Very confused...
AIman
Posts: 531
This should be simple but the more answers I get the more confused I become.
I want to run the Parallax 12 volt stepper motor with a BS2.
There have been diagrams posted showing mosfets and such, however there are still questions that there don't seem to be straight answers for.
If things are simply to hook up a mofset to a pin, hook the motor to the mofset and then back to the stamp, will there be a second mofset needed?
Do I run 12 v power before or after the mofset?
For some reason brain freeze is setting in on this. If someone would be very simple in expalning the circuit and parts that would be much appreciated.
I want to run the Parallax 12 volt stepper motor with a BS2.
There have been diagrams posted showing mosfets and such, however there are still questions that there don't seem to be straight answers for.
If things are simply to hook up a mofset to a pin, hook the motor to the mofset and then back to the stamp, will there be a second mofset needed?
Do I run 12 v power before or after the mofset?
For some reason brain freeze is setting in on this. If someone would be very simple in expalning the circuit and parts that would be much appreciated.
Comments
Post Edited (originator) : 1/27/2007 10:50:45 AM GMT
UNIPOLAR STEPPER MOTOR - more than four wires:
the armature is made to turn a little bit each pulse. all pulses to the windings are the same ground potential (created when your stamp sends a "1"). ·there are four pulses to a pattern. maybe 48 pulses to a full armature turn (7.5 degrees / step).
·
your BS2 would use four pins to supply the pattern of 1's over and over to an "amplifier" - perhaps a ULN2803 - you would be using only 4 of the 8 "amplifiers" within the ULN2803.
The pattern might be:
1 0 1 0
1 0 0 1
0 1 0 1
0 1 1 0 and repeat,·· ----· maybe 20 or 40 times a second.
each "1" causes the ULN2803's "amplifiers" to place a·ground potential·on an end of a winding - allowing current to flow to the always-connected center-tap --· the 0's simply turn it off.
BIPOLAR STEPPER MOTOR - four wires:
the armature is made to turn a little bit each pulse. again, there are four pulses to a pattern. there are two windings in a bipolar stepper motor. maybe 48 pulses to a full armature turn (7.5 degress / step).
your BS2 would use four pins to trigger two H-bridges - one for each winding. Each H-bridge requires both a 1 and a 0, and then later, a 0 and a 1.
this is not hard to do, either -·all is built into a chip - an L293D
The pattern might be:
1 0 0 0
0 0 1 0
0 1 0 0
0 0 0 1 and repeat.·· ----· maybe 20 or 40 times a second.
each "1" causes the H-bridge to place a positive voltage on a winding - each "0" causes the H-bridge to place a ground on the other end of the winding - this is accomplished within the L293D
you may build the innards of the chips with individual parts if you wish - perhaps for a science project demo, or such --- diodes that are required (due to collapsing magnetic fields) for efficient and non-destructive operation are already built into both the ULN2803 and the L293D.·· When using the chips, no extra components are required.
- your BS2 only has to supply the 1's and 0's.
also: read here now ---->·http://www.cs.uiowa.edu/~jones/step <---- this is a VERY good tutorial.
read the "introduction" -- read "basic control". then do, please - ask questions again.
tommy
Post Edited (tommy) : 2/1/2007 12:45:26 AM GMT
Here is the unipolar stepper motor that Parallax offers:
http://www.parallax.com/detail.asp?product_id=27964
All of the documentation, including program examples, can be found on the same page:
Regards.
Bruce Bates
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
<!--StartFragment -->
I have two steppers each with 6 wires, two are for power and the other 4 are control wires - looks identical to the picture of the Parallax stepper - any way, if each phase wire has a 60v n mosfet (the ones Parallax sells) with the power hooked up seperatly would that work?
In other words each pin to the stamp has a mosfet and the power is connected directly to a 12v supply.
An example -
First wire to power
Pin·2 to mosfet to motor
Pin·3 to mosfet to motor
Pin·4 to mosfet to motor
Pin·5 to mosfet to motor
Last wire to power.
.·· · you're getting warm.· six wires, you say - it is a unipolar motor.
.·· · yes you may - use a switch (transistor, mosfet, plain ol' ordinary toggle switch) to energize each half of a winding in turn.· each square in the drawing below might be one of your mosfets...
.···· but the drawing looks more complicated than the earlier ones, far above...·· because now you must add diodes...··· one around the winding to direct the collapsing magnetic field as each switch is shut off, and one around each switch to protect the switch itself - the collapsing field's current will more readily flow through the diodes rather than attack your mosfets from the wrong direction.
.···· you are at an earlier stage of electronic building - individual components.·· what happens is, is that companies see a need for the same configurations over and over again and, presto ! - they build a chip with all of the necessary components inside.· Your four mosfets and eight diodes are all included in a ULN2803 chip.··· For bipolar motors - the L293D chip also includes all of the necessary protection diodes.· and they're cheap ! - cheaper than purchasing all of the parts separately.····· simpler construction, less wiring.
.···· AND·your word, "phase" doesn't quite fit here.· stepper motors have many, many (24, 36, 48) ·magnetic poles in the piece (the stator) that doesn't turn.· when you have pulsed each winding once in the proper order, your motor has turned only to the next set of poles - not all the way around.· You still need your BS2 to supply the pulses - perhaps at 20 to 40 times a second (making those mechanical toggle switches I mentioned, only appropriate for a science class).
.···· stepper-motors are cheap and quiet - no brushes to wear out.· also, if it takes 48 pulses to turn a shaft once - and if that shaft happens to be a threaded rod - extremely fine accuracy of the final moving part is obtained.····· you are supplying the pulses with a computer - the computer can count the pulses and "know" exactly where that moving part is, at any given time.·· the drawback of stepper-motors over plain ol' ordinary motors is that they need a system of control.
.···· continue on, please - I would very much like to hear that you have built something -- in any manner that works.·· there is more than one correct way to do most everything.
.·················· tommy
Post Edited (tommy) : 2/1/2007 7:41:32 AM GMT
I started building robots before I knew where to find robot kits·and then it was a long time until I found a robot that could be programed - its been 10-15 years since my first contraption.
My first robot was based off switches being bumped and the legs turned on gears, one set inside the other for a total of 8 legs. It worked great right up to the time it went from the desk to the floor...
My robots have been everything from a small line follower to a 6 foot tall humanoid made out of PVC. I don't recommend PVC, it bends and bounces a lot.
All said and done, there have been 14 robots built which doesn't include hacking or reprograming robots and doesn't include projects that aren't mobile.
The other reason for AI is because at work·I learned a computer language without having a manual, any books or anyone to help me. I still have a lot to learn but so far can do what is asked of me.
As far as the project I am working on now - there are several different motors that will run off the stamp. Control for each motor is a bigger issue then getting the motor turning. There will be sonar and IR attached that will dictate speed of the motors based on the distance to the nearest object.
Anyway, learning doesn't scare me. Sometimes you just gotta beat your head against a brick wall.
it every time in my project i use L293d and SPARTANT -3E STARTER KIT BOARD to let the stepper point to specific position
can i put intial position for the stepper that return to it every time????
1. home the motor to a switch or hard stop, zero the counters, or
2. stop the motors at a known position prior to each power off, or
3. use some type of encoder that allows reading a fixed position and not relative position
You've already asked the same question in another thread and you've gotten some suggestions and comments. There are rules in these forums and one of them is that you may not ask the same question in multiple threads, particularly if you started a thread on the subject. Another rule is that this is a Parallax supported set of forums for support of Parallax processors. Correct me if I'm wrong, but it doesn't sound like you're using anything from Parallax. This isn't just a "we don't make it, we don't support it" kind of thing. It's also that the people who participate here are familiar with particular hardware and particular software and some things that may be true for Parallax's processors and software may not be true for what you have.
Mike