3 replies to this topic

[inxtremo]

Good morning, after successfully communicate with my stepper motors via N+, FTDI Breakout Board and a WPF application i wonder how to accelerate and decelerate my steppers in a smooth way. On YouTube exists several examples, most on the Arduino plattform. I found a class for Arduino too, "AccelStepper", which make such things possible. But how to do that on a Netduino? Should i port an Arduino code snippet to C#? Most snippets i see using float numbers for the delay between 2 pulses, but on C# i can only use Thread.Sleep(int). Any suggestions on this? Thanks and best regards, Daniel

[Paul Newton]

Hi there, I am used to working on DSP designs where it is sometimes necessary to step through an array of values at a fractional rate. For example, generating a sine wave with an arbitrary frequency using a 256 point sine wave lookup table that is stored in an array. To do this you need an integer index to access the table, but the index needs to increment (or decrement) in non-integer steps This sounds like a similar problem as you are trying to solve. The solution for generating a sine wave is to store the floating point increment in a variable and add it to a running floating point counter when each sample period comes round. To fetch a value from the array, we simply use the integer part of the counter. In the background the fractional parts will eventually add up to an extra step every so often and this gives the impression that the table is being stepped through at a non-integer rate. How does this help you? Stepping though an array at a fractional rate is similar to stepping through time at a fractional rate. Create a floating point millisecond counter variable. Each time you need to implement a delay between steps, take your desired floating point millisecond delay value and add it to the counter. Then, take the integer part of the counter and use it for the next millisecond delay. Deduct that integer value from the counter. Doing this will average out the fractional parts that you can't express in a delay of integer milliseconds, and the result should be a smooth stepper movement. Hope this helps - Paul

[inxtremo]

Hi there,

I am used to working on DSP designs where it is sometimes necessary to step through an array of values at a fractional rate.
For example, generating a sine wave with an arbitrary frequency using a 256 point sine wave lookup table that is stored in an array. To do this you need an integer index to access the table, but the index needs to increment (or decrement) in non-integer steps

This sounds like a similar problem as you are trying to solve.

The solution for generating a sine wave is to store the floating point increment in a variable and add it to a running floating point counter when each sample period comes round.
To fetch a value from the array, we simply use the integer part of the counter.
In the background the fractional parts will eventually add up to an extra step every so often and this gives the impression that the table is being stepped through at a non-integer rate.

How does this help you? Stepping though an array at a fractional rate is similar to stepping through time at a fractional rate.

Create a floating point millisecond counter variable.
Each time you need to implement a delay between steps, take your desired floating point millisecond delay value and add it to the counter.
Then, take the integer part of the counter and use it for the next millisecond delay.
Deduct that integer value from the counter.

Doing this will average out the fractional parts that you can't express in a delay of integer milliseconds, and the result should be a smooth stepper movement.

Hope this helps - Paul

Wow, thanks a lot.

I think at weekend i have the time to think about your answer in more detail. I´ll post my results.

So far, i re-implemented a method for trapezoidal acceleration i seen for the Arduino. Works fine but i´m sure there are lot of space to improve this.

Thanks and best regards,
Daniel

[ItsDan]

Depending on what you mean by smooth, a sine curve is really one of the simplest ways to model any kind of non-linear change in a value.