Lynxmotion Tech Support

I did a bit of tinkering with strut configurations last night and decided to jump right in and go with a 3DOF plus steering setup. I'm going to try a dual ASB-11 setup between the "knee" and "tibia" joints rather than using "C" brackets there or a "C" and ASB-11 setup. Next week, I should have the rest of the brackets and tubing to complete construction of two of these hybrid legs. I think I have enough servos to fill two of these assemblies, and at present am planning to use HS-645's in the two heavy lifting joints and HS-475's for horizontal movement and wheel steering.

If this all comes together the way I hope, WALTER will be in a two wheel plus caster setup. In this setup, the strut/legs will be added on the chassis points each side of rear center and the caster will be on the front center point. I also have an HS-475 installed on the front center point for a pan/tilt sensor platform with a Sharp IR and PING sensor.

As for motor controllers, I am planning to try out two of the RoboClaw 2x5A controllers which can be operated from a single UART and has dual quadrature motor decoders built in. Hopefully I will be able to get two of these next month. In the meantime, just to get things running, I'll fall back to my Sabertooth 2x5 just for motion and possibly use the Webbot routines for quadrature decoding.

I just have not chosen the wheels and hubs yet, but am hoping to start out with the ARW-01 wheels and an appropriate hub.

As for controllers, I will bring my Society of Robotics AXON (Atmega640 based) into service. It has 3 additional UARTs in addition to one dedicated to USB. I will use one UART for an SSC-32, one for motor controllers, and one for XBee wireless. It's too bad the AXON has all but 16 I/Os wired for direct battery power. Only 16 I/Os (analog and digitial capable) are wired for 5V use. For now, the AXON has the I/O and memory (64K flash) I need to do what I want to do with WALTER. I've already got the AXON working with Sharp IR and PING sensors and, thanks to the Webbot library, things are quite easy to do.

8-Dale

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OK, I have done it! I just put in an order for all the brackets and tubing I will need to construct all four leg/struts (3DOF plus steering for each wheel) and some wheels (2 78" diameter x 0.8" wide orange banebot) and hubs. Assuming for now that I have at least 4 good HS-645 and 6 good HS-475 servos, everything should come together nicely as far as hardware goes. Next week I will have all the parts to build two complete strut/leg assemblies with motors, encoders, and wheels. Shortly after I have all the parts and assemble everything, I will be able to take and post some pictures after I've done mechanical calibration and selected the appropriate center points for each joint.

WALTER will be a two deck robot to start out, using the original two wheel bottom deck with front pan servo and caster already installed. As with earlier versions of WALTER, there will be a 7.2V @ 2800 mAH pack for the motors. I'll temporarily be using a 6V @ 1600 mAH pack for servos and electronics, but may use a separate supply for the electroncs. Motors will be temporarily controlled by my trusty Sabertooth 2x5.

Time to take inventory on my servos and select the ones to be used!

8-Dale

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I can usually handle complexity. It's the simple things that always confound me..
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Well, it turns out that I do not have enough servos to fill even just two of the struts/legs I want to put on WALTER. However, I can still get him two wheeling (rear wheel positions instead of centered), and then four wheeling. This only requires four ASB-24 brackets mounted on the points left and right of rear and center. I should be able to use HS-475 servos for steering the wheels. QME-01 Encoders will be on the rear wheels and eventually on the front wheels also.

I figure a four wheeled rover with all wheel drive and independent four wheel steering should be very interesting to work with. I should also be able to tinker with code for routines to do motions inspired by another robot for ASTRID. This is what WALTER is all about - tinkering with new things and code. Speaking of code, I have a basic layout of code for WALTER that I believe will work from a basic two and four wheel setup all the way up to the 3DOF strut/leg and steerable wheel layout. If I do the coding right, I should not have to recode too much (if any at all) for the various configurations. I've also allowed for up to eight PING and 8 Sharp IR sensors.

I'll have the new wheels and hubs this Friday (tomorrow) and the rest of the brackets I need next Tuesday. I already have the four ASB-24 brackets mounted for the steering servos now, and next is adding the second deck with enough space to allow for a dual sensor pan/tilt at the front point.

Yes, I will be taking and posting pictures as things progress with WALTER, now that I have a nice new Logitech webcam. There should not be any complaints about my new pictures.

8-Dale

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I can usually handle complexity. It's the simple things that always confound me..
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I now have the new wheels/hubs and just received my latest box of goodies from Lynxmotion.

I have all the steering servos (HS-475) installed now and have verified the new wheels will give the clearance I want. I am sure glad I did not order smaller wheels! I was a little disappointed that the new hubs are made of plastic, but they seem to be quite sturdy so should work just fine. Now I just have to get a 1/16" allen wrench so I can manipulate the tiny set screws. I much prefer the Lynxmotion hubs, but they won't fit these Banebot wheels. It's possible I should have ordered the narrower wheels, but will see how these 0.8" wide wheels work on various surfaces soon. I'm anxious to get the back wheels installed and working so I can start working on new locomotion code.

My trusty Sabertooth 2x5 will control the rear motors. I'm going to try out the serial control modes of the Sabertooth, which I have never used. Since the Axon controller has three available serial ports, it makes sense to fully utilize them. Another reason for exploring the serial control modes (besides the fact I've never used this mode) is that the RoboClaw controller has built in quadrature decoders that can only be utilized in packet serial mode. I already have two motors with encoders installed for the rear wheels. I've already decided that the home position for the wheel steering will be with the motor shaft pointing directly out from end of the ASB-24, which will provide a full 180 degrees of steering motion.

I'm also assembling one full leg/strut (3DOF) to tinker with. I think I have enough servos left to fill one up, except maybe for the hip servo. I'm still playing with different ways to attach the hip to WALTER. Using an ASB-06 and an ASB-09 will probably provide the most strength.

Pictures soon! These new pictures are very clear, so all detail should be very visible. I'm very happy with this webcam.

8-Dale

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I can usually handle complexity. It's the simple things that always confound me..
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OK, here it goes finally - PICTURES!

Here is the top view of WALTER with a side view of two of the four legs I am assembling to eventually turn WALTER into a hybrid quadrapod.

Front view of WALTER with the top view of the same two leg assemblies.

Side view of WALTER

More to come! Only three attachments are allowed per post.

8-Dale

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More pictures!

These are all bottom views of WALTER, which also shows the independent steering of the wheels and the range of steering that's available.




8-Dale

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And, yet MORE pictures!

Here you can see a better view of one wheel with range of motion of steering.




8-Dale

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I can usually handle complexity. It's the simple things that always confound me..
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Last of the pictures!

One more view of the independent steering of the wheels

One of the legs, side view. I wish I had a longer offset bracket for the legs.

Same leg, top view

8-Dale

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I can usually handle complexity. It's the simple things that always confound me..
Open your mind, Read, Learn, Think, Apply..

looks really cool. Interesting SES config!

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Mike

The robotics nut.

Thanks!

I don't have the wheels properly secured to the motors yet. I really don't like the Banebot wheel securement method. The wheel is kept on the hub with a snap ring. I just found out today that allen wrenches are NOT the same as hex wrenches, and I only have allen wrenches. There seems to be some confusion with retailers on the difference also. I do like the Banebot wheels, but don't care for the set screws used in the hubs. I wonder if I might be able to find a compatible 1/16" set screw for allen style head for these hubs.

I took a trip to my local hobby shop yesterday and they carry some nice wheels in various sizes that mount onto a 12mm hex hub, which should be compatible with the HUB-12 as far as I can tell. I will probably end up going this route for WALTER because I have a much wider selection of wheels and it will be much easier to deal with them. I found three one piece (wheel + tire) sets in three different sizes at the hobby shop, and they have larger sizes for the 12mm hex hub also, all the way up to almost 7" diameter. The wheels I looked at seem quite light also, and have the type of tread pattern I am looking for.

On the SES leg design, my goal is to keep the retracted leg as close to the body as possible and still get a good range of movement for my application. I'd rather have a longer offset bracket though, but I think this is a decent compromise. The only problem is I think I am going to have to go with 5980 or 5990 servos for at least one joint, and probably two joints, in order to be able to lift the full weight of the motor and wheel at the end. I have already proven that using all HS-645 servos will not do the job in the main lifting joint. I'm going to experiment with another possibility of using two 645's in a double jointed lifting arrangement, but I would rather not add another joint if possible. Using two 645's would be the same price as a single 5980 and not far from the price of a 5990.

8-Dale

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I can usually handle complexity. It's the simple things that always confound me..
Open your mind, Read, Learn, Think, Apply..

I've been working on some code for WALTER and the AXON controller. I've got the initialization code in and am starting to write code to actually do things. I'm using the Webbot avr framework, which makes it pretty easy to get things done. There is already good support for a lot of different sensors.

Anyway, attached are the .C and .H files of what I have right now. I'll be using this same basic code for A.S.T.R.I.D., but will be handling many more servos there.

8-Dale

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I can usually handle complexity. It's the simple things that always confound me..
Open your mind, Read, Learn, Think, Apply..

I've designed a small 3DOF arm for the front point which will have two sensors (PING and Sharp IR) and a camera. I want to use the BlackFin camera here, so will have to see how easy it will be to mount on the top of the ASB-18. The sensors will be mounted on the underside of the ASB-18 to allow the camera to be mounted on top of it.

Here are a few pictures:





8-Dale

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I can usually handle complexity. It's the simple things that always confound me..
Open your mind, Read, Learn, Think, Apply..

Mount the Blackfin camera on the ASB-18? (I'm currently working on a tilt/pan for the Blackfin). The Blackfin has 4 holes in the PCB, two on one end match up (pretty close) with two of the holes of an ASB-04. the other two holes of the Blackfin kinda hang over A plate with matching holes to the Blackfin camera (actually, the servo/radio board that the camera board mounts on) could be used on an ASB-04 to "pick up" the other two holes (via spacers) of the package. I like aluminum, but PCB stock should work fine for this, and allow the Blackfin to be mounted down close on the ASB-04.

Would that work for you?

Although looking at your camera bracket again, I see that the ASB-04 might be 90 out of the orientation you would need. I need to see my current experimental setup to know for sure...

Edit:

Current available Blackfin tilt/pan:



breakout board:



You can see the four mounting holes, and correlate a pair of holes to the holes on the ASB-04. Hole pattern might be 1.872" x 2.173" (not verified).

Alan KM6VV

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I don't think this would work for what I want to do. Remember, I want to have two sensors on the arm also. My idea is to secure the camera to the top of the ASB-18 with some insulator between and mount the two sensors on the underside.


I won't be able to mount the camera direct to an ASB-04. I think once I mount the two sensors and take some more pictures, it will be much more clear what I have in mind.

8-Dale

_________________
I can usually handle complexity. It's the simple things that always confound me..
Open your mind, Read, Learn, Think, Apply..

As I work on leg designs for ASTRID, I am also working on the eventual self leveling system for WALTER. In fact, part of the new leg design for ASTRID will be used for WALTER - just the second and third joints to make a 2DOF leveler. Even if this leg style isn't used for ASTRID at all, I will use this part of it for the levelers on WALTER because it is simple and will just work. It will be strong and not have any problem lifting WALTER's body.

Here is what I will use on WALTER:

I won't be installing these right away because there is still quite a lot to do before this. I want to have plenty of time to work out the steering patterns for the 2WD and 4WD styles before I add the leveling system, which will also require an accelerometer.

8-Dale

_________________
I can usually handle complexity. It's the simple things that always confound me..
Open your mind, Read, Learn, Think, Apply..