Loki, a simple, small biped

Lynxmotion Legged Robots
21

Hi,

Loki is now able to walk forward or backward!

I’ve now got a parser for simple commands like the SSC32 and SEQ uses. I can command from the Docklight terminal emulator, or from SEQ. Docklight allows making up command sequences that can be sent with the press of a button. Handy!

I can also play back sequences that I have coded into the source code by issuing a “sequence” command… They are basically the sequences that I developed in SEQ. I “cut and paste” them into simple character strings. The sequences are the forward and reverse of a single step cycle (gait) , about 6 steps.

It was a little slow going to get 6 steps for a single cycle of a gait, but I’ve not gotten much past that.

It looks like I’ve got servo “offset” errors (from null) that I should determine and put in a table for use. Then perhaps a simple set of positions will define a step cycle. From there, can I add or subtract to the leg advances to give me a turning rate to the gait? I’m not sure what direction I should take (no pun intended) at this point. Comments?

I’m a little weak on the knee servos, so the 6-cell battery is on a tether. LM has a 6V NI-MH 1600 mAh battery pack that is reported to be 1/2 the weight of my old (7.2V) Nicad battery pack. This might be light enough for Loki; otherwise I’ll need to put on some stronger servos.

I got a kick out of an old “Stargate SG1” episode last night; they had Loki as a bad alien (Asgard) scientist! I knew I’d heard the name before!

No videos yet!

Alan KM6VV

22

Loki is a Norse god…

23

I knew that!

Actually, I’m considering Sigyn, the wife of Loki, as the new name of my 'bot.

Alan KM6VV

24

actually Loki was the norse god of mischief so depending on the intent of your 'bot it may or may not be appropriate. 8)

25

Hi Alan!

Great to hear that Loki is walking, any pics of the new legs? Smart thing about using the seq’s you made in SEQ and “copy&paste” them into your code.

26

Hi Kåre!

No new pics, I kinda cheated. I had some scrap 1.25" x .5" pieces of PCB from cutouts. I bolted these “foot extensions” onto Loki’s feet. That was enough to allow the 'Bot to walk.

I figured it would be a good idea to see what was needed before I committed to using up more of that expensive PCB stock. ;>)

I’m now debating whether or not to give Loki his own “learn” function. I can “inch” a leg up until they’re in the desired position; I’d just need to add a save/load of the on-chip EEPROM. Or I could add a 24L256 I2C EEPROM as well.

But I’m not really interested in sequences as much as I am in developing a gait engine for Loki.

Alan KM6VV

27

Hi to the forum.

My Loki now has some primitive save,view,edit and execute commands for developing sequences in EEPROM. I can position the 4 servos, and save them into a sequence. The sequence can be stepped through forward and backward, and re-edited to develop simple motions or gaits.

I discovered that a simple 6 or 7 step sequence that describes a gait cycle can be called repeatedly to allow Loki to walk. The sequence can be run backwards as well. For turns, two additional short sequences give left and right turns. Then it’s on to postures. After the sequences are developed, they can be “viewed”, which allows them to be “copied and pasted” into the C code, and called up by specifying a sequence number. Behaviors can then call these sequences to animate Loki.

I’ve added the SRF08 ultrasonic ranging module, although it needs a bracket to hold it properly. This sensor should allow triggering the behaviors. The AFSM SRF08 I2C code developed does not use interrupts, and does not “block” waiting for the many responses from the I2C hardware (in PIC).

I’ve taken another look at the Brat! Watching and developing a gait for Loki has given me a new appreciation for the Brat. I have some additional Futaba S3004 servos (44 oz/in), and I’m wondering if they would be powerful enough to run a Brat? Loki needs bigger knee servos then the Futaba.

Dale, did you say that you developed software to run your new Brat? I’m wondering what others have used to develop sequences?

Alan KM6VV

28

Any videos or new photos of Loki walking?
The pcb idea is great. Nice to see that you have made so much progress.

29

Hi Tolisn,

Sorry, not yet! I need to borrow a video camera. I don’t think my old Sony Beta from 20 years ago is going to be good enough. I could record in VHS, but then I’ll still need a way to xfer to a MOV or whatever file. Hopefully I can get my youngest son do do it for me!

Alan KM6VV

30

Some pix of the parts for the new (longer) feet.

http://www.marconettengineering.com/LokiLegSet2b.jpg

Layout on paper:

http://www.marconettengineering.com/LokiLegSet4b.jpg

A template used to make the center holes on walter:

http://www.marconettengineering.com/WalterTemplate1b.jpg

Loki now walks with it’s own gait. Sensors have been added, and a BlueTooth link for telemetry. More pix to follow.

Alan KM6VV

31

This might make a good intermediate robot kit… :smiley: I am thinking, pair Loki with the new SSC-NG board that is being developed and program it in C.

Very nice work, Alan! I wouldn’t have expected less after seeing the great work you did on the new decks for W.A.L.T.E.R. :wink:

8-Dale

32

Thanks, That’s kinda what I was thinking. I’ve already laid out another “body” (the flat PCB sheet that holds the top two servos and the controller PCB) to take a Dontronics DT106 board, although an ABB board or your SSC-NG board would also fit. These boards are not as wide, and thus I can re-use the 1st set of feet I made with a new “slimmer” body (the feet have to “cross” to be able to swing the body up).

Who’s interested?

Alan KM6VV

33

I don’t know. :wink: I am interested in the whole kitting idea though. I have some ideas of my own.

8-Dale

34

Posting some general dimentions would be of interest for making the parts from plywood (although a CIA type should get pretty close looking at the pix). I went by Lowes this afternoon and sheets of the 5.2mm Luan plywood are still pretty inexpensive. 2’x2’ sheet for $2.20, 2’x4’ for $3.99. A coping saw to cut the pieces is $7.99.

35

The parts should not be too hard to cut out. I have generated JPG files from my cad drawings. One should be able to print them out full size, adjusting the scale until the dimensions are accurate. Then they should be able to attach the prints to the wood or PCB stock, and cut them out.

Of course, it’s not necessary to make the parts exactly correct. I actually drew my parts from viewing pictures of David Buckley’s original Loki. I got the basic sizes of the feet, the width, and the height of Loki. I worked from there to design my own parts.

Loki Body:
http://www.marconettengineering.com/LokiBody2.jpg

Loki Foot parts:
http://www.marconettengineering.com/LokiFeet.jpg

There are tabs and notches that fit together. Most of the larger holes are for appearance, and not needed.

HS-475 servos should be used for the knee servos, smaller ones will work for the hips.

Loki will be seen to be about 6.5" wide, 5" high, and a little over 5" deep. The feet come out to about 5" deep, and 4" wide.

Loki with ultrasonic an IR sensors, BlueTooth:

Loki updated, added sensors on a pair of 2nd deck plates:
http://www.marconettengineering.com/LokiUpdate3b.jpg

Loki updated, the Bluetooth antenna makes a tail!:
http://www.marconettengineering.com/LokiUpdate5b.jpg

Note: Battery goes below the controller PCB, and is not installed.

Additional questions, just ask!

Alan KM6VV

36

Here’s an interesting article on using the Sherline CNC mill to cut robot parts.

botmag.com/articles/sherline.shtml

I’ve got to get busy!

Alan KM6VV

37

An update to Loki’s story. I received this email on the HBRC list:

Thanks for breaking the news Wayne!

Alan KM6VV

servomagazine.com/preview.php?issue=62

38

Congratz Alan!

Front page! 8)
(Sorry for missing some of your posts, I have not paid attention to the Biped section :blush: )
Your Loki looks awesome, very nice work!

It would be cool to see Loki walk. With its wider feet you have solved the balance issue :wink:

Ahh, I wish I had a CNC machine… Your custom parts looks great. Smart move to use PCB and soldering the parts together.

39

Hi KÃ¥re,

Thanks! I need to get some video’s made. I don’t think too many others are reading the Biped section either.

CNC IS great for for these projects. I am pleased that the PCB stock worked so well. I may use it in the next project.

And now I’ve got some funding for my next project!

Alan KM6VV

40

Congratulations to LOKI for making it to the front cover of SERVO magazine.
You guys are unbelievable.