Project Builder

michelvh

I hope this is an appropriate topic for general discussion. I couldn't find another spot that seemed better

I know just enough about the Parallax products to know that my project that I need for a science center can be made, probably with a basic board.
I have no idea how to do it and I don't have time to learn. My old guy isn't available anymore.
I need someone to build and program for me. Someone with more than a few projects under their belt.

Roughly it is a reaction timer. When you press the start button a pseudo random delay starts. Then 10 led lights fire off one at a time for approximately .05 sec each.
If you hit the stop button before the end of the sequence a dry contact causes an audio file to play on my digital player. If you are too slow a different sound plays. CFSound III Compact FLASH Digital Audio System with built in Amp & Two Contact Sense Input Triggers

Repeat

Mike

erco

Mike: That's an easy job for a Basic Stamp 2. A BS1 could do it, except that you want 10 LEDs. We could walk you through it online if you want. Do you already have your Stamp? For $29, this kit with a Homework board would be a good option for you.

http://www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/789/Default.aspx?txtSearch=homework+board

Duane Degn

What you describe would be easy with a Stamp or a Propeller (Propellers cost less and can do a lot more though).

If you've already worked with a Basic Stamp then I'll agree with erco that that would be the route to take.

A Propeller could take care of the sound playback as well as the LEDs and timing if you want a more cost effective solution than using the CFSound II system.

If you could find an AP-16+ Audio Player, you'd have just about all the hardware you need.

A PropBOE would just require an amp to boost the playback volume. It could play back wav files from a uSD card.

The LED and timing part of your project would be trivial and as erco suggested there are several of us who'd be glad to help with the coding here on the forum.

michelvh

Whew thank goodness for autosave - I thought I lost this all.

This all sounds wonderful but my old guy that I mentioned before was my tech and he did all of the wiring and programming.
I have an understanding of how it works and what it can do but I have never done it hands on.
And the last programing I have done was Basic on my Apple IIc.
I do have a basic knowledge of If then else loops variables counting and sort of how timing loops work
I have been wanting to try my hand at this though so maybe I will give it a try.

So the parts that I didn't mention are probably easily doable as well.
If the stop button is hit before the sequence ends the last light when the button is hit stays on until it is reset.
The reset time will be several seconds.
When that happens the last light on the display goes out and the light on the start button comes on.

OK so I looked at the kit and thought of 2 more projects that it could handle mostly.
Two the same. 12" turntable weighing about 5 lbs. Each time you press the button the table rotates 30° fairly quickly.
I need it to have a "home" of some sort so that one of the 6 items on the turntable is facing the right direction.
I'm pretty sure that the included motor isnt' heavy duty enough. It will be operated up to 2000 times per day.
What would you suggest for a suitable motor.
Ordering one kit now
Expect more questions
thanks for your help so far

SRLM

Servocity has good motors sets and the mounting hardware to go along with it. I'd take a look at this, with a 90-100RPM motor: http://www.servocity.com/html/gearmotor_gearbox.html
If you need the precision, I'd take a look at this: http://www.servocity.com/html/p785_super-duty_pan_system.html


The specifications that you gave are a bit ambiguous, and with more information we can provide a more detailed response:
1. "Fairly quickly" is relative. What is the maximum time for those 30 degrees?
2. How is the 5 pounds distributed? On the axis of rotation, or on the edges of a disk?
3. Will the turntable be expected to go in complete circles, or can it rotate a maximum amount in each direction (DC motor vs. Standard servo)
4. How precisely must you get the "home" position?

michelvh

1. 1 to 2 seconds
2. On the edges, but the disc itself will be on shaft and bearings. Motor only needs to provide rotation. Could be direct or timing belt drive.
3. Complete circles
4. Just kind of a guess at this point but probably +- 5°

Oh I see. The gearbox with the round ABS arm may be good as is with ball bearings and SS shaft on the driven gear.
The P785 with the acetyl gears I would stay away from. Plastic gears with the volume of start stop cycles I have would not hold up as well. Like 500,000 per year
I would rather have tougher components and not have to work on it for a couple of years.
I have used motors similar to the 6-12v dc precision motors many times and they typically last about 2 years in the hands-on science center environment.
Usually the output shaft bearings go bad first

The motor project is going to be easier than the LED project isn't it?
Can I test it with what I get in the parallax kit or do I need to go ahead and get the final stuff?

I know I need the gearbox, disc, and motor. Which RPM do I need? Lets call it 1.5 seconds for 60° (30 was wrong, I need 6 stops)
Manually variable speed would be nice but not necessary.
Is there any other hardware that I need?

Just thinking out loud -- would it be possible to ramp up and down the speed of the motor so it doesn't jerk starting and stopping?

SRLM

Another question is how you want to control this turntable? What sort of feedback mechanism do you need? I see two cases:
1. The user presses 1 of 6 buttons, and the turntable rotates to present that spot.
2. The user presses a button (or turns a knob, etc.) until the turntable rotates to the correct spot.

Case #1 will require some sort of microcontroller control, while the second can be done very easily without any programming.

Case #1
The motor project with control isn't too difficult. The main challenge will be to accurately position the turntable. I would do it by using a encoder mounted on the turntable itself.* The encoder would be either printed on plastic, or laser cut from a thin, black plastic and given a white background. The encoder disk would then be mounted to the underside of the turntable.

*This might not be the best method if the underside of the turntable is accessible to the user, since they could damage the encoder. But you could always make the diameter of the encoder smaller (at the expense of resolution).

Repeatability might be an issue with encoder based solutions: it might lose it's position, and then be unable to tell which "spot" is where. Since the disk is large enough, you could add a 3 bit designator to the encoder that labels a specific position. All together, this would produce a reliable (and non contact) system.

Take a look at the picture under "How to make an encoder wheel": http://www.societyofrobots.com/sensors_encoder.shtml

As for speed: You can always run the motor slower than it's rating, so I would err slightly on the side of a higher speed motor. 6*1.5 = 9 seconds per rotation, or ~6RPM. The gearbox has a 5.25 reduction, so thats roughly 6*~6, 36 RPM for the motor. So, I'd get the 45 RPM motor.

To control the motor you need a motor controller. With a motor controller you can adjust the speed of the motor to suit (actually, it's the average applied voltage which is proportional to speed for no load situations).The 10RPM motor is 12v and 1A maximum. To be very reliable, I'd heavily overspecify the controller. Something like this would work: http://www.pololu.com/catalog/product/1377 This controller also has the option of programming acceleration (ramp) limit values, which is handy. If you use a different controller than a microcontroller can do the acceleration.

To power the motor you'll need a 12v supply. The easiest solution would be to use a commercial OTS 12v switching power "brick", commonly used with electronics. The can generally souce several amps, and are reliable and inexpensive.

Case #2
I would use the same motor, motor controller, and power supply from above. For the user input the controllers have an analog input. Combined with a simple circuit and a joystick, potentiometer (knob), or buttons of your choosing, you can control the motor.

---

I do contract programming and embedded system design with the Propeller. If you're interested in hiring a contractor, we can discus this further via email or phone.

Also, what "Parallax kit" are you referring to?

michelvh

Sorry. I've been up to my eyeballs.
It's 1 button.
One touch rotates the table to the next position of the 6 position
With an encoder it would always land on one of the positions.It is not synced with anything els so there is no sync issue
A couple of degrees difference is not a problem.
If I just do a wheel with 6 white strips and a reflective sensor that should work right?
The only thing I'm not sure about there is if they press the button and release it quickly how do I make the motor run at least long enough to get past the light area or can I make the white small enough that it will turn the motor off but the motor drift past it slightly so that it is ready for the next button push and position? Or will the motor controller take care of that for me?

12v power supplies are not a problem if they don't have to be switching. I buy them by the hundred for led lighting. Other wise I'll go with your suggestion

I am getting the Basic 2 Parallax as recommended by others for the Ten segment reaction timer. Probly will receive it tomorrow.