Choosing DC motors for soccer robot

[JochemP]

Hi,

For a school assignment I am building a football/soccer (which one do you prefer? ) robot. It's built in a circle with 3 motors with omnidirectional wheels attached. It's probably going to weigh 1,5 kilograms and needs to run at about 1 m/s.

At first I bought some DC motors but the RPM was too high and the power too low, so when I lifted the robot the wheels tilted like mad, but when I put it down on a flat surface the motors blocked and stopped running.

So a bit of researched learned me I failed buying the correct motors, so now I need to spend money again on some proper motors. However, I am afraid that I will buy the wrong ones again, so which ones can you recommend. Will continuous rotation servos do the job, and if not, can you give me some recommendations?

Thanks a lot beforehand,

Jochem (The Netherlands)

[futurrobotech]

No matter what DC motors you get you are going to need some type of gearing system or it WONT run

[TrickyNekro]

You can keep the motors... But you will need some gears to build up some torque and have some more controllable speed at the wheels...

Which motors did you bough... Probably someone here would know what gearbox should fit ;-)

[JochemP]

I bought those ones, I do not have a type number or something...

http://t.co/BwbKoHR

Translated it says:

DC Motor made by Johnson with a continuous wave.
Technical data: operates from 1,5V to 12V
With 12V rpm is approximately 18.000 rpm
Dimensions (length x diameter) 60x37 mm
Contains two sticking out axes, one on both side.
Dimensions of axes (length x diameter) 9x3,2 mm and 14x3,2mm

If someone can recommend me a gearing system I can use, I would be very grateful 

[DJSprocket]

Do you have any information on the "sticking out axles" such as the diameter and if it has a flat sot for a set screw. that would be the more important information for picking a gearbox other than the RPM output and the desired RPM and torque...

[Jak24]

HI,

Is this project for Robocup? (i am assuming because the specs are very much alike)
or is it just for a school competition?
and also it's better if you by motors that come with a built in gearbox as it is much easier
then searching for a separate gearbox,
pololu has some reasonably cheap motors and some gearboxes
http://www.pololu.com/catalog/category/22
and it would be helpful if you told us what kind of omniwheels are you planing to use (what diameter)
then maybe we could suggest a suitable motor/ gearbox with witch you could achieve 1 m/s

Regards
Jak24

[Soeren]

Do you have any information on the "sticking out axles" such as the diameter and if it has a flat sot for a set screw. that would be the more important information for picking a gearbox other than the RPM output and the desired RPM and torque...

You don't like to read? 

Dimensions of axes (length x diameter) 9x3,2 mm and 14x3,2mm

And from the photo on the linked page, it sure seems like it has a D-groove.

[Soeren]

Hi,

operates from 1,5V to 12V
With 12V rpm is approximately 18.000 rpm
[...]
If someone can recommend me a gearing system I can use, I would be very grateful 

Depending on your wheel size, total weigth, wanted speed, drive voltage etc. you'll probably need a gear reduction of say 50 to 150 and that can be accomplished in one or two sets of sprockets or a single worm gear.
First you need a small metal sprocket for the motor and a large sprocket for the wheel axle. If you need a larger reduction, you need a separate "blind" axle with a set of sprockets too.

With a worm drive, you need the worm to go on the motor and a worm wheel with the number of sprockets that you need it to reduce for the wheel axle.
You might consider a timing belt power transfer to keep the gears off the wheel axle and that could be chosen for a (minor) reduction as well.

[JochemP]

I am horrible at mechanics and constructing things with gears and stuff, so I am willing to buy new motors for about €15 per motor.
I am indeed planning to participate at the Dutch Championships Robocup playing 1vs1 soccer

I am using the following omniwheels with a diameter of 50mm:



For the rpm needed:

I measured the diameter of the wheel which is 5 cm, so the perimeter is about 16cm (hard to tell exactly as the wheel is not perfectly round). So when needing it to run at 100cm per second, it needs to run 100/16 a bit more than 6 rps, which makes a desired rpm of approximately 375 rpm. Which gear motors correspond with these needs? 

[JochemP]

I almost made my decision, I made a list of 3 motors which I think will do the job. I adjusted my needs a little bit, I think 0,5 m/s will be sufficient.

So my list contains these three:

http://shop.conrad-uk.com/hobbies/modelling/modelling-engines/modelling-gears/model-built-driving-engines/227552.html

http://shop.conrad-uk.com/hobbies/modelling/modelling-engines/modelling-gears/model-built-driving-engines/227544.html

So these two are the same except for the gear ratio, and for the last one:

http://bit.ly/hJeBSn

This one is a tad more expensive and also has a gear ratio of 1:30.

Which one do you recommend?

Thanks a lot for your help!!! 

[Jak24]

HI !

I am horrible at mechanics and constructing things with gears and stuff, so I am willing to buy new motors for about €15 per motor.
I am indeed planning to participate at the Dutch Championships Robocup playing 1vs1 soccer

I am using the following omniwheels with a diameter of 50mm:

OK first of all that omniwheel has a diameter of 40 mm not 50, acroname makes them :
http://www.acroname.com/robotics/parts/R77-4CM-ROLLER-3.html
Also you may not want to go with that omni wheel as it has nylon rollers and they don't have much grip compared
to the one with rubber rollers http://www.acroname.com/robotics/parts/R98-4CM-POLY-ROLLER-3.html
and another thing, i wouldn't recommend choosing this omniwheel as it was a rather small diameter, and
also the one with rubber rollers is quite expensive(almost 50$), and i have personal experience with them and i can tell you they are quite hard to mount them on to any motor,
what i would recommend is getting these omniwheels:
http://store.kornylak.com/ProductDetails.asp?ProductCode=FXA308
or this one
http://store.kornylak.com/ProductDetails.asp?ProductCode=FXA309
which are cheaper, have a bigger diameter, have rubber rollers, and can be mounted more easily.
In the tutorial for the omniwheeled robot:
http://www.societyofrobots.com/robot_omni_wheel.shtml
you can see that admin mounted these wheels using a servo horn to mount them on servos, maybe you could use a similar idea to
mount your wheels on the motor.

For the rpm needed:

I measured the diameter of the wheel which is 5 cm, so the perimeter is about 16cm (hard to tell exactly as the wheel is not perfectly round). So when needing it to run at 100cm per second, it needs to run 100/16 a bit more than 6 rps, which makes a desired rpm of approximately 375 rpm. Which gear motors correspond with these needs? 

you might want to re-do the calculations with the info i gave you

I almost made my decision, I made a list of 3 motors which I think will do the job. I adjusted my needs a little bit, I think 0,5 m/s will be sufficient.

So my list contains these three:

http://shop.conrad-uk.com/hobbies/modelling/modelling-engines/modelling-gears/model-built-driving-engines/227552.html

http://shop.conrad-uk.com/hobbies/modelling/modelling-engines/modelling-gears/model-built-driving-engines/227544.html

So these two are the same except for the gear ratio, and for the last one:

http://bit.ly/hJeBSn

This one is a tad more expensive and also has a gear ratio of 1:30.

Which one do you recommend?

Thanks a lot for your help!!! 

i have personal experience with the 3rd motor , it's terrible, DON'T use it.
The other 2 look OK, i would recommend using the 30:1, also i saw at the bottom of the link that they sell a mounting for it.
but also that motor looks quite heavy,(it doesn't say a weight but i am assuming from the size)
and if you want to keep your robot under 1.5 kg then you have to take in consideration things like this.

Regards
Jak24

[pmckinnon]

Hi guys,
you might like to check out www.rotacaster.com.au for an omni-directional wheel.  They have a polyurethane roller but have some softer ones again coming in the next month or so.