I just fine tuned my 3DOF T-Hex calibration and stubled upon a question.
Image 9 in the 3DOF T-Hex Tutorial tells me to calibrate the front and rear legs to 30 deg. The angle is measured between the middle leg to the corresponding leg.
But…
The angle also has to be defined in the configuration file. And this is referred from the center of the body (roll axis) to the leg which makes 60 deg. Although this is exactly the same angle, it could be confusing. Is it possible to change the image so the angle is referred to the body and has an angle of 60 deg as well?
PS. I talked to Zenta about the front/rear coxa angle. He uses an angle of 45 deg. As long as it is correctly defined in the software this will be fine. But it’s a good thing to decide on what angle to start with and build all T-Hex’s the same so it would be easy to exchange software.
The 4DOF is 45 degrees, but the 3DOF was set to 60 degrees. I’m not sure but I think it was easier to use Phoenix code for the 3DOF, but Kåre wanted to use 45 degrees on the 4DOF version.
I just want to say something about the calibration of the coxa. Ideally, I’m using the InitPosXX ([START POSITIONS FEET]) to define the coxa angle for coxa calibration.
Anyway, as long as the calibrated coxa angle correspond with the coxa offset in the code almost any angle would work though.
Just to be clear. In step 6 the legs are set to be perpendicular to the long dimension of the body.
Then in step 9 it says “Remove the center screws on the four corner hip servos (front right, front left, rear right, rear left), pull the servo horn off of the servo and rotate the leg outward 2 ‘clicks’, or 30°. Replace the screws when you are finished.”
Because we are telling them to rotate it 30 degrees from where it was, putting 60 degrees on the image might be just as confusing. If I got it wrong just tell me. I can take it. lol
Yes. I used 45 deg since the InitPositions of the leg give this value. But 30 deg would also work fine.60 deg works fine for Phoenix but its to much for T-hex IMHO.
I vote for 45 deg on both. Using the same angle is more logic when upgrading from 3 - 4 DOF.
I think I would vote for 45 degrees as well as I don’t understand any reason why the 3dof and 4dof should be different here. It would probably also make it easier to make sure we have one set of sources that works on both versions with only CFG file change. So it sounds like I need to move each of the 4 servos 1 more click? Likewise need to update the CFG files.
I also did some experimenting with the initial positions yesterday. I placed init pos of the front and rear legs further away from the middle legs. This gives more freedom when rotating. With the current setup the legs could easy collapse.
Zenta, Could you supply me the 4DOF init leg pos? I want to see if we can keep those identical as well.
The init positions are different from the ones I have. I also see that the front and rear legs are in a 45 deg angle with the same coxa tars distance (sqrt(72^2 + 72^2) = 102).
I haven’t tried them but I think this would be suitable.
I update my default coxa setup to 45 deg as well and try this init positions.
I’ve adjusted the rear and frond coxa’s with an offset of 45 deg.
The following changes are made in the configuration file
Init positions, so the leg will not collapse
Min/max angles, so the front legs can not hit the body
init coxa angle, for the new 45 deg offset
Jim / James, This will be the last changes for now on the cfg file. Can you update the file in the tutorial page.
If you have a spare 3DOF THex, try it on. You will be amazed by the difference it makes
