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sushmair
04-07-2010, 11:47 AM
Hi,

Would anybody have any idea what is the torque of these motors? - http://onlinetps.com/shop/index.php?main_page=index&cPath=77_104.

I've asked the shop owner but not received a response yet (am in kind of a hurry) - was just wondering of someone around here has bought these and knows.

Alternatively, would any one know if these motors will work at ranged voltages - 6v to 12v? - http://thinklabs.in/shop/index.php?cPath=30_63&osCsid=80b3620fc1fe96dfea468f2423ba0714 . Again, have asked the shop owner but waiting for response and just checking here to see if folks know.

In both cases, will it make a difference to torque if voltage ranges from 6v to 12v while current is kept constant?

Rgds,
sushmair.

shashak
04-07-2010, 01:26 PM
wow ,
If you are in pune and in great hurry why dont you go for local shop (rajiv electronics or something).
These are not standard motors, even there manufatures will not be sure about there torque. Only relaible information about them are there rpm. Whats your requirement, means where you have to use them. As you must be knowing for high torque (load bearing joints) go with low rpm and for low torque (like wheels) go with high rpm. Its kind of emperical formula torque ~ 1/rpm.

vikas
04-07-2010, 02:22 PM
No one can tell you the torque for these ... Best is to buy and measure....

sushmair
04-07-2010, 04:19 PM
@shashak,

The robot will lug a maximum of upto 2 kg weight. Speed isnt very important (~0.5 ft / sec) . It will run off a differential drive thus 2 such motors are the req.

Rgds,
sushmair

allbits
04-07-2010, 06:44 PM
Just check the RPM of these motors. These motors normally use the same motor with a gearbox. The 200-300 rpm ones will hardly have 1-1.5 Kgcm torque, at normal cases and at 12V. Now, if you decrease the RPM, it meams more gears in the box, which means increase in torque. So a 10rpm box will have much more torque than the 200 rpm ones. But, 10 rpm ones will be terribly slow, i would suggest a 100 rpm one.

These motors will work at 6v, but at a reduced speed. DOnt forget to all .22 DISK CAP across the terminals. The motors are a bit bulky, which means you willneed a wheel with a bigger radius which will again make your robot b ulky. If you are on a budget,(I dont krnow if you are) buy a differential drive earth mover toy which will cost you Rs 250-350, hack it, and you will get a good set of motors with decent torque. But these will be good enough only for bots <1.5Kg.

sushmair
04-07-2010, 07:36 PM
@allbits,

Thanks! Your inputs are promising. The numbers that you give (200-300 rpm <--> 1-1.5 kgcm torque), can they generally be used as a reference for rough calculations?

Rgds,
sushmair.

pkshima
04-07-2010, 09:50 PM
A large dia wheel will reduce the torque and increase the speed.
Taking this into consideration I would go with a 30-45 rpm motor.

allbits
04-08-2010, 12:02 AM
@allbits,

Thanks! Your inputs are promising. The numbers that you give (200-300 rpm <--> 1-1.5 kgcm torque), can they generally be used as a reference for rough calculations?

Rgds,
sushmair.


No.

Dont calculate anything at all. That will simply waste your time. For small robots with components/motors without proper datasheet, its better not to calculate. Instead, make small prototype and SEE if they are working.

To calcuate the wheel diameter, battery type etc, you need the weights of these components before hand, which you do not. So it ends up with too many unknowns and few known parameters. You will end up in 'assuming' a lot of variables. So dont go for those calculations when it comes to small robots with less complications. Make a prototype with hard cardboard/3mm acrylic.

sushmair
04-08-2010, 12:47 PM
hmmm...thanks.

Just wanted your inputs on the battery that will be best for these kind of motors. I have a NiMH 9v battery (200 mAH). Will that be enough to drive two such motors or is ill-suited? Note that the microcontroller and motor driver will be driven from a separate battery.

Rgds,
sushmair.

akshay66
04-08-2010, 05:06 PM
i dont think a 9V 200Mah battery will be enough rather use it for circuits.

pkshima
04-08-2010, 05:46 PM
@akshay66 : Well 200Mah will definitly be more than sufficient actually. A 200mAH will not be :)

@sushmair : better go with a SLA battery. 2AH +.

akshay66
04-08-2010, 06:29 PM
I mean the same...

allbits
04-09-2010, 09:00 AM
1) you can use the normal 1.5V AA size battery (yes, the Rs 8.50 battery) if you are on a budget. connect 6 of them in series. People normally underestimate these batteries.
2) Use one of those Lithium batteries (you can browse for them at online shops) if you need to save space and weight. But then, your expense will rise up. You will have to buy the charger too.
3) You can use two AAA batteries for the microcontroller supply. Hope you are not using the good old 89c51.
4) Dont use alkaline batteries/9V batteries for motors which takes in more than a 50mA.
5) You can also use NiCd/NiMH batteries in series. They are real good, but since they are 1.2V a piece, will consume your space.

sushmair
04-09-2010, 12:25 PM
This is good info. Thanks all!

@allbits,

I have noticed that almost all RC toys use the standard AA size (1.2v) batteries in series. Technically, why do they score over, say 9v batteries?

Rgds,
sushmair

allbits
04-10-2010, 07:15 AM
Current.

These batteries can give more current per time. Motors needs current, so if your battery cant give much, they dont run.

9V batteries cannot deliver that amount of current. Yes, the battery chemistry is different.

if you need to know more about batteries, go through this.

http://batteryuniversity.com/partone.htm

sushmair
04-10-2010, 08:35 AM
Thanks allbits.

The site is really good - will help in buttressing my basics.

Rgds,
sushmair.

akshay66
04-10-2010, 12:25 PM
Really good website!!!