I’m Building an autonomous mobile robot using differential drive and have a few questions. I’m using two continous rotation modified Hitec 422 servo motors, a Basic Stamp II (education board), two Dubro 2.75 in. wheels, and a NARP 4cm omni direction wheel.

1) If I’m using two HS 422 servo motors and a Basic Stamp II do I need an H-bridge. I was planning on connecting my servo motors to an L293 chip then connecting the L293 to a Basic Stamp, but a classmate told me I didn’t need one, I could connect the servos straight to the Basic Stamp. Please Help!

2) If I need to connect my servos to an H-bridge do I actually open my modified servos and connect the two pins of the motor to the H-bridge.

3) I read a regular caster is a very great ideal for the third wheel, does anyone know a good way to mount an omni directional wheel to an aluminum chassis.

ANY HELP WOULD BE APPRECIATED

 

You do not need any drivers if you use servo motor. From stamp you can send special comand pulsuot for control servo.
You need only additonal power s. for servo.Do not use +5V from controller

 

Is this true for servos that have been modified for continous rotation using
a basic stamp II.

 

Yes. The only difference is that the variable resistor inside has been replaced with fixed resistors. (See your other identical thread).

 

And you just connect the pulse width modulation pin from the servo to the
Basic Stamp II.

 

Yes, at the exact correct pulse width the motor won't turn, below that it turns one way, and above it the other way. As you mention you're using the education board, isn't it all explained in the documentation included with that?.

__________________
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http://www.winpicprog.co.uk

 

I haven't bought the Basic Stamp II yet I have been doing some research before I do. So I would connect the servos to the spot on the board of education for connecting servo's(I saw an exampe in the What's a Microcontroller? book ). Also do I use an external 5 volts for the servos. I read somewhere its not recommended to use the regulated 5 volts from the board.

 

Yes, use an external supply for the servos - two of them will take more power than a 7805 can supply - in fact one might well take more power than a 7805 can supply!.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

So could I drive both motors from the same 5 volt 7805 supply. Or will I have to have two 7805 supllies and connect a servo to each.

 

So I could use a 3 pin male/male header connect my power pin to a 7805 5 volt supply, connect my ground pin to the vss terminal and connect my last pin to a pin on the basic stamp.

 

Yes, except that it is better to not use the power coming from the PIC electronics' voltage regulator to power your servo. It will increase chances of the servo noise disrupting your PIC's operation and chances are the servo draws more current than the logic voltage regulator can supply. Just attach it directly to the main battery (assuming it's voltage is within servo specs) or use a separate battery.

 

The BIG advantage of using a seperate supply is that it really seperates the motor noise from the electronics - it was common practice to do so in radio control models, although more recently they have started running the electronics off the main drive batteries through a regulator.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

Yeah thats what I meant I can use a seperate supply from a 7805 supply.Then I would connect the servos ground pins to the vss terminal on the board of education. Then connect the last pins to a basic stamp output.

Also would it be posible to power the board using four 1.5 volt
batteries, then connect both servos to the servo headers on the
board. Or would this add between the electronic and motor noise.

Which idea do you think is better.

 

You can power your logic and servos from the same battery or different batteries. Just don't power your servos from the same regulator- connect your other electronics to the regulator and connect your servos straight to the battery (if it is 5-7V). If your battery is higher than 5-7V, you need to use separate (high efficiency) regulator to step down the voltage from your batteries for the servos.

Just do not use the same regulator to power your other electronics and servos. Your electronics need a regulator, but the motor inside the servo does not need a regulator and just runs off of whatever voltage you plug into the servo. Most of the power you plug into the servo goes directly to the motor. Some of it is split off inside the servo to a regulator to provide power for the servo electronics so you do not need to worry about that. If you plug the servo into the same regulator as your other electronics, it means you just plugged the noisy motor inside the servo straight into the same power that is powering your electronics.

If this is what you meant to say:
"I can use a seperate supply from a 7805 supply [for the servo]" and assuming the board of education has a regulator built on it, then yes this would work. This is the same as plugging your servo and regulator directly to the battery, and then plugging your electronics to the regulator.

Your second idea is not good. Because, assuming the BOE has a regulator for the electronics, what you just did is you are powering the servo and the electronics off of the same regulator. THe noisy motor inside the servo will likley disrupt everything- and chances are the BOE regulator cannot handle the servo current anyways. PLug the servo straight into the battery, and not the regulator powering the electronics.

 

Will I have to add a resistor to one of the basic stamp out puts or reverse one of the servos leads to make both rotate in the same direction when I add wheels to them? I heard from a Friend I will have to do something like this.