10K would be fine!, it's not at all critical.

They perform the same as the top 10K's, as Ron H says.

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This is mainly because my battery is 12V. I dont think there is any point using a 24V motor when my supply can only provide up to 12V unless im mistaken
So can motors be placed parallel to each other?

 

Yes they can, but it seems really pointless designing something that way?.

You don't need a 24V motor, just a larger 12V one!.

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I cant seem to find any large 12V motors. Most of them are in standard size. meaning its rather small. and the battery weight is quite heavy for a single 12V motor to support.

Nigel, when u said it was pointless, what do u mean by that? wouldnt the torque increase by doing that

 

As a modification, after design, there might be some point to it - but from the initial design stage you should be looking to design it properly - not design it from scratch with fairly dodgy twin motors.

Also, two small motors will probably cost more than one decent one, it's not a good design idea!.

There are a great many sizes of small electric motors available, how big are we talking about?.

Oh - one quick thought! - assuming this is a four wheeled vehicle?, using a seperate motor feeding each wheel would be a reasonable design choice.

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exactly, thats what i suggested. and connecting two motors might give you more mechanical losses. you will have to couple two motors on a single shaft. that would be a problem!!!!

ive seen alot of BIG 12V motors with gearboxes and they have alot of torque! so i would say that you should find a big 12V motor.

 

i will be making a four wheel vehicle. one 6V motor(approximately as it was taken from another r/c) to control the left right motion for the 2 front wheels, 1 motor for the left rear wheel and 1 motor for the right rear wheel. I have actually already bought the 2 12VDC motors since they were selling quite cheap.
I dont plan on using 2 motors on 1 shaft. 1 motor for 1 wheel. Of course other than the mechanical losses issue, i am also abit worried on the motor alignment. This would mean 1 motor could be slightly faster than the other one. But both motors i bought are the same type, so i suppose it shouldnt be a problem.
Oh forgot to mention the motor size, i cant exactly give the precise size but its slightly larger than the size of a thumb.
So should i go ahead with my plan of connecting it paralelly or buy a large 12V motor. But buying a large 12V motor or motor with gears at my place could go up to around 100 bucks.

 

i have no experience in building robots and R/C cars but i think that if you use 4 small motors for each wheel then the steering will be more accurate. the type of steering you are trying to use is used in cars. but when all four wheels have a motor you will have to use a different type of steering mechanism simillar to a tank. and by using 4 motors you wouldnt need to have big motors at all. but ofcourse that depends on the load that the motors have to drag.

just my 2 cents !!!!!!!!!!!

 

yup i was thiking about that. But the Hbridge is still the problem. placing motors parallel to each other isnt really effiecient. but i guess i dont have much choice

 

so, the problem you are now facing is that PICs dont have more than 3 PWM modules. while you want 4 PWM modules in one PIC. well then how about using two hardware PWMs and two software PWMs. i think that will solve the problem

 

wow...i never thought about it. but just writing the program for the builtin hardware is already complicated. but i'll give it a try. thx for the suggestion!

 

Someone mentioned the 16F684 the other day, the datasheet says it's got four PWM channels - I should have a look at it!.

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PIC programmer software, and PIC Tutorials at:
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Oh, i seem to have tforgotten to mention one more thing. If i continue end up building another hbridge for my 2nd motor, it would COST me alot of money.
The problem is in my country here(malaysia), mosfets are hard to get in regular electronics shop and have to be ordered thorugh certain companies. The international rectifier mosfets they are selling cost 10 bucks each. I seriously find it ridiculous to spend 80 bucks on 8 mosfets. So, instead of using mosfets for as my transistors, i plan to use darlington pair(cost around 3 bucks or less each)
After reading through the datasheets, they dont mention anything about the switching frequency.
Does anyone have any experience dealing with the darlington pair? are they capable of 1000 hz pwm switching? but there are websites that use them. im really unsure whether to use them. The diagram below is an example of it. dont remember where i got it though

Attached Images

tip120.jpg (18.0 KB, 145 views)

 

i have been seeing the 16F684 in the featured products list at the microchip website for quite some time. its really an impressive device. 8 channels of 10-bit A/D, two comparators, 4-ch PWM 10-bit, internal oscillator, 12 I/O pins in a 14-pin package.

i dont know about the switching characteristics of darlingtons as compared to MOSFETs but i do know that darlingtons are used in H-Bridge circuits with PWM. go to the page http://www.bobblick.com/techref/proj...e/hbridge.html for more details. the circuit uses the TIP120 and TIP125 darlington transistors which are commonly found everywhere.

one thing that i would like to point out is that Nigel's PWM tutorial uses two PWM channels. you could also use two PWM channels for two motors. one motor will drive the two wheels on the left and the other will drive the two wheels on the right by two drive belts. that way you wont need to have 4 motors. but that would be possible provided that the motors are capable of dragging the load. now thats up to you to experiment with

 

It seems that the 16F684 is made specifically for A/D conversions and PWM functions seeing the number of I/o it has. But unfortunately, i just bought a 16F876 seeing it has most of the features i require. 8)

I dont really get Nigel tutorial on the PWM though. How isit possible that 2 PWM channels are capable to control forward and reverse of 2 motor. I better ask him this in his support forum