be like Google - just do not respond.

    Quote Originally Posted by john-100 View Post
    what H-bridge circuit have you used for your initial tests
    I have not yet done any testing because I can not buy ANY sort of h-bridge lower than 30A (at a very high price) for love nor money.
    Been riding around almost all day visiting wholesalers and electronics shops because their web sites are not very helpful and if you phone in the person starts trying to sell you bridge rectifiers instead of h-bridges.
    Sometimes the counter staff (in an electronics component distributor) do not even know what an h-bridge IS !!!.

    There is a flaw in the robot design that has to do with the fact that all motors are in the base and all joints are moved using belts, chains, cables or whatever.
    When one joint moves, all the joints above that joint move as well - not in space but in the angle of the joint.
    This is because as the "moved" joint angle increases or decreases.
    I may have mumbled something about this before...
    Example:
    if the angle of the first joint is 20 degrees and the angle of the second joint is 10 degrees then moving the first joint to 15 degrees will cause the second joint to move in relationship to the arm between the first and second joints because the position at which the belt is meeting the idler pulley and sometimes the winch pulley as well) is changing.
    BUT by using servos and placing the encoder on the actual joint this problem will be overcome as the servo on the second joint will automatically be corrected due to the angle of the second joint changing.

    Anyway I have one more component place to visit tomorrow (Saturday) down in Joburg south so lets hope they have some h-bridges at affordable prices and in single unit packaging.
    And then I have to start stripping the photocopy units which will be done in the trailer as they are 2 man heavy and I am just 1 old man - should be some great "stuff" there.
    Then I have to find a bunch of old printers for their optical encoder readers and try to make some encoder disks but that is for next week.
    I also bought a bunch of micro-servos to use when testing if the code actually moves stuff before I manage to get the arm built which is going to be a bit of a problem without ANY tools - the only tools I have to my name are those that I have bought in the last week - my entire life's worth of tools and equipment (small lathe/mill with a ton of tooling and inserts, drill press, bench grinder, power tools were chucked in a skip for me when I was not looking - I'm still livid about that and will be for a long while.........
    We are moving in 2 or 3 weeks so I do not think it would be wise to start building the test arm now - will probably get destroyed in the move anyway.

    It was HOT today and with all the running around that I did I am KNACKERED so its goodnight from me.

    Last edited by MadAubrey; 09-09-2016 at 02:09 PM. Reason: fixing the QUOTE code


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    Default Re: Why replace the h-bridge?

    Hi
    i am in the same boat as you are trying to find some thing the same, i also want to drive a wiper motor from a car for a extruder i am building for my 3 d printer,
    i have settled on a 12 v 20A dc motor controller, old school.Why replace the h-bridge?-112476_5mg-jpg
    I tell you if we can get one that plugs into an arduino board we will make money.



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    Default Re: Why replace the h-bridge?

    Have you tried Mantec electronics? Mantech Electronics | Leader in Electronic and Industrial Components, Tools, Test and Measurement,
    Also just down the road from them are these guys much more helpful, rse electronics, https://www.rseonlineshop.co.za/,

    i prefer to drive there and speak to them face to face,
    good luck.



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    Default Re: Why replace the h-bridge?

    Got some h-bridge chips from Mantec - thanks for the heads up



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    Talking Situation Report

    melvinbruce put me onto Mantech and I got the small h-bridge chips I was looking for.

    Stripped down the 4 photo copiers Monday, Tuesday, Wednesday - what a mission !!!

    But I got a boatload of FREE stuff - dc motors with big reduction gear sets (img below), nice bearings and oil-lite bushes and shafts, micro switches, optical sensors, 15 or so small steppers and a bunch of fancy brushless dc servos with commercial grade 20:1 metal geared reduction gearboxes (for which I can find NO INFORMATION on the web - fired off an email to the manufacturers Nidec Japan to see if they could help)

    Now I have 2 Venters full of stuff to dump ;>} , sore and cut hands and total confusion as to how they manage to get so much "stuff" into such small areas - how to actually disassemble them is still a mystery as I had to use a hammer on some of the plastic stuff and a tin snips on others just to get into the things. (and thousands of little screws).
    But I'll be wrapping it all in newspaper and putting it in boxes pending the move.

    The mission this week is to find some 5mm perspex or some other rigid plastic and make the base and arm sides and get them all drilled.
    Maybe I will have time to get something to use as the rotary axis between the bottom stand and the rotating base of the bot.
    Maybe I can find an old car McPherson strut with the bearings and all and cut what I need off of it and clean it up a bit - McGyver time....

    Speaking of McGyver, the DUE is 3v3 and just about everything else in the world demands 5v which is somewhat of a problem so I came up with this idea.

    Seeing that nothing I will be using is analog, only digital, why not use opto-isolators to do the switching from 3v3 (DUE) to 5v?

    Put the 3v3 signal into the opto and a 5v supply onto the other side - that way I will not have to find expensive 3v3 hardware or design/build fancy complicated convertors, just use what everyone else is using on their UNO/MEGA bots - just need to find the right ones at the right price....

    That should take care of most of the connections and the feedback to the DUE can be the same just reversing the opto - as long as it is not analog.

    So today, instead of going to look for the perspex I need, I have to sit around waiting for the electricians who came in to fix everything up for the COC but who buggered up more than they fixed, to arrive and fix their $#1t.

    Oh well, time to break out FreeCAD and try to make some drawings.

    Attached Thumbnails Attached Thumbnails Why replace the h-bridge?-dc-motors-gearing-jpg  


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    Default Re: Why replace the h-bridge?

    Hi there i been cutting my dust shoe from 5 mm perspex, i have some left over if you want i can cut it on my cnc for you, drop me a PM.



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    Default Re: Why replace the h-bridge?

    Hi Aubrey

    I've missed a few posts while my broadband connection has been off , due to a line fault

    in this from microchip -

    Why replace the h-bridge?-3_3vto5vanalogtipsntricksbrchr-pdf

    from page 19

    Why replace the h-bridge?-level-converter-p19-jpg

    another converter from sparkfun

    Why replace the h-bridge?-sparkfun-logic_level_bidirectional-pdf

    if you can't find fets like BSS138 with a gate threshold about 1 to 2V
    may be you could use a npn transistor buffer/ level translator

    John



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    Default Re: Why replace the h-bridge?

    Hi John
    Looks like a very nice circuit and I see there is also a 4-up board design out there.
    I love the bi-directional (if I understand it correctly) functionality and will definitely add it to my list of options.



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    Default Re: Why replace the h-bridge?

    Hi Aubrey

    originally I was looking to convert the 3V3 from the Arduino to 5V logic levels for the stepper drivers
    finding the bi-directional converter from sparkfun was a bonus - being able to convert 3V3 to 5V or 5V to 3V3 logic levels

    as its an open hardware project I thought there was a chance that a version could be made in South Africa

    John



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    Default Re: Why replace the h-bridge?

    Hi John
    Looks like a very nice circuit and I see there is also a 4-up board design out there.
    I love the bi-directional (if I understand it correctly) functionality and will definitely add it to my list of options.



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