Help choosing correct gear motors & parts

Community General Discussions
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About me: I am a computer programmer as profession (I know C/C++, .NET, databases… etc.). As a hobby I do electronics, and I play with PIC microcontrollers (PIC16, PIC18, and lately PIC32)
Here is my first (and only) robot: youtube.com/watch?v=L3Dpe1v6G-w

I want to build a more advanced robot (for me anyways), basically I want it to be a computer (motherboard) on wheels (or laptop I’m still deciding). I have an M4-ATX to power the computer (if I don’t go for laptop).

My problem is I can’t find a chassis that would fit everything (motherboard, batteries, sensors (ultrasonic, laser distance finder), etc… later on I may add an arm), so I am thinking to make my own chassis.

Also, most of the chassis that I found on RobotShop or internet (that seem big enough) are extremely expensive. (Another reason to make my own)

I don’t know what motors & wheels to buy. The motors I want them with encoders, because I want to know exactly how much it moves.

I am thinking to get these motors (4 of them): Pololu 12V, 100:1 Gear Motor w / Encoder, but I don’t know if they are strong enough to carry everything.
I don’t need the robot to be fast, and it’s for indoor use.

I choose those motors for the price, encoder, and they seem to be strong enough? right?

I did not find a KIT for this motor, so I have to put it together myself :frowning:
I found this KIT: Parallax 7.2V Motor, Bracket and Wheel Kit, but it does not have encoders, and I’m not sure if the motors are strong enough?

To mount the motors I’ll need the Pololu 37D mm Metal Gearmotor Bracket.

Now the wheels I want them to look like this: BaneBots Wheel, 4-7 / 8" x 0.8", 1 / 2" Hex Mount, but it’s hard to figure out what wheels match for the motors I want to get.

What else do I need? How do I connect the wheels on the shaft of the motor?

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Thank you for your help!

For “RB-Ban-180 (0.75” hex mounting hub, 0.8" wide for 6mm shaft)" I did not see 0.8" wide, only 1 wide (or wider)?

About motor controller: what driver/controller do you suggest for the motor I choose RB-Pol-126 ? (I’m gonna be using a microcontroller between computer and motor driver)
Currently I am using L298N driver for my robot, but what I don’t like about this driver is that the drop voltage is very high. I am gonna be using 12V battery with a 12V motor, I cannot afford a high drop voltage. (Unless I put 2-12V batteries in series)
I might try to make a driver using MOSFETs… hmm…

Another thing that got me thinking is turning the robot. Most chassis I see on RobotShop (or web) is turning the robot by spinning the wheels at different speeds. But that causes a lot friction. I am guessing it is OK for light robots (or outside robots), but for something I want to make, isn’t it better to make the wheels turn left/right? (like a car) If “Yes”, then I think I will need servo motors powerful enough to do that. Any ideas?

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In order to determine of the motors will work, try the Drive Motor Sizing Tool. The one aspect it does not factor is is the coefficient of friction of the terrain - it looks like you have carpet, which is harder to roll over than a flat surface such as tile or wood.

Doing some rough estimates with the tool, four of those motors should not have any problem moving the robot on flat terrain. You would need two pairs of mounting brackets, as well as 4x RB-Ban-141 (4 7/8" diameter wheels, 0.8" wide with 0.75" hex bore), as well as 4x RB-Ban-180 (0.75" hex mounting hub, 0.8" wide for 6mm shaft).

To drive these four motor from a laptop or computer, you can either choose a serial motor controller (with the right specs of course), or add an intermediate microcontroller.

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You will find RB-Ban-180 at this link: robotshop.com/ProductInfo.aspx?pc=RB-Ban-180

It should be the appropriate hub for the wheel. Apologies for the bad link.

The voltage drop should not be too significant in the L298N at 12V and 2A. We do not believe it will affect too much the motor performance. The drop in voltage of the battery being discharged can be much more significant.

You can definitely do a rack and pinion steering system (like you would find in a car), instead of using skid steering. The torque you require will mainly depend on the mechanics you create. You can find very popular servos here: robotshop.com/hitec-servo-en.html
Skid steering is used in the vast majority of mobile robots - almost none use rack and pinion.

Also note that if you use a two-wheel driving system with caster wheels to support the weight, you will not have a friction issue.