Standalone Joystick Stepper Control

[kochevnik]

I have a project I am beginning to work on. I want to use a joystick (without a PC) to pan and tilt a 20 to 30 pound table . I figured I would use a gearing system for the motor to provide more torque and that I was shooting for rotatating the table 180 degrees in about 2 to 5 seconds.

I know that an oscillator (555) circuit could be used to send signals to the stepper drive, but all of the designs I have seen that use this circuit use a potentiometer to set the speed of the motor and then use switches to turn the rotation on or off. That's not what I want.

What I want is to be able to use a standard joystick (with pots) to change the speed and direction of the table's rotation. Move the joystick a little and the speed is low, move it farther and the speed increases proportionally.

I searched for DAYS on google and the best thing I found so far was here:

http://www.imshome.com/osc.html

This seems like it would do the trick, of course not real cheap either

Anybody have any better ideas / suggestions for accomplishing this ?

And on a side note, using bipolar motors for the 20+ pound table what would you recommend for sizing the stepper motors ? ... besides bigger is better

Thanks,
Matt

[j m]

Could you not use multiple 555’s controlled by a separate switch, to say three different speeds one for each speed. set at: slow medium and fast.

Link, may be helpful? http://www.buildyouridea.com/hardwar.../joystick.html

Sorry I cant be more help jm

[CJL5585]

What you need to use is a VOLTAGE CONTROLLED OSCILLATOR (VCO). The applied voltage as it increases sends out a square wave frequency in proportion to the voltage applied.

The joystick pot would be used to vary the voltage to the VCO. The output of the VCO would be used as is or amplified to create the steps to a stepping motor.

Do a search on VCO integrated circuits.

I know Motorola, Texas Instruments, and several other companies manufacture them.

I can not offer any more assistance than this.

[ynneb]

Sounds like you want to be able to move a telescope or a surveylence camera.

I would not be using steppers or servos, but simple DC motors.

This will eliminate the need for pulse control. That way you could simply uses a variable voltage controller, similar to what you might find on a model railway.

[smarbaga]

several microcontrollers have multiple analog to digital converters which you could use as joystick pot position detection.
a simple voltage dividing cct with the pot wipper tap into the adc would work perfectly.
the micro could output signals to your motor controller, be it by wire or wireless to a dc pm motor, stepper or ac motor.
even screw jacks, the kind that are on hospital beds may fit yout bill.

[Evodyne]

Originally Posted by kochevnik I have a project I am beginning to work on. I want to use a joystick (without a PC) to pan and tilt a 20 to 30 pound table . I figured I would use a gearing system for the motor to provide more torque and that I was shooting for rotatating the table 180 degrees in about 2 to 5 seconds. Thanks, Matt

Matt,

I think you need to answer this question: is the table to follow the joystick's position? Examples-you push the stick forward, but only halfway. The platform tilts from its upright position forward 45 degrees and stops. Then you push the stick the rest of the way forward. Now the platform moves till it is tilted over to 90 degrees. Let the stick go and the platform returns upright.

Or just the speed setting? Example:you push the stick forward, but only halfway. The platform begins to tilt forward at half speed, but continues moving till you let go of the stick. When you let go of the stick it stays where it is.

I just want to make sure I understand what you are trying to do. If it's not being too nosey, what's the application?

Evodyne

[smarbaga]

to move a servalience cam, go to the auto wreckers and pull the electric mirror control
they are cheap and work great.
for heavier movement the workings of an electric drivers seat.
there is a wealth of stuff at the auto wreckers for small movements (electric door lock solenoids and the likes.)

[JavaDog]

Originally Posted by smarbaga to move a servalience cam, go to the auto wreckers and pull the electric mirror control they are cheap and work great. for heavier movement the workings of an electric drivers seat. there is a wealth of stuff at the auto wreckers for small movements (electric door lock solenoids and the likes.)

That is really damn clever - never thought of that!

[kochevnik]

Some great ideas ! Thanks everyone.

I think you need to answer this question: is the table to follow the joystick's position? Examples-you push the stick forward, but only halfway. The platform tilts from its upright position forward 45 degrees and stops. Then you push the stick the rest of the way forward. Now the platform moves till it is tilted over to 90 degrees. Let the stick go and the platform returns upright. Or just the speed setting? Example:you push the stick forward, but only halfway. The platform begins to tilt forward at half speed, but continues moving till you let go of the stick. When you let go of the stick it stays where it is.

The second is what I want.

My reason for going for steppers vs. DC motors was :
1) I am more familiar with steppers having worked on them when CNC'ing my mill
2) it was my understanding that most DC motors were more for high speed rotation, and that there wasn't an easy way to make the motor stop and hold position
3) I thought that DC motors would be harder to find the right one and higher cost
4) I thought the steppers would be easier to position more accurately.

Maybe I am wrong about some / all of this ? Opinions, please ?

I should also mention that power requirements are a factor here too. The system will someday run off a battery/ PV system and the lower the overall power usage the better, althought the system will not be on 24/7 but just on demand maybe once or twice a week for a few hours at a time. I know that with a stepper motor they will draw power even in the holding position, altho with some controllers, the current can be set to drop to 30,50,70 percent after a second or two if the motor isn't moving. I do need the system to hold position, so it's either steppers, DC motors with some kind of powered brake (still sucks power) or some type of clever system of locking the position either with using some type of mechanical brake or low powered solenoid/brake system, which seems to add complexity. Having to choose between using a little more juice or added complexity, I'll choose the juice as system reliability is very important as well.

It just seemed to me that a stepper system with idle-current reduction would be the simplest way to go. I'll use whatever works, but I need as many opinions as possible so I can sort it all out.

Thanks,
Matt

[Evodyne]

Matt,

Hi! O.K, let me suggest something simple, that might keep the price down as well. You want to move a fairly good weight, so you'll need some gear reduction for sure. And you want it positive locking. A worm gear setup does both! Hmmm...where can a cheap part be found: old car power window units! They are a "unit" consisting of a 12V DC motor (NOT a stepper) driving a worm gear meshed to a round gear. This gear has a shaft that moves the window mechanism. See attached pictures. A bonus is that they have mounting provisions.

For driving them you need a speed controller. Here is one that can handle two motors. Now, it doesn't just hook to a potentiometer or a joystick, but that can be handled easily enough. I'm really pressed for time right now and need to get going NOW, so the rest will have to wait. More later...

Lance

[jans123]

Hi! I just want to add a warning here. Those DC motors used in the automotive industry (windows, wind-screen wipers etc.) some times have the chassis connected to one of the poles. (At least the wind-screen wiper does). Be careful when assembling the unit and make sure you don't get a short cirquit. The window mechanism motor might work well. I like the idea.
(Sorry about my spelling, but Engish isn't my native languague)
/Jan Sjöholm/Sweden

[jans123]

Hi! A simple VCO doesnt solve the problem. You will need a lot of "glue" to build a discrete cirquit that solves this problem, but it can be done. I built something like this years ago for tilting swash-plates in hydraulic pumps, but today I would use a programmable micro-controller like the AVR-chips. My advice: Find someone who could help you program a AVR-chip and you could wire up a complete control system for several axes and a couple of joysticks with less than ten components.
Doing this, you could even let the AVR send pulses either to a control circuit for stepper motors or you could let the AVR control power transistors connected to the stepper motors directly or you could use simple H-bridges to power DC motors for window elevators suggested by another gentleman elsewhere here.
The program can't be that complex. Probably a student could do it as an exercise.
(Sorry about my typing, but English isn't my native languague)
/jan sjöholm / sweden