Servo controlled velocity stack on racebike

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Cedric
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Servo controlled velocity stack on racebike

Post by Cedric » Wed Feb 13, 2008 10:04 pm

I don't know where to look but this seemed like a good place. I need help designing a stepper motor that is controlled by engine RPM. It's for a single cylinder racebike with 12volts available. The signal is once per revolution and I need the servo (or stepper) to start moving around 9000rpm and be done by 13000rpm. I can handle the physical construction but I need help with the electronics. Even if you can just point me in the right direction I would be most grateful. Thanks.

Bigglez
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Re: Servo controlled velocity stack on racebike

Post by Bigglez » Thu Feb 14, 2008 11:48 am

Greetings Cedric, and welcome!
Cedric wrote: I need help designing a stepper motor that is controlled by engine RPM. It's for a single cylinder racebike with 12volts available. The signal is once per revolution and I need the servo (or stepper) to start moving around 9000rpm and be done by 13000rpm. I can handle the physical construction but I need help with the electronics.
Interesting project, I have a few questions.

(1) Have you picked a candidate stepper motor yet?
(2) How is the engine speed signal developed?
Is it a mechanical closure, an electrical pulse from
another electrical circuit (already in place), or is
it a non-contact electrical pulse (optical or magnatic)?
(3) When the engine reaches 9k RPM does the stepper
move once, more than once, or continue to move
until stopped by another criteria?
(4) When the engine reaches 13k RPM does the stepper
stop and rest or does it reverse and return to the
9k RPM position?
(5) What does the stepper do below 9k RPM?

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haklesup
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Post by haklesup » Thu Feb 14, 2008 12:54 pm

I like to break problems down into bite sized pieces, so looking at it from a block diagrammatical point of view.

First you need signal conditioning. That is something to take the RPM pulse signal from the engine and scale it to TTL voltage levels for input to the next block. This may end up being a fairly simple circuit depending on the source of these pulses. It may just be resistors and diodes or it may require an active component like an op amp or transistor.

Now that you have a 5 or 12V square wave, it can be applied to the input of a PIC or uController which can count the pulses and divide by time to determine RPM. Any offset of scaling can be dome in code (firmware) at this point. With that data, you can compute and output any valid commands to the motor.

Final block is a stepper motor controller followed of course by a motor. A stepper controller can have serial or parallel data control input. This determines the interconnect requirements and ultimately the part number for the middle block.

Bigglez questions are all essential in selecting the components and developing the algorithm for moving the motor.

Dwelling on component selection for a moment. Choose a stepper controller that makes interface easy. You might even be able to find one with the uController built on-board (a robotics or programmable controller might be the class). There is a very wide range of features available in the "programmable stepper controller" category, just search on that.

Some examples http://www.anaheimautomation.com/indexers.aspx Their PCL501 will probably do the job

The PIC only needs enough inputs and outputs to interface with the sensor and stepper controller and enough memory for your code. Once you spec those things, you can search for a part to fit the bill.

One more thing. Depending on the stepper you use, you may need additional power supply beyond what the bike has. If you're just trying to drive a small pancake stepper (like that which you find in a printer) to control a throttle or choke, then you shouldn't need much amps.

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