3DOF Leg Inverse Kinematics Program for TI-83

[Tony]

It's time for me to study IK. learned lot through above discussions. sounds it's too complex to control 6 legs hexapod.

[Noodle]

Read this: http://www.learnaboutrobots.com/inverseKinematics.htm

Read over it a few times until you can really understand it. It's actually not that complex just for what I'm doing, what Matt's dynamic gait generator does on the other hand...

[Tony]

Read this: http://www.learnaboutrobots.com/inverseKinematics.htm

Read over it a few times until you can really understand it. It's actually not that complex just for what I'm doing, what Matt's dynamic gait generator does on the other hand...

Hi Noodle, so smart young guy I want to post the same site and I found you have posted it just 1 hour ago I google the IK and found this page this morning, spend hours to look at it formula, it is exactly the solution to the dynamic IK for 3DOF leg movement! hehe.... Now I got the formula (sorry I have turned the geometry back to school 15 years ago like I was at your age I realize that I need rewrite 50% codes to add dynamic function, painful !

I'll set 3 parameters for 1) Height of coax to the ground 2) distance of tibia end to the coax 3) Height of tibia end to the ground (normal is zero) use these 3 paras to calculate angle, then translate to pulse..... big job to do that as you need set max/min angle of each degree to avoid servo damage, so i need revise at least 50% code.

Thanks again, and thanks google... can't imagine the life without google

[Noodle]

Aha!

My aim (when I even get a hexapod, some would say that I'm putting too much effort even though I don't have a 3DOF yet), will be height of end effector, distance from end effector to body and distance from 0* on the coxa to EE. Meaning I can just set those distances, give me the angles and turn it into pulses.

Question Matt:
I want to use these servo's, not Hitec or Futaba and I've tested that they only work with Futaba horns. Is this going to be a problem when mounting them with the kit? I really want to use these because I can get 13kg/cm torque for under $20 AUD. Where as a HS-645 is $60. I already have two of these servo's, when I bought them to play with them a few months ago. They are digital and don't actually seem that cheap. And very strong. Yes, will I encounter problems.


It does seem I have a problem of rambling.

[Tony]

after few hours rework I decide adopt IK method as I can't get too much benefit from it since I don't have foot sensor for terrain detection. If hexapod walking on flat ground I just need record current angle of each joint. The IK is useful if you want to change height of the body (off road etc.) my current solution is use a rough % to change the angle of each joint and seems work, it's not accurate but compare to the rework of my engine, can't see benefit directly from the performance, but IK is the correct way, anyway.

[No1_sonuk]

Question Matt:
I want to use these servo's, not Hitec or Futaba and I've tested that they only work with Futaba horns. Is this going to be a problem when mounting them with the kit? I really want to use these because I can get 13kg/cm torque for under $20 AUD. Where as a HS-645 is $60. I already have two of these servo's, when I bought them to play with them a few months ago. They are digital and don't actually seem that cheap. And very strong. Yes, will I encounter problems.

I can field this one, I think.

I've used Cirrus 601BBs on the femur and Tibia of my MSR-H01. They have the same size/layout of horn as Futaba servos, so it may be relevant to you.

Check out this thread:
viewtopic.php?f=21&t=186&start=0

[Matt Denton]

Question Matt:
I want to use these servo's, not Hitec or Futaba and I've tested that they only work with Futaba horns. Is this going to be a problem when mounting them with the kit? I really want to use these because I can get 13kg/cm torque for under $20 AUD. Where as a HS-645 is $60. I already have two of these servo's, when I bought them to play with them a few months ago. They are digital and don't actually seem that cheap. And very strong. Yes, will I encounter problems.

Its difficult to say if the servos will be good enough or fit!, but you will need 6 x mini sized servos for the coxa.

Generally with servos the following goes "Buy cheap.. Buy Twice!"

[Noodle]

:O Didn't realise they were mini servos. Meh, I'll have to buy them. Anyway, these servo's are the same size as these HS-422 (standard size servos). I'm getting some servo brackets in the mail in the next few days, if they line up, then I guess it's safe to say it should fit. These servo's actually seem pretty good quality, digital with metal gears. But hey I don't really know a ton about servo's. I'll wait for the package then report back. If they don't fit, I'm kinda screwed though, because $60 x 12 = $720AUD. Which is alot of money in Australian, considering I earn 8.50$/hr at my fish and chip store.

Edit: and thanks No1_sonuk good read. I actually bought a packet of Futaba horns and they're matched for the servo. I"ll wait for the package, mind you, I'll be buying the kit regardless as soon as I get the moneys. Hopefully they work cause they're matched at 13kg/cm each, mind you that's at 6v.

[Noodle]

These servo's fit pefectly! As do the Hitec's, though I'm more swayed towards these:

http://cgi.ebay.com/2-x-MG995-Metal-Gea ... |294%3A200

At the moment. As these are what Jaycar (where I bought the servo's from) list my product as (though they are clearly not). Plus these are a steal, as I can get 12 for $134 with free shipping! It appears Tony used these in iDream, so i'm asking him as to their quality.

[Tony]

These servo's fit pefectly! As do the Hitec's, though I'm more swayed towards these:

http://cgi.ebay.com/2-x-MG995-Metal-Gea ... |294%3A200

At the moment. As these are what Jaycar (where I bought the servo's from) list my product as (though they are clearly not). Plus these are a steal, as I can get 12 for $134 with free shipping! It appears Tony used these in iDream, so i'm asking him as to their quality.

Hi Noodle, just clarify I do not use MG995, its price in China is close to USD 25/pc. So I choose cheaper one - Caster... the standard servos looks similar, but quality is different