Electronically Controlled Drying Wheel

[Charles_Gantt]

Arduino Controlled Drying Wheel

redg8r and myself have been in discussion about creating a drying wheel that its controlled by a Micro Controller. With my background in discrete electronics and my hobby in robotics it shouldn't be that hard to accomplish. I have some basic design plans laid out below and would greatly appreciate input from the community on every step in this process.

Requirements

• Adjustable RPM (1-10?)
• Adjustable cycle time (1 hour -12 hours?)
• LCD Screen to display time left and RPM
• Enough Torque to turn large drying wheels (whats large?)
• Easy to retrofit drive system to existing wheels.

Electronics to be used

• Arduino Dev Board or AVR prototyping board.
• Low Voltage DC Motor (12v Max) (Stepper, Geared DC, or Continuous Rotation Servo?)
• 20x2 Character LCD. Parallel input.
• 2 button input system.

Drive Systems

I have 2 ideas for the drive system at this point and really would like some input on them.

Quieter and Cheaper Drive System

This drive system would use a Geared DC 15 RPM motor that would be driven by a transistor and controlled by an Arduino. The motor would have a 2-3" rubber covered wheel on it and this would mate up to a second wheel on the drive end of your drying wheel. The wheel size would have to be calculated to give us a max RPM of 10 or what ever the community decides is fastest useable RPM. Estimated cost to complete the electronics and drive system $50 +-$10

More Powerful, Louder, and Slightly more Expensive System.

This drive system utilizes a NEMA 17 sized stepper motor that would direct drive a length of 1/4" all thread that would serve as the axle that holds the drying wheels. By design stepper motors are a little noisy, and require a stepper motor driver chip in addition to the Arduino. This would be the easiest to design and would by far be the easiest to fine tune and maintain. I estimate this one at $50 +-$15.

Those prices are would it would cost for one to build this themselves using a pre built Arduino and Stepper Driver Shield. I could get the cost down some by building a custom PCB and eliminating the unused electronics.

Open Source Hardware Compliant

I am a huge supporter of the Open Source Hardware movement and was part of the initial OSHW Definition acceptance. This whole process will be thoroughly documented and the final code and design files will be released under the GNU Free Documentation License (still reading up on this so it may change.) so that anyone can make, modify or do as they please with the end product. So please feel free to speak up and comment on anything here that you think should be changed, amended to, or completely redesigned.

[Vodkaman]

Good project. I like the rubber wheel drive idea and the threaded drive on the stepper motor. The problem is always interfacing with the wheel spindle.

I have a stepper motor that I have wanted to use for projects like this one, but never managed to get it working. Do you have a drive circuit diagram you could send me to try (must be readily available passive components, no PIC controllers)? The motor is a 4 wire bipolar, so requires a H bridge driver. I am OK with the control circuitry, just the driver is stopping me.

Good luck with your project, I hope you get plenty of interest.

Dave

[Charles_Gantt]

Good project. I like the rubber wheel drive idea and the threaded drive on the stepper motor. The problem is always interfacing with the wheel spindle.

I have a stepper motor that I have wanted to use for projects like this one, but never managed to get it working. Do you have a drive circuit diagram you could send me to try (must be readily available passive components, no PIC controllers)? The motor is a 4 wire bipolar, so requires a H bridge driver. I am OK with the control circuitry, just the driver is stopping me.

Good luck with your project, I hope you get plenty of interest.

Dave

To control a stepper you need a stepper driver like the A3967, This driver will need to see a PWM signal and the only way I know to provide a controllable PWM signal is by using a Micro Controller such as an AVR, PIC, ARM or the like. I will be using an Arduino or an Arduino Variant for this project, and the Arduino is based around either the Atmega 8, 168, or 328 uController. There are variants called Arduino Mega which provide more flash memory and more I/O but for this project even an Atmega 8 is overkill.

I am leaning more towards the Stepper Motor setup because the more I look at it, brushed DC motors will not last long with 10+ hours of use daily while being under volted to control speed. They also do not have much tq at start up where as a stepper has the TQ we need.

This is the stepper driver board I am considering using. I have used it in the past and its about as cheap as they come.

http://www.sparkfun.com/products/10267#

[redg8r]

Hi Charles,

Any reason to discount a servo? I ask because a servo would negate the need for a driver/bridge.

But isnt a servo simply a dc gearmotor? maybe cycle time was an issue?

Thank you for taking up the project. I was discussing the arduino with a few members at the annual meeting and received some odd looks

But I think once the community sees what this lil dev board is capable of, we'll see interest in adapting it to increase production, or make mundane tasks in our production much simpler.

Couple more questions:

1) A full blown mega or even a duemilanove seems overkill. Could we use a smaller board like a mini?

2) which type of board is most versatile? the uno?

Thanks

[Charles_Gantt]

Hi Charles,

Any reason to discount a servo? I ask because a servo would negate the need for a driver/bridge.

But isnt a servo simply a dc gearmotor? maybe cycle time was an issue?

Thank you for taking up the project. I was discussing the arduino with a few members at the annual meeting and received some odd looks

But I think once the community sees what this lil dev board is capable of, we'll see interest in adapting it to increase production, or make mundane tasks in our production much simpler.

Couple more questions:

1) A full blown mega or even a duemilanove seems overkill. Could we use a smaller board like a mini?

2) which type of board is most versatile? the uno?

Thanks

Well after talking to a few friends about the servo, I became concerned about lifespan with such a long cycle as well as being able to control its speed. Most thought that 1-10 rpm would be too slow to achieve and still have enough TQ to turn the wheel. I was told that they get hot fast and unless you get one with metal gears, it will wear very fast. Continuous rotations with metal gears and decent TQ are very expensive. I found 3 in a quick google search and even being Chinese brand they were still quite expensive. So after weighing my options I went back to the Stepper or DC Gear Motor ideas. Personally I like the idea of the stepper because they can be had in single quantity for about $14 shipped on ebay and a $14 driver board, then the $20 AVR Proto Board from Protostack.com puts us at $48 for the motor and drive electronics.

A geared DC Motor (15rpm) can be had for $10 + 5 shipping, then you would need a $15-20 driver board to get the RPMs down. You could PWM a transistor but its not as effective as using a bridge to control it. I think the lowest you would be able to run the gear motor with out a driver board would be 5RPM.

The Arduino Mini is a normal Arduino with a Atmega 328 or 168 and everything is SMD instead of having a DIP chip, thus the board is smaller. The Uno is the basic Arduino now. Other than a new USB - Serial chip, it is the same as a Duemilanove or the Decimilia. Both of which are the Uno's predecessors. If you are looking for one to play with get a Uno. Adafruit.com sells a nice starter kit with a few documented projects to get you started.

The board I plan on using is a plain AVR Atmega 168 prototyping board I will burn the Arduino bootloader to. So it will be a basic Arduino that is a little harder to program as it has no USB - Serial chip. I will actually use an Arduino to program it. Its this board. http://www.protostack.com/boards/microcontroller-boards/atmega168a-development-kit?cPath=26

[redg8r]

Since you're doing the offset drive, I'd like to tinker with a direct drive option. Going from your recommendations, a stepper with some sort of shaft coupler.

For this wheel we want to control:

1. on/off
2. speed (rpm)
3. runtime

Correct?

Once you've sourced a display, pass us a link. That's about the only component I'm completely unfamiliar with.

[Vodkaman]

Cost is going to be an important factor for most people buying this kit, so a lot will depend on the cost of the display. I really like the stepper motor option. It is the more expensive solution, but for an all singing and dancing turner, I feel that it is the best solution.

The rotation speed is probably going to be between 1rpm and 10rpm. The duration is probably going to be between 1 and ten hours. To satisfy both of these control and display conditions, I would be using a single push switch and a single 7 segment LED array, in conjunction with a decade counter. The push switch will increment the count (0 = 10) and rotate back to 1. Either two sets can be used or a function switch. Probably two sets would be simpler and clearer.

This solution is cheaper, but it would obviously involve labor to assemble and solder the components. The circuit board would be slightly more busy, but that only gets designed once. But at the end of the day, a modular display will look more professional and the labor saving may well make it the most cost efficient solution.

In addition to the : on/off : speed : run time : controls, I think a pause button would be a useful addition, allowing the user to temporarily pause the wheel, to add a lure.

Given your markets resistance to tech, I suggest you keep things as simple as possible.

This design will obviously appeal to rod builders also, without any changes. But the basic design could well be adapted for those interested in duplicator machines. This application would require more switch control, but possible. Of course the market for this application would be very small and may not worth the effort.

Dave