Help with motor wheels and torque

Help & Support Robot Parts
1

Hi. I’m building a robot lawn mower with 1blade. Two motor wheels on back, and two casters at front.

I bought 2x motors for wheels, which is good on flat surface, but not enough strong to run mower on the grass.
My motors are: 2x High torque motors 6v, 90RPM. They are connected to H-Bridge. I tried to connect to double voltage (12v) and still not enough torque.

I saw in video where someone uses similar motors, but stronger-12v 25RPM. He couldn’t
run at 3x lion batteries (12v), then he used double voltage (16-24v, which risk overload his motors) which show good to run on grass.

If we look manufacturer specification Table for my motors, he used "5.2"kg Torque on his motors 12v, and mine are Torque only "0.9"kg! That is big difference.
I didn’t mean that my motors will be that weak when bought them.

For that type of motor I will need 12v 25-30RPM, but that will be maybe to slow.

So, I am here to someone help me which motors for wheels (19cm) you recommend me for buy? It will be good 12v and cheaper.
Thanks.

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2

Blockquote
So, I am here to someone help me which motors for wheels (19cm) you recommend me for buy? It will be good 12v and cheaper.

Nobody?

3

Hello @Smurf2 and welcome to the RobotShop community,

My motors are: 2x High torque motors 6v, 90RPM. They are connected to H-Bridge. I tried to connect to double voltage (12v) and still not enough torque.

It is not recommended to use a higher voltage than the nominal as it will reduce the useful life of the motors. Also, if you increase the voltage you will get a higher speed, but not necessarily a considerable increase in torque. If you need higher torque you should add a gear reduction (or look for a different model with a higher gear down ratio).

To calculate the torque that the motors will need you can use this tool:

Once you know the approx torque you’ll need you can check this comparison list to find the right motor:
https://www.robotshop.com/en/compare-dc-motors.html

Also, as this robot is meant to be run on grass/mud you should also take into account the type of wheel:

I hope this helps!

Let me know if you need further assistance

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Thank you.

Yes, I am aware of that. I don’t want to if I don’t must do it. Can be another model too.

For now mower have 4kg. There are printed plastic wheel 19cm, which all calculated is 2.07 Nm of torque.
But don’t know how many batteries in future I will use and its weight, also how much printed enclosure will be weight.
So, think will be good motor from 2 to 4 Nm Torque, in worst case 5Nm.

Not sure how much rpm need, think around 30-50rpm, I will test that soon. Can you please give me some examples which motors can be good?

Can be bigger RPM and then set it to like 50%? That not give enough power, guess?

5

For high torque and low RPM the best option is a geared motor, you can find some good options in the Gear Motors section of the store.

Can be bigger RPM and then set it to like 50%?

RPM can easily be reduced with PWM.

Some options that could work for you are:

6

Thank you very much.