Halloween Hex

[Duane Degn]

Halloween Hex

I started this robot over a year ago. I had hoped to have it ready for Halloween last year but that didn't happen. I've had it walking around earlier this year but right now it's not working. I need to get it up and running so it can perform it duty of delivering candy to trick-or-treaters on Halloween.


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The frame was purchased from ebay for $93. I had previously purchased the servos from HobbyKing.

When I started working on this robot, several of my friends had either started or finished a hexapod. Bajdi had his Bajdupod 996R and Bill Henning had started work on his hexapod.

This wasn't my first hexapod. I had previously built a hexapod with Popsicle sticks. The Popsicle stick robot was a fantastic failure but I reused the servos in a small hexapod built from a kit provided by Paul K.. This "Mini Hexapod" worked well.

I used a Propeller QuickStart board as the controller for this robot. Since I was using two LED matrix "eyes" on the robot, the total number of servos was 22. I had previously controlled 32 servos with a QuickStart board so I knew the Propeller was capable of controlling all these servos.

As with the other robot article I've posted on Robot Rebels, I'm going to use the first six replies for additional information about the robot.

Top Post. Overview, table of contents.
Reply Numbers and Content of Reply (These replies will be filled in with detail in the near future.)
#1. Videos of the robot.
#2. Bill of material.
#3. Details about parts and build process.
#4. Description of software used by the robot.
#5. Plans for the future.
#6. One spare post.

[Duane Degn]

Videos

Here's a video showing the eyes working.

This next one is an earlier video. The eyes didn't work yet and the angle to pulse conversion factors I used were wrong. These erroneous conversion factors caused the robot to "buck" like a "bucking bronco." I kind of thought it looked cool. (The bucking is strongest at about 1:45.)

Hopefully I'll have video of the hexapod serving candy this Halloween.

[Duane Degn]

Bill of Material

1 x Hexapod Hardware Set from eBay (Mine cost $93 and included metal servo horns and bearing.)
2 x 15 Amp Switch Voltage Regulators
18 x HexTroinik HX12K Servos from HobbyKing
72 x M3 x .5 x 5mm Pan Head Machine Screws (2 bags)
12 x M3 x .5 x 6mm Pan Head Machine Screws (1 bag)
72 x M3 x .5 x 8mm Pan Head Machine Screws (2 bags)
2 x Bags of M3 x .5 Nuts
6 x M3 x .5 x 12mm Pan Head Machine Screws (1 bag)
1 x Bag of M3 Washers
2 x Custom PCBs for attaching servos (gerber files linked here)
2 x Pan/Tilt Gizmos (on eBay and other sites, don't pay more than $3 each)
4 x HXT900 9g Servos
2 x 8x8 LED Array with MAX1972 Driver
1 x Wireless Wii Nunchuck
1 x WiiChuck Adapter

[Duane Degn]

Build Process

I kit I purchased came with a lot of nuts and bolts but the nuts and bolts were the wrong size.


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My parts looked a lot like the parts Badji used. (The photo below was borrowed from Bajdi's page.)


hexapod-chassis-kit.jpg (31.8 kB . 500x333 - viewed 1266 times)

IIRC, the kit Bajdi purchased didn't include the metal servo horns or the flanged ball bearings. My kit included these items but there wasn't any information on eBay about these parts. I just got lucky they were included. If it's possible, I suggest finding a seller which includes these parts. These parts are available from other sources.

The kit didn't include any instructions but from looking at pictures, I could kind of figure out how things were supposed to fit together. While I don't consider this post complete instructions on how to build these hexapod kits, hopefully the photos will provide some hints to anyone interested.

Remember to build three left and three right legs. The six legs shouldn't all be the same. Three are the mirror image of the other three.

Here are the parts I used to instal the flanged bearing.


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I used a washer prior to adding the bearing.


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I used two nuts to hold keep the bearing in place.


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Gordon McComb suggested I use washers with nylon inserts instead of two nuts. If I were to build something like this again, I'd likely take Gordon't advice and use nuts with nylon inserts.

The second bracket of the leg needs to be attached to this bracket with the flanged bearing. The machine screws need to be the just the right length to pass through the holes in the two brackets but not so long as to interfere with servos used in the brackets. I think these machine screws are 6mm long. IIRC, there isn't room for a washer.


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Here are a couple of pictures of these two brackets joined together.


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This next photo shows the brackets after the servos have been added. As you can see, there's not much room to spare.


FlangedBearingMount140920j.jpg (163.75 kB . 743x584 - viewed 849 times)

Here's a picture showing the leg attached to the frame. My kit included three long standoffs. Two of these standoffs are visible in the photo. I think it would probably be wise to use four standoffs instead of three. The dimensions of the brackets and the servos will determine how much space there is between the top and bottom frame plates. The standoffs were just a bit too short of span this space so I added a few washers to make up for the gap between the standoff and frame.


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Here are a few pictures of the completed frame with the legs attached. I used a Dr. Pepper can to provide scale.


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HalloweenHex140920a.jpg (196.53 kB . 786x595 - viewed 927 times)

With the hardware from ebay put together, I could start figuring out how I was going to get control signals and power to all those servos. This part of the build will depend a lot on what sort of controller is being used. While there are likely lots of "right" ways to wire up a hexapod, I think there are even more "wrong" ways to do so.

I had originally planned on making my own PCB to use as a controller for this robot. Unfortunately I had a major mistake on the board and it ended up being pretty useless for this application.

Last year while building this robot, Radio Shack was clearing out a lot of their inventory and many people were able to find Propeller QuickStart boards for very low prices. I didn't find any of these inexpensive QuickStart boards myself but I had a pretty good supply of QuickStart boards from back when they were sold for $20. I thought I'd use a QuickStart board to show others, who had one, how useful they could be.

If any of you are interested in trying out the Propeller, the Propeller Project Board is probably the best bang for the buck right now.

I had previously tried several methods of adding servos to a QuickStart board. Here's a board I made from perf board for adding servos to a QuickStart board.


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ServoExtension140925b.jpg (172.09 kB . 710x699 - viewed 834 times)

I think I used the boards above with my Popsicle stick hexapod. I think I'm using the same QuickStart board in this robot as I had used in the Popsicle stick robot. The ribbon cable in used in the above board wasn't long enough for my needs with this Halloween Hex so I made a few more boards.


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ServoExtension141008a.jpg (159.82 kB . 780x560 - viewed 827 times)

I had these three boards made at OSHPark. Each board could connect to ten servos. I used two of these boards on this hexapod.

I like using these IDCs (insulation displacement connector) when possible since they're so easy to add. I could use solid rows of male headers when using the IDCs. There had to be gaps in the pins to allow room for the extra plastic around the female sockets. I used a small piece of perfboard to add male connectors to the I/O pins numbered P10 through P13. These pins were used to control the LED matrices used for the eyes and one of the four pan/tilt servos.


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Here's a closeup of the small perfboard.


HexTop151010b.jpg (194.86 kB . 678x441 - viewed 814 times)

I used some Polymorph to make the bottom sides of the small servo adapters nice and smooth and added Command Strips (kind of like Velcro) to both the bottom of the small PCBs and to the ePVC platform.

I'd heard a bunch of horror stories about voltage regulators burning out from attempting to power these sorts of hexapods. I didn't want suffer similar frustrations of servos not receiving enough power so I used a two beefy regulators. I don't know if both regulators are needed of not. I should probably experiment and see how well the robot works with just one regulator but for now, I'm using both regulators.

Here are a couple of pictures showing this top platform with the gimbals for the eyes added.


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HexTop141030b.jpg (212.75 kB . 843x630 - viewed 800 times)

[Duane Degn]

Reserved for Notes about Software

I'm not sure if I'll be releasing the software for this robot but I'll add some comments about the IK equations I used.

[Duane Degn]

Reserved for Future Plans

[Duane Degn]

Reserved 6 of 6.

[craighissett]

I love this hexapod - I hope you get it up and walking soon!
Love the idea of reserving the posts for expansion too.

[erco]

Awesome bot, Duane. Pressure's on though to finish. Halloween will be here before you know it!

[Duane Degn]

I found a major problem with the hex. I think I had plugged the wireless Nunchuck receiver in upside down.


WirelessNunchuckRx151009a.jpg (32.64 kB . 286x264 - viewed 1101 times)

The USB port jumped from 0.1A to 1.1A when the receiver would connected.

I opened up the receiver to see what was inside.


WirelessNunchuckRx151009b.jpg (47.29 kB . 413x269 - viewed 797 times)

There were two PCBs on top of each other. I pulled the PCBs apart a bit before taking the photo above. I don't think the receiver is repairable.

I have another wireless Nunchuck. I'll need to make sure and come up with a way of not plugging in the receiver upside down.

[erco]

Dangit that sucks! Of course we'll bump Halloween back a few days to accommodate this setback learning opportunity.

"Experience is what you get when you didn't get what you wanted."

I speak from experience.

[Bajdi]

Yours walks much better then my similar big hexapod. Makes me want to reprogram mine

[ptp]

Duane,

What kind of battery do you use. If i power mine with 2S cells, do you think the servos can accept 7.4v without risk of damage ?

Thanks.

[MEgg]

Duane, where did you buy the 2 converters?

[Duane Degn]

Duane, where did you buy the 2 converters?

I purchased several of big voltage regulators from various sources. There's a link to the ICStation source in reply #2 above. I also purchased at least one of the regulators from a seller on ebay.

The regulators have worked fine so far but I haven't tested how much current they can really handle. I'm not convinced these regulators are the best option but they appear to be at least an "okay" option.