Robot tranny.

[Builder1]

Hello All,
I'm trying to create a four wheeled robot and its going to need a relatively large motor, so I'm trying to have one motor do everything to cut down on weight and cost.  I'm wondering if I can use one motor to power the robot and change its gears to go forward or backward. Is that possible or should I have two separate motors, one for each task? If it is possible could you please send me a link to a site that shows how this is done? Thank you in advance for your response.

[paulstreats]

Just 1 motor would be a lot easier otherwise you are going to end up with 1 motor acting as an actuator and the other will be spinning but not powered up meaning that it will generate energy and obviously cause the driving motor to have to expel that extra enegy.

Basically you will just need a h-bridge to move it forwards and backwards and some gearing check the main site http://www.societyofrobots.com and you will find a guide to h-bridges there

You will find that the motor itself can spin either forwards or backwards so this solves your initial problem. The main part to worry about is getting the gear ratios corect so you have an effective compromise between speed and expected toque

[Soeren]

Hi,

I'm trying to create a four wheeled robot and its going to need a relatively large motor, so I'm trying to have one motor do everything to cut down on weight and cost.  I'm wondering if I can use one motor to power the robot and change its gears to go forward or backward.

So, how about steering?

If you need the same motor to do different tasks (beyond forward and back), you need eg. magnetic clutches, but I think you would be better off using separate motors for different tasks (and the clutches will be somewhat expensive, not exactly  lightweight and will make demands as to how everything goes together).

[Builder1]

Hello Everyone,
Thank you all for your inputs. If I decide to use two motors, one for steering and the other for powering the bot, how can I get them to communicate with one another. For example if the robot needs to make a turn, the powering motor would need to slow down so that the turning motor can safely make a turn. What I would like to know is how can I control multiple devices with a microcontroller. Thank you in advance for your response.

[JesseWelling]

Are you going for Tank Steer or Car Steer?

[Cotowar]

Have you thought about going with two smaller motors to power the left and right sides separately? This would give you zero turn capability, and would also allow you forward and backward movement. You could place them in the center of the chassis to keep the balance the same, and place the electronics and power source at the front or back.

You'll probably end up using at least 2 motors anyways, seeing as one would drive the wheels, and the other would turn them. I suppose you could build the rear wheel turning thing that some pickup trucks come with now. That would be pretty sweet.

Hope that helps.

[airman00]

you need a dual motor speed controller and a joystick to control it . Most speed controllers have inputs for R/C , so just hack a joytstick to give out those outputs like by servos and you;re set.

[Admin]

I always tell people their first robot should always be differential drive (two motors, one for each wheel, and a caster):

http://www.societyofrobots.com/programming_differentialdrive.shtml

You don't want to deal with complicated gearing or clutches or complex control algorithms, trust me!