Ok tiny updates for this project design. I ordered and chose a entry level high torque Nema 23 motor for testing. It draws 2 amps per coil with 2 coils. So that's 4 amp total. Voltage range from 3.6v to 45 volts. Case size is standard 57mm x 57mm for NEMA 23 and 76mm long for the largest case. Take in mind there are 125 oz -250 oz in versions that are only 58mm long but they draw more current to get that torque from a smaller coil. I will write a expert of motor choices and why I'm going with steppers as a standard.

Now that I have the motors modeled I can use these as reference to design the motor pods and the chassis. Since the rover is 6 wheel drive I am using 6 individual high torque motors. Gearing us available for the Nema 23 motors but with these torque ratings it won't be needed.

This is what they are modeled after and I have them in the mail to arrive in a couple days. These steppers are from pololu but thanks to industrial standards you can buy these motors just about anywhere and I have seen them as low as 20 dollars but you have to wait on China shipping.

Good morning EZ Robot Community!

Today I wanted to post a tiny bit about steppers, how they are controlled and you shouldn't be afraid to use them. One of my biggest concern about entry level and midrange robotics is the heavy reliance on plastic gearboxes and in some cases brass gear boxes. They are typically very loud , and unreliable once you start adding batteries and equipment to your robot. Stepper motors however are brushless high torque motors that don't need a gearbox. They have torque ratings in the thousands of ounce inches. The also come in sizes as small as 40mm X 40mm Nema 17 for a small robot and 57mm x 76 Nema 23 for larger robots. They operate on pulses from your EZB but not pwm. The speed the stepper moves will depending out how often a pulse is sent to the motor and it will move 1.8 degrees for every pulse applied either forward or reverse.

So why a stepper?

• High torque motors :starting at 125 ounce in on a Nema 23 , we are testing with a 190 ounce inch @3.6 volts. Don't be fooled by the ratings though. It is common for steppers to be ran ten times higher than that and the torque curve rises with voltage. For testing purposes I will use a Texas Instruments 2.5a stepper controller that can handle up to 45 volts. We are shooting for 12 volts which is still 4 times the original torque rating.

• industrial standard ratings and casings make buying a motor to fit easier and replacements when needed.

• steppers are rebuildable. The coil can be rewound if ever damaged by over heating. Try doing that with a 100 dollar wheelchair motor! (Possible but not made to disassemble)

-Accuracy : by default each full step is 1.8 degrees but in a sudden need for more accuracy a simple (digital pin on) can trigger micro stepping up to 1/32 of a step. ( that is about 1/16th a degree).

-Reliable control: because of the previous mentioned control on rotation if you wanted for example to tell your robot to move forward 1 foot, you could do so will great accuracy. This would not change with the grade of the surface. Let's say you wanted you robot to turn left or right, 15 , 30, 45, or even 90 degrees then it could do so with accuracy as long as the detent torque limit is not exceeded. (Aka as long as all the motors do not stall from getting stuck the turns are accurate)

Here is lots of technical info but what is important to know is with a simple script, time designation a microcontroller ( like ezb) can control this with the aid of a stepper driver.

http://en.m.wikipedia.org/wiki/Stepper_motor

The l298n is a basic stepper controller but it takes one l298n to drive a single stepper because they have two seperate coils inside. L298n does not have micro stepping capabilities, feedback for stalling or limitation of the current. A BVR8825 Texas Instruments driver is a cheap and effective choice.

Here is a forum explaining the use of l298n and other controllers for steppers. For those who want a more sophisticated controller I will make one available when the base is released.

https://forum.allaboutcircuits.com/showthread.php?t=37626

One of the goals of this design is to make a complete rover as well as just a rover base that can enter a doorway , pass through and if it needs to turn around it can do a zero radius turn and exit the doorway smoothly. The wheels turning helps but the robot cannot be too long or wide either. The type doors are 30 inches but because of the edge of the door and hinge that is realistically a 28 inch opening. This is the target space we are working through.

Thanks Josh for the stepper overview! My question is why aren't they used more often? I would presume because they require more support boards ie stepper controller and digital output pins which all add extra cost.

They aren't used as often because they are more complex. Instead of applying power through two wires and you go, you need a microcontroller driver to send pulses to them. They use to be really high priced but thanks to DIY community with 3d printing and cnc machine projects the market for competitive stepper motor prices has emerged. Mostly I believe it is the intimidation to the customer that he or she won't figure out what to do with them. Thanks to newer and easier to use drivers and software for ezb this kind of quality in a home made robot is easier to obtain.

wanna see how much more accurate steppers are for a drive system? this is 1/2 step accuracy , but motor controllers im looking at are 1/32 microstep accuracy. At 1/2 step accuracy this little dude runs for 10 minutes in a predefined square before a wheel catches a edge of the table.

https://www.youtube.com/watch?v=831qjVX6YLA