Wednesday, December 22, 2004

New Head Design for Knewt #2


Stuart's head design
Keith Rowell Design

Stuart sent this head design last week. It was designed in SolidWorks and exported in the SAT format first. This format didn't work for import into IronCAD so we tried it next as a Parasolid which IronCAD liked just fine.

Stuart's abilities with CAM as well as the design software shows the kind of skill and talent he possesses. Expect to see these two versions and maybe more, chicken walking around all over the place come this summer.

Stronger Servos for the Foot Motor


42oz/in foot motor 01
Keith Rowell Design

There was some concern from the beginning as to whether the feather weight servos would suffice for the foot motor, because it's the only motor that experiences the full weight of the robot during walking. The HighTek HS-55 feather servos are rated at 18 0z/in at 6V. http://www.servocity.com/html/hs-55_sub-micro.html Over powering might take it up to a higher torque, just before the magic smoke escapes.

Phillip FitzSimmons did a rough estimate of the forces needed to hold the weight of the bot on one motor and surmised that 15-18 oz/in wouldn't be enough. Not being able to find any servos in the same size format that had more torque, I ordered the next larger size. http://www.servocity.com/html/hs-81_micro.html An even stronger one is available in the same size format: http://www.servocity.com/html/hs-85bb__mighty_micro.html And one with metal gears: http://www.servocity.com/html/hs-85mg__mighty_micro.html

48pitch gears are available for this servo spline shaft too. I ordered a 18tooth pinion and 66tooth spur that will replace the ring and pinion used on the smaller motor. http://www.rcmodels.com/1002-9524.html http://www.robinsonracing.com/catalog/catalog.html
An 18 and a 66.
http://www.servocity.com/html/48_pitch_servo_gears.html
Metal ones are available
http://www.servocity.com/html/48p___32p_metal_servo_gears.html
http://www.servocity.com/html/48p_aluminum_hub_gears.html

The smaller motor with it's smaller spine shaft required a tricky manuver to make the pinion fit. And it requires a pillow block to hold the pinion in place. The larger motor is much easier to fit because of these issues. I would still like to be pleseantly suprised to see the smaller motors carry the day. But I'm planning their replacement just in case they don't.

I'm also looking for travel cases for the knewt. It's overall size is 7x9x12". The pelican water tight case is ideal with the foam inserts but is expensive at over $100. http://www.all-pelican-cases-4-less.com/detail_pelican_1600.html If anyone has access to travel cases for lot less, please let me know.

42oz/in foot motort 02
Keith Rowell Design

42oz/in foot motor 03
Keith Rowell Design

Wednesday, December 15, 2004

Head and Shoulder Plates Finnished


shoulder plate and head plate with head turn motor atached B
Keith Rowell Design

Stuart has finnished the first shoulder plate, a very complex part to make as we mentioned last week. All of the weight of the bot is carried through the big bearing, and then to the legs, through this plate. It's un believeably light.

The head plate holds the head onto the neck using the same large size bearing. The servo is responsible for the head turning movement via a mechanical connection with the servo horn, through the center of the bearing.

I don't anticipate getting a new camera for Christmas, so WYSIWYG.

shoulder plate and head plate with motor attached A
Keith Rowell Design

In this orientation, we are seeing the top of the "right" shoulder plate. And the top of the head plate/mtr. Stuart did a fantastic job on these parts and we hope to get a movie of the cutting process this week. It's very exciting to see these parts in the "physical" world.

Mojo Mods


testing mojo board with leg
Keith Rowell Design


We've recieved the second ServoMojo board and are modifying our set up routine. Until now we were setting all the motor presets with a terminal program directly to the Mojo, and running a pic grogram to control the Mojo afterward. Bob's plan now is to do all the communication with the Mojo through the pic using a "passthru" scheme for testing, and adding a "setup routine" in the pic code to initialize the Mojo on start up.

The Mojo has the set-up saving features that store servo acceleration, speed, trim, etc. But reading, checking, resetting, these from the controller is a step above the manual procedures we've used so far. Brian Dean of BDMicro has been very helpfull as we learn the in's and out's of the Mojo board. Thanks Brian again for your assistance.

Thursday, December 02, 2004


shoulder plate physical
Keith Rowell Design

shoulder plate model
Keith Rowell Design

Shoulder Plate Progress


shoulder plate progress

Stuart has begun the really complex parts and I was lucky enough to get photos this week. This shoulder blade part is about 2/3 complete. It started out almost 3/4" thick. The steps used to make this part were 3 setups so far. Stuart set the CNC up for a cut from the "end", using that surface to set up the tools. Then he set up again for one side and cut away the bulk. Then, set up on the other side and cut the holes. It's a very big deal to figure out how you're going to hold the part for cutting. And the surface that you use to touch off the tools for setting up the CNC must be perpendicular so that the various setups will be "synchronized" or the part will have misalignments in assembly. It's quite a complex part. These photos are a disappointment but you can see which part it is by comparing to the model.

shoulder bracket
Keith Rowell Design

shoulder bracket
Keith Rowell Design

First Leg Assembly


leg assembly
Keith Rowell Design

This leg assembly has been togeather since before the holiday but I only got a photo today. We've had the leg and foot parts for some time, it was the ankle hinge parts that completed the assembly to this impressive point. Tape is holding it in a standing position.

Ankle Hinges


Ankle Hinges
Keith Rowell Design

Stuart made these the week before Thanksgiving. They're very nice and use welding rods for hinge pins. See them in use in the leg assembly above.