needed recommendation for motors

[superchiku]

hey guys ,how are u all ,recently i got an idea of making a very fast and efficient line tracer , the only problem is that i dont know what kinda motor and motor controller to use to make such a fast robot , i can take care of the electronics and programming but i need to know how to make a efficient and fast line tracer and what kinda motors to use for that , should it be high at torque or rpm....any recommendations??

[Pratheek]

DC motors will be the best option for a line follower. The ratings will depend on the characteristics of your robot(weight, wheel radius, etc)

[superchiku]

i want it small and fast

so any recommendations>

[bens]

We have a large variety of high-quality metal gear motors that you can browse here:

http://www.pololu.com/search/compare/51

The 30:1 micro metal gearmotors are used in our 3pi robot and give it a full speed of around 1 m/s (the 3pi supplies 9.25 V to the motors).  You can see a video of the 3pi following a line on the 3pi product page, so you can get a feel for what kinds of speeds you can get out of these motors.  Each micro metal gearmotor has a high-power (HP) version that draws more current but is faster and stronger in turn.  The comparison table should let you pick the motor that has the torque, speed, and current-draw characteristics you're looking for.

I'd need to know more details about your robot and how you plan to power and drive your motors in order to make an accurate recommencation, but based solely on your "small and fast" criteria I'd suggest one of the following (all specs at 6 V):

10:1 micro metal gearmotor HP: 6000 free-run RPM, 4 oz-in stall torque, 1.6 A stall current
30:1 micro metal gearmotor HP: 1000 free-run RPM, 8 oz-in stall torque, 1.6 A stall current
50:1 micro metal gearmotor HP: 630 free-run RPM, 15 oz-in stall torque, 1.6 A stall current
30:1 micro metal gearmotor: 440 free-run RPM, 4 oz-in stall torque, 360 mA stall current

- Ben

[Trumpkin]

hey bens, do you work for pololu?

[bens]

Yes, I do.

[ArcMan]

I've been in several robot racing contests where fast, powerful and small are important.  Without fail, the winner always used R/C car motors powered by the standard 7.2V sub-C battery packs.  Check out hobby stores for these motors.  There are many online and maybe 1 or 2 local to you too.  Depending on how many turns the motor armature has, they can draw anywhere from 5A to 30A, so a powerful drive will be needed.  You can use a standard R/C car drive, too.  The drawback is that you will have to build your own gear train, which is what we do for the racing robots.

[bens]

In my experience, when it comes to autonomous line-following robots, the limiting factor is rarely the speed of the motors.  Very quickly you get to a situation where you simply drive too fast to hold the line around the curves, lose the line, and fail.

[superchiku]

i see the recommendations u have given but 1.6 a stall current is a little too high coz a l293d wont be able to handle such high current , so i guess some kinda fast and efficient motor which draws under 1 A of current and can be driven by 12v,6v whatever may be ....

[bens]

Then I'd suggest you go with the non-HP versions, either 30:1 or 10:1.  If your robot is light enough, the 10:1 should still provide enough torque.  If not, the 30:1 at 12 V will probably give you more speed than your code can easily handle if your course has tight turns.  Or you could consider using a slightly beefier motor driver.

- Ben

[superchiku]

ya the l298 will be a better motor driver , i have implemented some logic which will make it go faster only if it senses a straight path for a long time and plzz explain what do u mean by 10:1 and 30:1 , is it some kind of torque to something ratio...

[bens]

Those values are the gear ratios.  For example, a 10:1 gearbox means that the gearbox output shaft makes one full rotation for every 10 full rotations of the motor's shaft.  The gearing between the motor shaft and the gearbox output shaft allows the unit to generate more torque at the cost of rotational speed.  Higher gear ratios produce slower rotation, but higher torque.  You are looking for the ratio that offers the optimal blend of speed and torque for your particular application.

As far as your logic about going faster if it senses a straight path for a long time: on paper this sounds like a good idea, but in practice it will probably get you in trouble.  Imagine a long straight-away that ends in a sharp turn.  Your robot will accelerate to high speeds on the straight section, but then it will probably be going too fast to make the turn when it finally reaches it.  At any rate, good luck with your line follower!

- Ben

[superchiku]

well then ill go with ur recommendations as far as the logic ,ill have on board encoders and some other logic which i have designed which will limit the speed and help me turn,any place from where i can buy these motors and yes the robot is small and compact