Angle offset of Phoenix Chassis?

[tom_chang79]

What is the angle Φ?

My GIMP angle tool state 60 degrees, is this correct?

[zoomkat]

I put a plastic protractor on my monitor screen and the angle as drawn looks to be ~63 deg.

[zenta]

Hi Tom,

Well I did setup my Phoenix a bit different, see this picture (hope its ok to use yours ):

I posted a similar question on my Project Phoenix thread:

@zenta

But I’m a bit uncertain about how to calibrated the front and rear coxa servos. When I calibrated my Phoenix I placed the coxa servo with its centre position for travel (1500) in the position that gave the front and rear leg as much travel as possible without crashing into the body. (sorry my bad english…). For my Phoenix that means an offset of about 42 - 45 deg (EDIT: relative to the Y axis). Since powerpod for Phoenix is not available yet I’m wondering what offset Jim or Laurent used for their Phoenix?

Answer from Jim:

@Robot Dude

We used a uniform 60° angle for the chassis holes. The Hitec servo spline has 24 teeth, which means there is 15° between positions. You should be able to position the servos to 45° with no problem.

Let me know if this makes any sort of sense at all.

[sienna]

Yes, it is 60 degrees. (I did the 3D model for Jim, so I measured it back then.)

I have those pictures that show all the offsets if anyone wants to host them.
(my web host is down because I have been too lazy for months to fix it)

[zenta]

ehm I think I misunderstood your question. I thought you also meant at what coxa angle you set the middle position for the servo (1500). Did you align the middle position (1500) with the 60deg offset of the chassis?

[sienna]

Posting here too:
Oh heck, I will just (ab)use the TR image hosting and post it here
forums.trossenrobotics.com/gallery/files/1/6/8/5/lm_phoenix_dimensions_57404_thumb.jpg

forums.trossenrobotics.com/gallery/files/1/6/8/5/lm_phoenix_dimensions_2_475253_thumb.jpg

[tom_chang79]

I figured it was 60 degrees. Zoomkat, I measured 63 degrees initially with my GIMP angle tool, but I figured it was due to the picture being at a slight angle, so I rounded it to the nearest 10s of degrees…

Zenta, yes, I did mount it at 60 degree for the center for all the servos on four corners. What I’m trying to do right now is given a global coordinate (Xg, Yg, Zg), which is the coordinate with the origin at the center of the body (where the origin is in the picture), I’m transforming that coordinate into each local coordinate (Xl, Yl, Zl) since I have my IK-engine for the legs up.

Once this transformation is done, I just feed all six sets of local coordinate into my IK engine, to make the legs move.

Of course, to make it walk, I can’t just directly translate it. Each tripod have to alternate, so each tripod will be alternated. I figured, each tripod will have to move in half-circle motion, with the two sets of tripods 180-degrees out of phase with respect to each other, in order for the body to move forward. But this is an alternating tripod motion, I’ve also been very interested in the ripple-gait scheme that Matt Denton, and you, Kare, have been using on your hexapods.

The ripple gait scheme makes it look more fluid look, and I ultimately want to have both the tripod and ripple gait scheme in my bot and to be switched at will…

Do you have any tips for me on walking schemes for the ripple gait? The tripod is the most obvious and straight forward, but the ripple gait one perplexes me…

[zenta]

Hi Tom!

Your progress sound great!
If you take a look at my PEP manual you’ll get some more information about the ripplegait. Also visit the oricom (don’t have the link here) for more info.