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prashu20
07-27-2010, 12:37 AM
i connected motors with output pins of l293d under no load they run pretty well but when i placed chassis over ground they stopped running .when i connect to battery directly they run pretty well under load and no load what can be the possible problems with my connections to l293d,outut voltage is 12v and current is 52 ma :).also give schematics of connections of l293d
thanks
cheers
prashant

vikas
07-27-2010, 02:34 AM
which battery are you using ( current and voltage specs please ) , torque of motors , weight of chassie ... maybe then we can help .

yaniv
07-27-2010, 04:25 AM
I've connected 2 geared DC motors to l293d, both the motors run at a higher speed clockwise compared to anticlockwise infact speed at clockwise is double that of during anticlockwise rotation(so is the applied voltage across the motors) Is this Normal??

prashu20
07-27-2010, 06:05 PM
i m using normal 9v hw alkaline batteries ,motors are 100rpm 12v ,dont know the exact weight of chassis ,could u please tell what can be the possible problems

lolman_returns
07-27-2010, 06:12 PM
Does the L293D heat up when you fix the chassis?

vikas
07-27-2010, 06:42 PM
9v hw alkaline batteriesThe will not work , not enough current for anything other than running simple circuits. change to high amp batteries.

prashu20
07-28-2010, 11:37 PM
no l293d doesnt heat up when conected to chassis .i dont think weight of chassis is a issue as when i connect my chassis directly to 9v battery the motors run pretty well under load and no load ,i think current or circuit connections are the main problem i am posting my motor driver ckt diagram ,as sensor module is working fine so im not posting it down here ,hope now u can point the problem
cheers
prashant

lolman_returns
07-29-2010, 12:53 AM
Just remember, the L293D can only provide a max output current of 1A, try running one motor at a time and see if there is a difference. Running two motors simultaneously with even the wheels attached on the ground = friction + weight of the chassis + bend in the axle = a lot of current for un-geared taperecorder motors

allbits
07-29-2010, 03:07 AM
Vikas have already given you the solution.. change your batteries.. you are using 9V PP3 batteries, and it WILL NOT work.
Use NIcd, NIMh, or LI chemistries. Read Datasheet of L293D... L293D will drop Voltage.

L293D will give you 600mA max while L293 will give you 1A max. Read the datasheet for the specific manufacturer. Changing your battery chemistry will solve your problem. But, if you expect the community to help you, you should mention about the specs of your motor, or any other component that you have in your circuit. Post your circuit !! or else, the solutions you get might not be the best, if not wrong.

vikas
07-29-2010, 10:07 AM
Switch batteries ... Also i think u are using tape recorder motors , some of them run at different spends according to polarity.

POST A PIC OF YOUR ROBOT ... a picture is worth a thousand words.

docel
07-30-2010, 12:51 AM
Pin 8 is connected to 7805. It wont work because the motor O/P will be around 6v.
Connect Pin 8 of L293D to 9v directly.
If you really want to use 9v batter, then use 2 in parallel. Or use 8 1.5v cells in series ( 8x1.5v=12V= Rs.80/-)

Study this internal schematic of the LM393 carefully.

259

The O/p transistor is open collector. This means it needs an external Load Resistor.

prashu20
07-30-2010, 10:15 PM
i saw similar robot with my seniors they used same 9v batteries ,and robot worked very well ,as mentioned by u that l293d gives max 600ma current but iam getting only 52 ma .i have posted my motor driver ckt in earlier post ,please see ckt and then post comments on wrong connections if any

prashu20
07-30-2010, 10:21 PM
i have connected pin 8 to 12 v directly ,please see ckt

docel
07-31-2010, 08:28 AM
Prashu,
We have made more than 10,000 of these with the same circuit and all of them work pretty well. I dont see any reason why it should not work or is not working with you. it only means that you have made some fundamental mistake that you are not aware of or have failed to tell us.
These work with 9v alright, but not for more than 15-20 min. beyond which the voltage and current output drops. You can see it if you connect a DMM to the battery and monitor the voltage when the motors are switched on. Besides, the 9v battery cannot provide the start-up current drive necessary for the motors. This may be superfluous as I see youre using a 12v battery as the motors Vcc.

Use the 9v battery ONLY after the robot and the sensors work positively with an external 12v supply.
Just because someone made it work doesn't mean you can too, since there is no way you can mimic someone else's working conditions 100 % as is. Most people cant solder properly and that leads to bizzare problems that is quite difficult to pin point, as a beginner. You'll be surprised how many people make stupid mistakes regarding voltage, current, and Motor drives till they realise that mistake. :) You have made a similar 'stupid mistake' regarding the Op-amp and ground connections.
One cannot make electronics work without measuring anything, so use the DMM and see whats happening at every point. A beginner should NOT use dual batteries unless they know and understand basics regarding potential difference, grounding principles and battery connections.

So, why dont you post some pics of your handiwork? Everyone has a mobile phone with camera nowadays. ?Beg borrow or steal a camera-phone and post some pics. IF you are serious that is.