The wheels are working ... but the robot no :'(

[teazy]

Hi guys,
i have to make a robot for my informatic project, all the things are working (the motors run and the servo-motor too).
I've printed the wheels with a 3d printer, and i used an inner tube for the tires. I've made a python scrit.
When i run it and i lift the robot, the wheels turn normaly, but when i lay it on the floor, the robot doesn't move forward ... :/
What are the problems ?
I've listed 3 potentials problems :
- the tires
- the weight of the robot (too heavy ?)
- The motors are not powerful ? (i use two motors from here : https://www.amazon.fr/gp/product/B00JR6 ... UTF8&psc=1)
- the alimentation ? (i use 4 AA (1.5v each) for the two motors)

i join a picture of my robot:



ty for u help <3

[pfletch101]

You don't give us a great deal of information, but my guess is that the motors don't develop enough torque to get the car moving. A particular issue may be the large diameter of your driving wheels, since this will give the motors a further mechanical disadvantage (like using a lever backwards, with the long end under the load and manipulating the short end).

[teazy]

You don't give us a great deal of information, but my guess is that the motors don't develop enough torque to get the car moving. A particular issue may be the large diameter of your driving wheels, since this will give the motors a further mechanical disadvantage (like using a lever backwards, with the long end under the load and manipulating the short end).

So, a first solution is to decrease the diameter ?

[pfletch101]

So, a first solution is to decrease the diameter ?

That may not be enough. I see that the motors you are using are sold as being suitable for motorized toy cars, but I also note that their specified rotational speed (presumably unloaded) is 16000 rpm. This suggests to me that they are intended for use in drive systems that use (e.g.) a wormwheel and sprocket to produce a much lower rotational speed and (correspondingly) higher torque output to the driving wheels. You don't say whether there is any gearing between the motors and the wheels in your robot, and it doesn't look (from your image) as if there is. If I am correct, this is a much more basic problem

[MarkR]

I think you're likely to need a gearbox, or if you already have one, a higher ratio (i.e. slower speed and more torque).

The ubiquitous "N20" gear motors are tiny, can be cheap, and come with a variety of built-in gearboxes to suit many small robots. Either buy the "proper" polulu ones or cheap ones off ebay or from Chinese suppliers.

[OutoftheBOTS]

OK I will assume that you understand some basic physics.

The motor will output a certain amount of power.
Where power = force x distance(force is applied over), therefore force = power/distance
Most of these little motors will spin at about 6000rpm (yes that fast), then you multiply this rpm by the perimeter of the wheel you can understand the distance will be huge so if force=power/distance you can understand how you get very little force on the wheels.

Solution is gearing down will give much better force for the power level of the motor. When I build robot using these little motors I usually use a min gearing of 35:1 gearbox with a wheel size of 30mm radius.

You cam buy something like this with a gearbox and wheel ready for plug and play https://www.aliexpress.com/item/Mini-Sm ... autifyAB=0

[teazy]

Ty for the answers guys !
So i've to buy 2 gear motors ^^
these are ok
https://www.ebay.com/itm/Metal-Micro-Ge ... 3200068081 ?
(i hate the yellow motors xddd )

[Gavinmc42]

Adafruit have a blue metal geared version of those yellow ones
https://www.adafruit.com/product/3802

You have large diameter wheels so you need slower turning gearmotors that have more torque.

Not all of those 130 size hobby motors are the same, either.
https://product.mabuchi-motor.com/search.html?method=4

Typically motors of a higher voltage have more turns of thinner wire.
This means higher voltage, lower current and slower RPM.
The number mean wire size and number of turns,
11340 is 340 turns of 0.11mm wire, 2270 is 70turns of 0.22mm wire.
Lower voltage, high current motors are not as efficient as higher voltage lower current ones.

Typical robot wheel gearmotors are around 50-150RPM.

FC/FA/FF-130 = Carbon, metal, precious metal brush types.
FC- carbon are higher powers and don't wear out as much.
FA, metal brushes, cheaper for toys.
FF are higher performance normally used in equipment.

Those smaller metal gearmotors are using something like a FF-M20/N20.
Smaller size motor = smaller magnet = lower power output.

Power/Torque/RPM all dependant on what surface you are running the robot on.
Vinyl floor has lower drag than carpet, shag carpet you may need 4 wheel drive

Traction depends on your tyres, rubber bands work, silicone ones are better, then soft duro polyurethane.
Even foam wheels can be used on lightweight bots.

Those yellow gearmotors can be made better by swapping out the toy motor for a better one.
Motors are only about $1. but It is not unknown to rewind motors, slot car guys do it.

[alphanumeric]

This will be a rehash of what others have already said but it sounds like the motors are just stalling under load. If you pick it up, and run the motors so the wheels are spinning. How easy is it to stall the motor with your finger? If it stalls with very light finger pressure that's your issue. Your using the wrong motors and wheels for your situation.
I have two of these two wheel rover kits, https://www.adafruit.com/product/2939 I just test ran one yesterday. Drove around on my carpeted floor no problem. Pi Zero W with an Explorer pHat driving the motors. PowerBoost 1000c and 2200 MAH battery for 5V power. Keyboard controlled. The motors are geared in a micro servo shell, and mount easily to that chassis. Very happy with the looks etc.
My build pictures are here if you want to have a look. https://1drv.ms/f/s!AjOYwiwlwDtpgrNitzE9mWKSbll5jg
What are you using for motor control?