Sizing robot wheel motors

Hey! I was hoping to have some advice.

I am designing a small water pumping robot, that needs to be able to travel only backwards and forwards. The total weight will be about 1.5-2kg, and it will reduce as water is pumped. It will needs to travel about 6m in total, on a flat surface at fairly low speeds. Overall dimensions will approximately be length: 25-30cm, width: 15-20cm, height: 25-30cm.

At the moment, I am trying to determine what type of motor to use, and how to attach it to the chassis. Motors I am considering are TT geared motors (either plastic or metal) or a micro metal gear motor. Would the TT motors provide enough torque for the robot?

I also have a budget to remain within, so a lower cost option would be ideal.

Thank you so much

Motors I have looked at:

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You’ll probably want to look at larger motors than those. The micro motors especially are deceptively small. Any geared motor will do with a decent gearbox, but I’d suggest something with a worm drive - they’re high torque low speed, and they won’t backdrive - which means when the motor is off the wheel stays stopped so they double as a parking brake.

As a very rough rule of thumb, choose a motor with a torque rating in that’s about triple the weight of your vehicle in kg. You’ll need to do some reading/watch some YouTube videos on Torque and power (power = torque x rotation speed).

Once you know how much power you need you can choose a motor as power also = voltage x current.

Going straight will also be difficult without active steering. The easiest way to have it go fairly straight is to lock the drive wheels together with a single axle, rather than using separate motors for each wheel. Have a look at how gokarts drive and basically copy that.


Hi thank you so much,

There will be a small pin and guide track to keep the vehicle in a straight line. Do you have any suggestions of an exact motor I could buy, or how to narrow down the search?

Hi Hannah,

To add to Oliver’s post you can sacrifice some speed for torque by using some gears. There will be some power loss as you add more parts to the system but will allow you to use many more motors.

A good motor to start with would be this high-torque Kitronik motor (Core doesn’t have stock at the moment, but should have some between the 22nd of April to the 27th of April) it uses lots of power so you’ll need a that can supply the current to run it and something with enough capacity to keep your project running for long enough (A LiPo would be perfect here) and motor driver.
Some good motor drivers for the one above can be found here, I’m looking to see if the driver can handle a voltage input that the motor will run on (1.5 to 6V) and can pull the current through it (can draw up to 760mA, but we’ll say 1.5A so there is a factor of safety there)

Happy to help with anything else!

Hi thank you so much, really appreciate it!

It is a team project and my team mates have organised a PCB, Arduino and motor driver, so I think we have that sorted out. They have also ordered 18560 batteries and have said that up to 7v can be supplied, but it can be reduced.

Power can be provided to 2 or 4 wheels and we could incorporate active steering if it is easier, but it is not required. Using active steering, if we had 4 of the TT motors (either plastic or metal) would there be sufficient torque?

I am also bit confused about what a worm drive is, I have done some research but am struggling to understand. Can you buy motors with a worm drive attached to them, or is it a separate gearbox you need to buy?

With a motor like the high-torque Kitronik motor, could you directly attach it to a wheel and the chassis? Similar to how a TT motor attaches?

My knowledge it very limited as it is the first electronic project I have done :slight_smile:

The input spins really fast and the output goes really slow.

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Hey Hannah,

Sorry for the delayed follow-up, like Oliver mentioned above a worm drive is an arrangement of gears where a screw meshes with a gear.

We have a few options available to purchase that have both the motor and the worm gear in one unit, you can see a few of them here!

The Kitronik High Torque motor has a round rather than D-shaft, so it will be a little more difficult to attach to a wheel. The worm motors have a D shaft with an internal screw thread to attach shafts more easily.

Hope this helps!