Boe-Bot Navigation Question

hungryTechie

Hi all,

I have 2 questions related to Boe Bot Board of Education with Arduino.

1. Has anybody taught the curriculum available at learn.parallax for this robot? How long would approx take for a HS class that meets daily to complete chapters 1- 4? How about chapter 5?

2. The other question refers to the way Boe Bot moves. Why does one wheel need to rotate clockwise( right) and the other counterclockwise( left) to move forward? It seems odd to me, wouldn't be easier to move both wheels, forward, backward, etc? ( Lego has this, if I'm not mistaken) Is this similar to how the wheels turn in real world?

Thanks

Mike Green

Can't answer #1 for you. Hopefully someone else can. For #2 ... as a thought exercise, remove the two servos from the BoeBot and turn one so that they both face the same direction with the shafts pointing the same way and the cables coming out the same way. Look at them shaft-on and imagine them both moving first clockwise, then counter-clockwise. One direction corresponds to pulses shorter than 1ms and the other direction to pulses longer than 1ms. Now (in your mind's eye) install them back in the BoeBot chassis. One servo must move clockwise and the other must move counter-clockwise for the BoeBot to more forward and vice-versa for backwards. Lego probably has two wheels on the ends of an axle. When you look at the axle from one end, the wheel moves clockwise to go forward and, when you look from the other end, the wheel moves counter-clockwise ... it all depends on the point-of-view.

Duane Degn

hungryTechie wrote: »

2. The other question refers to the way Boe Bot moves. Why does one wheel need to rotate clockwise( right) and the other counterclockwise( left) to move forward? It seems odd to me, wouldn't be easier to move both wheels, forward, backward, etc? ( Lego has this, if I'm not mistaken) Is this similar to how the wheels turn in real world?

The motors on the BOE-Bot are continuous rotation (CR) servos. The user doesn't have access to the actual h-bridge inside the servo. With a h-bridge, one can just swap the power lines to the motors to reverse its direction. With a CR servo there's not an easy way to make one reversed (though it is possible). Since you don't have the option of reversing the direction of the motor with the wiring, you have to have the motor spin in the opposite direction by sending the appropriate pulses.

Sorry, I can't help with the first question.

erco

You can reverse the direction of a CR servo by opening it up and swapping the two DC motor wires. Simple for some, hard for others. Arguably easier to program for a beginner. But then you have a non-standard servo and your code won't work on a standard robot.

ValeT

hungryTechie wrote: »

Hi all,

I have 2 questions related to Boe Bot Board of Education with Arduino.

1. Has anybody taught the curriculum available at learn.parallax for this robot? How long would approx take for a HS class that meets daily to complete chapters 1- 4? How about chapter 5?

I taught a bunch of middle school students, and it took us the whole year to complete the kit including all of the projects. We met once a week for 1.25 hours.

Hope this helps,
ValeT

GordonMcComb

hungryTechie wrote: »

wouldn't be easier to move both wheels, forward, backward, etc?

Only if the motors were mounted to the chassis is the exact same way. But they're not. They're mounted opposite one another, like in a mirror. So, to go forward, one motor must turn in a mirror image to the other.

You're thinking motors like this, where you can mount the wheel on either side of the axle:

https://www.pololu.com/product/67