Hexapod V4b

Hexapod Robots

Hexapod V4b

Postby Matt Denton » Wed May 21, 2008 10:25 pm

Built in 2004/5, another of my Aluminium hexapods, V4c is more or less the same as V4, but with different tibia servos and without the contact sensors. With the addition of a pan/tilt head, CCD camera and other bits 'n bobs This hexapod went on to become iC Hexapod. A couple of interesting features of this hexapod are the unique coxa design and the direct coupled servos.

Image

[youtube=5hbAMFAnui4]Hexapod V4b Video[/youtube]


p.Brain-ds

This is probably the most significant addition to the hexapod. The p.Brain has been in development for some time but the PIC18F version lacked the processor power to perform body rotation/translation and terrain adaptation and only ran at 30Hz refresh.

With this version, the same engine that previously ran off-board on a DOS machine, now runs on-board on the p.Brain and at refresh rates up to 100hz.

The pBrain-ds is being developed as a single solution to any hex or octoped with 3DOF leg arrangement. The p.Brain not only does all the leg locomotion, inverse kinematics, body rotation/translation and terrain adaptation, it also incorporates 24 channels of hi resolution PWM outputs, so no need for an additional SSC! and 8 analogue/digital inputs for ground contact sensors.

The p-Brain-ds can be user configured to different leg geometry and servo types via terminal software that gives endless configuration for any hexapod design. All that changes between designs is the motherboard that the p.Brain-ds plugs into. The motherboard supplies power, serial connections and distributes the PWM signals around the body. Control of the locomotion engine is via simple serial data, either RS232 or TTL level at 9600 or 19200bps.


Bluetooth control connection

The control connection to this Hexapod is through a simple bluetooth serial port via the p.Brain-ds TTL control port. The p.Brain has two serial ports that can be dip switch configured as either control data or terminal data. In this case both control and terminal data are mapped to the same TTL port. There are future plans to add I2C control communications.


Unique Coxa Design

Image

This hexapod has a unique coxa design which came about through having to make the body depth as small as possible for the V4 hexapod. Take a look at the picture above. You can see that the lower body segment is not below the coxa, but inside the coxa! This not only allows the body depth to be smaller, but also gives the added benefit of being able to remove a leg by unscrewing the coxa servo horn without the need to remove the lower body. Very useful while calibrating and for repairs!


Direct Servo Coupling

You may also notice that there are no servo horns being used! This design has had the servo spline punched directly into the Aluminium femur and body.


Future Plans

There are vague plans for this robot to go into the Kinetica museum, London. The idea is that there will be a head added with a CCD camera which will face track people watching the hexapod. However it will be within a glass case so it will not be walking around.


Tech Stuff

Servos: Futaba 3002/9206/9206
Battery: NiMh 4.8V 2700mah
Servo Driver: 1 X p.Brain-ds
CPU: dsPIC30F4011 (58.96Mhz)
Radio Link: bluetooth
Weight: Aprox 1.8Kg (with battery)
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Re: Hexapod V4b

Postby ucaboys » Wed May 28, 2008 4:29 pm

Matt,
I'm a software developer in Central America and I came about your webpage through a video on youTube.
Your project is very interesting, I've always liked many legged robots specially revered-jointed ones. Would it be posible to build one of these and have it act like a Pleo? I would love to build one.
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Re: Hexapod V4b

Postby Matt Denton » Wed May 28, 2008 4:40 pm

ucaboys wrote:Matt,
I'm a software developer in Central America and I came about your web page through a video on youTube.
Your project is very interesting, I've always liked many legged robots specially revered-jointed ones. Would it be posible to build one of these and have it act like a Pleo? I would love to build one.


Hi, and welcome to the forum!

I'm currently working on an aluminium kit version based on the v4b design, along with the p.Brain controller. I have not played with a pleo, and so wouldn't know exactly what it does, however, I would imagine that if you added the right sensors in the right places, with custom programming you could make it do more or less the same?

I will post details of the kit version soon.

P.S. have been having topic notification problems, if you have subscribed to this topic, and do receive notification, please let me know :)
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Re: Hexapod V4b

Postby ucaboys » Wed May 28, 2008 6:43 pm

No problems here with the email notification.

I'll look forward to the kit. I would also like to help out with the software if that were possible.
It seem you've done a lot of work on your gait algorithm - You mention that you have several version depending on the speed you want - I would like to make an algorithm that can switch between speeds on the fly kind of like a gearbox.

I would like to simply controls - to be able to use my cell phone & bluetooth to control the Hexapod - Just Forward/Back & Rotation - Sideway movement would have to be assigned to other keys. Turning while moving forward or back would have to change the turn radius according to the speed that is traveling. ( <---- This would look like a modification to the gait )

The algorithm to make it behave like a Pleo would be more complex
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Re: Hexapod V4b

Postby Matt Denton » Wed May 28, 2008 11:07 pm

ucaboys wrote:No problems here with the email notification.


great!

ucaboys wrote:I'll look forward to the kit. I would also like to help out with the software if that were possible.
It seem you've done a lot of work on your gait algorithm - You mention that you have several version depending on the speed you want - I would like to make an algorithm that can switch between speeds on the fly kind of like a gearbox.


Yes, my locomotion engine does allow dynamic gait changes, along with dynamic gait speed changes, both of which effect the hexapod speed.

ucaboys wrote:
I would like to simply controls - to be able to use my cell phone & bluetooth to control the Hexapod - Just Forward/Back & Rotation - Sideway movement would have to be assigned to other keys. Turning while moving forward or back would have to change the turn radius according to the speed that is traveling. ( <---- This would look like a modification to the gait )


It sounds like you need the p.Brain-ds24 + the dedicated hexapod engine which you will configure using terminal software and control via simple commands over a serial link. You should take a look at these threads:

http://www.hexapodrobot.com/forum/viewtopic.php?f=8&t=8

http://www.hexapodrobot.com/forum/viewtopic.php?f=16&t=14
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Re: Hexapod V4b

Postby ucaboys » Wed May 28, 2008 11:17 pm

Thanks Matt.

I've been looking at a Phoenix Hexapod Kit from Lynxmotion ( http://www.lynxmotion.com/Category.aspx?CategoryID=117 ) - but your design looks lighter, leaner and has better aesthetics & also seems to use less parts, could you confirm this for me. I'm really thinking of making a pet out of one of this. Similar to your iC - but with a bit more AI.
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Re: Hexapod V4b

Postby Matt Denton » Thu May 29, 2008 7:28 am

ucaboys wrote:Thanks Matt.

I've been looking at a Phoenix Hexapod Kit from Lynxmotion ( http://www.lynxmotion.com/Category.aspx?CategoryID=117 ) - but your design looks lighter, leaner and has better aesthetics & also seems to use less parts, could you confirm this for me. I'm really thinking of making a pet out of one of this. Similar to your iC - but with a bit more AI.


The Phoenix kit does have some roots from my V4b design, Zenta contacted me some time ago via youtube to tell me he had taken inspiration from my design, in particular the coxa. I did try to mention this on the Lynxmotion forum, but my post was deleted! :o So much for freedom of speech! Any who..

The kit design will be slightly different from the V4b design:

The Coxa design will not be as complicated as V4b.
The body will be slightly larger ( this is for practical purposes, and to take a standard sub-c cell battery pack ).
The body will not be a frame work like V4b, and more of a flat plate, this enables users to add holes to fit custom equipment.
The kit will use hitec type servos, 6 x HS-225MG & 12 x HS-645 servos or better.

There are several other things I need to sort out, such as weather to use nut & bolt to attach servos or snap rivets, and the surface finish is causing problems. Water cut aluminium is left with a slight burr, in order to remove this it is common practice to rumble the parts which removes the burrs, but also takes the shine from the aluminium. I have a sample that I will post a picture of soon, I will also try anodising the rumbled parts to see if this improves their appearance.
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Re: Hexapod V4b

Postby ucaboys » Thu May 29, 2008 4:20 pm

Personally I would be more interested in the framework version because of its elegant look, while also preserving the coax since this is one of the features that make this design unique.

As for the finish on the Aluminum - I think the burr can be concealed by either sand blasting the parts with a fine medium or by using a random orbit sander with a fine grained paper. I think you can anodize after sandblasting the pieces though - I'll ask the shops around here.

Matt do you have Skype?
I would like tell you about my project.
Your feedback would be much appreciated.

My account on Skype is l.garcia.79
Last edited by ucaboys on Thu May 29, 2008 5:33 pm, edited 1 time in total.
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Re: Hexapod V4b

Postby Matt Denton » Thu May 29, 2008 5:21 pm

ucaboys wrote:Personally I would be more interested in the framework version because of it elegant look, while also preserving the coax since this i s one of the features that make this design unique.

As for the finish on the Aluminum - I think the burr can be concealed by either sand blasting the parts with a fine medium or by using a random orbit sander with a fine grained paper. I think you can anodize after sandblasting the pieces though - I'll ask the shops around here.

Matt do you have Skype?
I would like tell you about my project.
Your feedback would be much appreciated.

My account on Skype is l.garcia.79


Hi,

If you haven't already seen it, you should take a look at the new post here: http://www.hexapodrobot.com/forum/viewtopic.php?f=5&t=33&p=78#p78

I think the coxa will remain the simpler design, as this gives more room for electronics and battery. I do have a rumbled aluminium sample which I will post a picture of soon, however, I need to take it to the anodizer to see how it turns out.

Can you post about your project in the projects forum?
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Re: Hexapod V4b

Postby paulp » Thu May 29, 2008 11:33 pm

ucaboys wrote:Personally I would be more interested in the framework version because of its elegant look, while also preserving the coxa since this is one of the features that make this design unique.


Here here...
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