Simple, stand-alone, repetetive function indexer?

[awright]

I feel like a tourist sitting in a cafe at the base of Niagra Falls asking for a glass of water, but here's my very rudimentary question:

What is the simplest way to get a stand-alone, repetetive, trapezoidal motion, single-axis stepper motor indexer function?

My application is to move a precision wheeled carriage carrying guages in about 10 cm. increments along a railroad rail. Because there is an outrigger carrying an idler wheel along the opposite rail about 5 feet to the side of the carriage, the traction wheels are not in line with the center of gravity of the rig. For that reason, and to avoid loss of accurate gauging of distance travelled along the rail and to minimize stress, I want controlled acceleration/deceleration.

The second desirable but not vital function would be to have the indexer read a bank of digital selector switches on the carriage telling it exactly how many steps to move. This would allow fine-tuning of distance travelled in each increment in the field or changes in measurement increments, depending upon what we find in the field.

Power source for all functions will be a 12 volt gel-cell battery on the carriage with appropriate regulation down to required voltages. I would want the carriage to wait for a start command (momentary relay closure), move one 10 cm. increment, stop and wait for another start command.

I am fairly experienced at building electronic devices, mainly linear instrumentation with a smattering of low-level digital functions, but never got into microcontrollers or programming. Maybe it's time, as this appears to me to be an ideal application for a PIC controller. But before I try to learn PIC programming on a tight schedule, I want to be sure there is not a simple indexer chip out there that would offer these capabilities. I know there are many kits and modules offering rudimentary autonomous indexer functions, but haven't found one offering trapezoidal motion in programmable increments on a simple start command (although I suspect they are out there somewere).

I have plenty of stepper motors and stepper driver modules on hand, but no self-contained, programmable indexers that can run on 12 volts or less. I would expect to program the indexer in the lab (or hard-wire it) to carry out the trapezoidal motion function autonomously in the field, hopefully with the digital switch reading capability in the field, but possibly without if that is impractical.

Alternatively, is anybody familiar with program modules that would provide these functions and would speed up my learning curve to get something running with a Basic Stamp or equal?

Thanks for any suggestions.

awright

[Al_The_Man]

I think your biggest limiting factor is going to be the 12v as I assume this is for propulsion as well?
The PIC would be able to handle it, but for controlled accel/decel you need to know the total weight and max rates for accel/decel to calculate the inertia involved, I do not work with steppers, but I imagine they would be out with only 12v to work with, even with servo's, 12v is going to be limiting.
I sounds like this apparatus has some weight to it?
Do you need any Operator interface, keypad/readout?
Al.

[awright]

Thanks for your response, Al.

Yes, the battery will be for propulsion as well as control, but I could easily add a second small battery for the electronics alone if power isolation turns out to be desirable. I thought that a three-terminal regulator and capacitors would provide adequate isolation of the electronics power (5 volts?) from the noise on the battery bus due to the motor.

I don't have all the parts together yet, but I'm anticipating total weight of about 50 lbs. when everything is included. The carriage has ground steel wheels spaced at 1 meter.

I'm not looking for high performance, since the dwell at each increment for measurements to stabilize will probably be longer than the incremental travel time. But I don't want to waste time, either, since the longer the measurement series takes, the more thermal changes can occur in the environment and the carriage. I hope to make measurements over a distance of about 30 meters in about 10 cm. increments.

No, I don't anticipate having any operator involvement with the carriage once the measurement starts except initiation of each incremental movement, either by timing relay or remote control key fob.

Thanks again for your interest.

awright