Quad

[Mitch]

Tom,

Can you share some of the details of where you are going with the quad - geometry, motors, props, escs...? The U of Pennsylvania video has enhanced my motivation!

[Tom]

Don't tell anyone yet


Link


More info: http://www.youtube.com/watch?v=xSudVsZOPR8

Even more info will be released on a separate wiki page and the weblog!

[Mitch]

Very cool - we want details so we can start construction!

[Mitch]

Thanks for posting the wiki. What props have you been testing with?

[Tom]

It's a small 8 inch propellor.
I will update it with pictures and links to the prop-shop in a few days.

[Maximus]

It's a small 8 inch propellor.
I will update it with pictures and links to the prop-shop in a few days.

Hello Tom,
First of all, a big "bravo" for your cool project !!!
For multirotors aricrafts (my main interest) can you drive 6 or 8 motors ?
For GPS functions, can you make fixed points and retrun home ?
@+
Maximus
ps: any autolanding in case of power or signal loss ?

[elkaim]

Hi Tom,

Out of curiosity, you said that you are doing the calculation at 300-odd Hz for this, but what ESC's are you using that can take the control this fast. Aren't they limited to 50Hz?

Thanks, G.

[Tom]

@Maximus:

This is all planned somewhere in the future.

@Gabriel:
Typically ESC's contain a microcontroller that updates the FETs at several kHz. Those microcontrollers decode the PWM pulse lengths without looking at the timing between pulses. Since a PWM pulse can be maximum 2ms (in practice), you can send a new one every 2.5ms. Believe it or not: it works! Currently I'm executing all my loops once every 0.003s and updating the PWM's at 400Hz.

[elkaim]

Tom,

Very cool to update them at 400Hz and have it work. Does that also work for your servos? I suspect not, but I was curious myself.

--G

[Mitch]

Interesting tidbit Tom. I've been searching for some numbers and data for ESC refresh rates. It is not a number published in the specifications by manufacturers, yet, it's critical to the stability and control solutions. Also, one of the problems I've been having with my vtol platform. I've been tempted to hook a few ESCs up to a signal generator and test their performance.

Do you know if these are typical numbers or specific to some ESCs? I know the chinese imports (turnigy) are supposed to work with the higher rates. I've shied away from those until recently.

I think most servos would do weird stuff with these numbers.