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Thread: help on stepper motor overdrive

  1. #11
    Super Moderator T-1000 docel's Avatar
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    Nickel Metal Hydride (NiMH) batteries are the best bet, inspite of the cost. They have a very good size to power ratio and are far superior to Ni-Cd cells, in all respects. While Ni-Cd cells are good for high discharge currents, they have to be charge-cycled intelligently, or they will collapse after a few charge-discharge cycles.
    The cost of a AA Ni-MH 2700mAH is about Rs. 50/-
    docel
    ^Anything is possible..
    after YOU prove it!!

    http://bangalorerobotics.tripod.com

  2. #12
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    Default thanx

    thanx docel......
    can u tell me what is the voltage rating of those ni-mh batteries??? actually, my motors are slightly overweighted and so my voltage requirements is high....its slipping a lot on 12v so i am thinking of using 24v..... in this case using 20 batteries in series will be problematic from the point of view of weight......

    i am thinking of non-rechrgable batteries of 12v rating.... they cost about 15rs.... but i am not sure about its current ratings..... one of my friend say he used it for controlling a single stepper motor ( one like i a using) .... but he has to demonstrate the project only for 2 min and so he also do not know for how long it can drive..... also there was no load on stepper in his case ( stepper was resting on its back )...... so i am not sure if it will work for me...

  3. #13
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    Ashish,

    If motors are sleeping and not serving your purpose, then is not correct way to drive motors at 24V for prolonged time if they are rated for 12V. Motors may fail at any time when driven by almost double voltage. Also obviously you will need more number of batteries to get that much voltage which will add extra weight. There is no escape from this situation. Prefer changing the motors with the ones which have less winding resistance and you can drive them easily at 12V with limited batteries and also they will give sufficient torque.

    As energy stored per kg increases , cost of the battery increases. Ni-Mh/Ni-Cd will be best as they can provide huge currents.

    Non-rechargeable batteries are useless. During ur project development you will spend more on these batteries than purchasing new rechargeable ones !

    There is already lot of info available in forum/web regarding Ni-Mh batteries. Search a bit.
    For every minute that is spent in organizing, one hour is earned !

    http://elecrom.wordpress.com/

  4. #14
    Super Moderator T-1000 docel's Avatar
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    Ashish!
    15 rupees batteries dont work for high torque motors.
    The best is Nicd which have very low internal resistance. hence they will supply very high currents. I use 700mAh Nicd batteries for my 100A brushless motors. The motors run beautifully for 3 minutes. noone uses them nowadays for various reasons.

    Nicds need to be charged very carefully ( and discharged/stored, too) for good life and current. If not, they will die within a few charge cycles due to the 'memory' effect.
    It maybe Ok because it is cheap, but then, they become unreliable if care is not excercised.

    The NiMh cells are fairly excusing and tolerate incomplete charge, etc., dont have the Memory effect and live longer. They are better for the cost/performance. I suggest NiMh simply because, it is easy to charge.

    It is time you read a little more about Motors, Power sources , current draw and their proper usage, before you do anything else. It will prevent you from spending what you saved with the existing Motor !

    Elecrom is quite right: change the Motors!!
    docel
    ^Anything is possible..
    after YOU prove it!!

    http://bangalorerobotics.tripod.com

  5. #15
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    Default hiii

    so, for the last 3 days i am searching whole jaipur for those high torque low resistance stepper motors but hard luck...... so i am back to my steppers... my project submission date is near so i am trying whatever i can to make my mouse work.......

    first thing i did is to keep my mouse on dieting..... it has lost 350g in 1 day... how???? well i tried some unorthodox ways..... firtly i removed all those aluminium support for steppers -150g (used duct tape instead) ..... removed those readymade tyres -100g (used plastic bottle caps with electrical tape for grip) and also removed the castor wheel together with its wooden base -100g (used a simple round headed screw with thermacole).......

    now its working fine with power supply unmounted....... well thats enough for my formal project but not enough to satisfy me.... so i am looking for more improvements.......

    the first thing (nasty thing) which came in my mind was --- """"could i reduce the weight of steppers???""""" well once in mind, i had to try it. thanks to my friend for that spare stepper . i opened it up and after 5 hrs of investigation i figured out that the exta weight in stepper could only be removed if i get a sofisticated structure designed from lathe machine... but thats too much i could expect from my college....so i dropped that idea

    so i am back with tose 400g steppers.... now i started thinking of using other means to increase torque..... i figured out some ways but i dont think any of them is going to help me.... i am a little disagreed about them.........

    1) using gears : well this will give me more torque but at the same time make my mouse move like a snail..... its already running with 1cm/sec and i dont want to reduce the speed more....

    2) using pwm : well this is something new for me- "pwm with steppers"..... after all my thoughts i think its not a good idea... i am alredy running my stepper on 24v continous supply ( those whow are worried abt the health of my stepper--- its working fine without even getting warm even after 30 min .so i am sure its maximum supply voltage is at leat 24v)..... now according to theory pwm can only reduce the current if i keep voltage at 24v so torque can only ne reduced... yes it may help if i increase the voltage further but i am not thinking over it for now....

    now, i come to batteries.... well batteries can only be employed if my mouse can carry them.... they will weigh at least 500g..... now here comes my confusion.... one of my friend told me that ""even if i keep the voltage same then also more current will flow through batteries and so i will get more torque...."" ..... well i dont agree with him.. it is possible only if something in my circuit is limiting the current .... i am using a 12-0-12 transformer, half wave rectifier, 7824, and uln2803 for driving two steppers ( single power supply for both the steppers)....... i think everything here can handle upto 1A and uln upto 500mA per pin.... am i right????

    after writing above statement a new confusion came in my mind... i am using sequence 1100,0110...... for driving. so at every instance 4 pins of uln are active.... now coul it provide 500 - 500 mA on four pins at the same time ????

    another confusion: my calculations are
    voltage- 24v
    phase resistance- 75ohm
    so current per phase - 320mA
    if i am using above sequence will the single stepper draw double current??? i.e. 640mA for 1 stepper ,, means 1.28A for two steppers???? because if it is true my power supply cant give that much current and so i am not getting torque..... but at the same time i haven't burned any of my ics..... can u help me out????

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