Hexapod Makeover

[blegas78]

Here's a better video of my hex, with PS3 Sixaxis controls.

[Demmo]

whoa! really cool - it`s the first time I see real steering via PS3 controller.. so far I have only seen body moves, rotation etc and you have put all that together and moves are connected with walking
moves are a little bit shaky (is it software or hardware issue?) but i really like the job you've done with controlling the bot - congratulations!

btw. nice video.. background music, subtitles, overall show - cool

2 questions..
- what do you actually do via your phone? is that programme some kind of BT terminal (commands via serial port)? i assume you use it to send commands instead of using pc/laptop with BT dongle?
- where is the PS3 controller connected? probably it's described in subtitles of the video but I have never seen that controller live and I don't know how the "second end" looks like on videos i can always see the controller (wireless I think) but I can't see the receiver.. or I see it but I don't know I am actually looking at that

[blegas78]

whoa! really cool - it`s the first time I see real steering via PS3 controller.. so far I have only seen body moves, rotation etc and you have put all that together and moves are connected with walking
moves are a little bit shaky (is it software or hardware issue?) but i really like the job you've done with controlling the bot - congratulations!

btw. nice video.. background music, subtitles, overall show - cool

2 questions..
- what do you actually do via your phone? is that programme some kind of BT terminal (commands via serial port)? i assume you use it to send commands instead of using pc/laptop with BT dongle?
- where is the PS3 controller connected? probably it's described in subtitles of the video but I have never seen that controller live and I don't know how the "second end" looks like on videos i can always see the controller (wireless I think) but I can't see the receiver.. or I see it but I don't know I am actually looking at that

Thanks Demmo, let me clear a few things up for you.

1.) The hexapod has a Fit-PC2 which is simply a small standard computer. People use these to install Windows or Linux(like me) to be used as a home theater PC (HTPC). It has a 1.6GHz Atom processor, GMA500 graphics; same basic computer architecture as most netbooks. The phone is using a secure shell (SSH) client to connect to the onboard computer through WiFi. I do this so that I do not need to connect a monitor and keyboard to the computer, and I can have all the capabilities I need by getting the "terminal" program of the computer wirelessly. BT is not used for this.

2.) The PS3 controller uses bluetooth for the connection, so there are no wires or other non-standard wireless components. I am using one of the USB ports on the computer for micro BT dongle, and it works great.

Yes, the movements are shaky, which is due to possibly a few reasons. The Robotis motors are very slick in that they have a huge range of 300 degrees, and that the motor control parameters may be adjusted. After talking to Matt Denton who has been playing around with these same motors, he has given megreat insight to possible operation to these motors. So shakiness is probably due to the following:

First, 10-bit resolution of the output results in poor overall resolution of positioning. As a result, any PID controller within the electronics will have poor performance. I have tried to give the motors decent control parameters, but right now they seem a little harsh.

Second, there exists a decent amount of flexibility in the physical hardware. As I keep saying, the thread-rod for the tibias as well as the little bit of femur flexibility causes the whole body to shake a bit. The current dynamics however are really not ideal, and really make the hexapod shake just about as much as possible. I worked on the dynamics last night to make this better, so the next video I take will hopefully have a more polished performance.

I'm glad you like the song! It is actually me that made the song (I am 12 Cent Dwarf). It's an older song I made a few years back, but certainly the best one i made at that time.

[Demmo]

thanks, now it's clear for me

can't wait to see the next vid

btw. i thought that these drives use rs485 for communication and positioning.. and it looks like i was wrong

[blegas78]

The RX-10 and RX-28 motors do use an RS-485 bus for communication, and the AX-12 motors use a bidirectional(half duplex) TTL level asynchronous serial bus. They do not use PWM signals like most standard RC servo motors. I made a USB board that interfaces the computer to both of the different motor busses.

[blegas78]

Turns out Compulab(the maker of fit-pc2) liked the hexapod enough to put a link of it on their site:

http://fit-pc2.com/wiki/index.php?title=Case_studies

[Demmo]

ok, so I don't get where is that mentioned 10-bit resolutuion problem If you have a board connected via USB which communicates with servos over some kind of protocol and you don't have to produce any PWM signal where the resolution problem could probably occur, where is that weak point?
i guess it could be inside the drive - does internal electronics use 10-bit DAC for positioning?

[Matt Denton]

i guess it could be inside the drive - does internal electronics use 10-bit DAC for positioning?

That's exactly the problem, the internal ADC on the RX-10/28 devices use are 10bit, which is simply not good enough when it comes to precise small movements. Also the servo control loop is pretty poor! I'm currently looking at adding a X 3 amplifier to the pot feedback circuit, essentially increasing the resolution by a factor of three, and decreasing the range to 100 degrees.

[Demmo]

very good idea for standard applications such swing (300degree) is unnecessary..

@Matt-> sometimes I wonder what do you do at work that you have so much time for such things or is it your free (after job) time? i like robotics and electronics very much but because of many duties all of my ideas go at a snail's pace

[BillB]

blegas78 wrote:

Here's a better video of my hex, with PS3 Sixaxis controls.

Great video. Very impressive hexapod & full Kudos for linking an iPhone/iPod Touch to a Hexapod.

I am very impressed with the form factor of the fit-pc2. I suspect that you may have started a trend of fit-pc2 hexapods.

blegas78 wrote:

I made a USB board that interfaces the computer to both of the different motor busses.

Very impressive. You may want to commercialise this (or open source it) because there will be a fair few people out there who would like to combe Robotis servos.