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Baranyk
04-17-2012, 08:35 AM
Good Morning (or evening, TZ dependent) Everyone,

First of all, I've been hanging around without a login for sometime to see what the community is like here, and I'm happy to report I like it... which may or may not be good for you :o

I'm thinking about building a quad for the competition, and I do have a couple design questions:
1. I noted that Issydunyet utilized several Lynxmotion brackets and parts, however upon importing them into Inventor they did not appear to couple well (out of the box) with the brackets provided for the AX-12 servos. Can someone confirm that they do, or am I sadly mistaken?

2. I'm planning on building a more spider-like design (ie, longer legs) for the quad, utilizing the longer aluminum tubing from Lynxmotion because I feel it will give me more flexibility in positioning and gait. I was wondering if this has been tried before, and if so, why we appear to have moved toward a more crab-like form factor (I haven't been able to find an example here yet of what I am talking about... CAD images to come) Addendum: Imagine a daddy-long-legs spider.

3. What are the limitations on the AX-12 servos? I know without drawings and designs this is hard to answer, but if I could get a roundabout weight for the chassis and body I can figure things out from there.

4. Am I going to have to learn Python? I'm extremely comfortable with C++, C#, and reasonable with Java. I've used Python before, but if at all possible I was going to use PyPose/NUKE to generate the initial program and then begin to hack at that in C... is this reasonable or am I going to spend 3 months making one movement in C that would take 3 days in Python?

5. Control: I just need to get this out of my system, even though I'm sure the answer is obvious: Arbotix, Battery, x2 XBee, battery (11.1 V), servos, frame, and IP camera are all I need to start, right? The Arbotix handles all the servo controls?

6. If you hit this question, then say so and if you're of age and I ever make it to competition I owe you a beer (or root beer, if you don't drink (or glass of milk if you don't drink soda/pop)).

7. You now have the opportunity to help somebody build their workshop from the ground up. List off your favorite tools for your tinkerer's haven, and where I can find something reasonably priced to match.

That's all for now. I work full time during the week, so we'll see how much time I have to update and work on this. But thanks for paying attention, and the help in advance!

EnderWiggins
04-17-2012, 11:48 AM
1. I’ve never tried this but Solidworks does show a small difference between centers in the mounting holes of the Lynxmotion and Robotis brackets. The difference is not huge though so you could probably just ream out the holes on one of the brackets and make sure to use 4 screws to keep the parts aligned. It wouldn’t be an ideal situation but it would probably work. Just make sure to tighten the screws down well and do it in a star pattern like car tires if you’re really worried. ^_^

2. There are a lot of reasons for not using longer legs on walkers. The most common reason is lack of servo power; whenever you increase the length of a linkage between a motor and its load you get a linear growth in the required amount of power to accomplish the movement. For example if you attached a 10 kg load 1 cm from the output shaft of an AX-12A you can generally expect it to turn (at slower than its no load speed of course). On the other hand if the linkage is 2 cm long it will most likely not move. Increasing the linkage length such that the geometry was to look at all similar to a daddy long legs would require a very long linkage and therefore a much stronger actuator.

Longer legs also introduce other problems that might not be so apparent like lose of rigidity. For example my first biped used Lynxmotion tubing in between servos in the legs to increase the length of the leg. When I designed it I expected that lack of servo power would cause it to be a failed design. However, it turned out that the loose fit of the tubing caused the largest problems. When you add together linkages in these robots if there is even a small amount of play between servo mountings and the linkages it will multiply with each additional linkage so that when you go to create a gait it’s like working with a robot made of wet noodles. This problem can arise in shorter legged robots too but increasing the length of linkages allows for more deformation in the linkage material which manifests itself in a similar way to the loose fittings.

3. Trossen Robotics’ PhantomX-AX-12 is about as large as I’d want to go on an AX12 quad. I’m sure there’s room to make it a bit larger but if you want to add things on top you’re going to have a hard time with it.
http://www.trossenrobotics.com/p/PhantomX-AX-12-Quadruped.aspx

The servos are great for building walkers so even if you tried your daddy long legs concept the worst that can happen is you have to redesign some parts. Try and make the design in a way that doesn't require a lot of modifications to change the lengths. You could use dowel rods (like Issy) between the servos and if you make the legs too long just trim down the length of the dowels. That way you can try different length legs and find your own sweet spot between looks and power.

4. Unfortunately, I don’t own an Arbotix but, it looks to me that the output of PyPose is C code. So not much work would be required at all.

5. Don’t forget weapons if you’re going for Mech Warfare! More importantly don’t forget a battery charger and extra batteries. It’ll increase the amount of fun you’ll have dramatically if you get enough battery charging units to keep a perpetual cycle of full batteries going.

For example, I have two chargers and each can charge 2 batteries at 2C (Warning: My batteries support charging at 2C but many lipo don’t and will explode if you do this.) My robot runs about 20 minutes continuously per battery so if I’m always charging 3 batteries I always have a fully charged one to replace the current drained one.


6. I’m of age and… I don’t always drink beer but when I do, I drink Dos Equis.

7. I just got a little table top CNC router that I’m currently enjoying. But, I haven’t had it long enough to say if it was a good buy. Personally if I had no tools I would buy a Dremel and nice soldering iron before anything else. If I listed my tools from most used to least it would look like this

a. Pliers, Screwdrivers, Hand Saws, Clamps ect…
(Everyone should have hand tools; power tools won’t be of any use if you haven’t developed the skill to use the equivalent hand tools first.)

b. Dremel (It can do anything given enough practice!)

c. Soldering Iron (Weller WES51, Just spend the money on a nice one up front… RadioShack $15 ones are worthless.)

d. Hot Glue Gun (Cover the end of every cable you make neatly (use wet fingertips to mold it, be a man. No pain No gain!) with hot glue and you’ll save yourself hours of debugging the magical “software” errors a loose cable creates.

e. Jig Saw

f. Drill + Large Set of Drill Bits

g. Cupcake CNC (If I could go back in time I would have built a Reprap I regret that decision a lot but, I’m poor and it gets the job done so I just printed out some upgrades and made do.)

h. CNC Router (I got this to cut brackets on, It can cut aluminum but the electronics suck majorly and should be replaced with something better like a gecko drive. Also it looks like they raised the price on it; if you want one put in a best offer of around 600-700 I bet they would still accept it.)
http://www.ebay.com/itm/CNC-3020-ROUTER-ENGRAVER-DRILLING-MILLING-MACHINE-m6-/370532768919?pt=LH_DefaultDomain_0&hash=item5645795c97

(http://www.ebay.com/itm/CNC-3020-ROUTER-ENGRAVER-DRILLING-MILLING-MACHINE-m6-/370532768919?pt=LH_DefaultDomain_0&hash=item5645795c97)
The above is just my experience so make sure to take it with a grain of salt. ^_^ If you happen to live in Florida and need a sparring partner for your future robot send me a PM!

Hope it’s okay this was my first post here!

tician
04-17-2012, 12:04 PM
1. Which version of Issy? There were atleast three, and the last version that looks like a lizard is made from AX-12/18's, dynamixel brackets, and custom rapid-prototyped plastic pieces. To the best of my knowledge, dynamixels cannot be mated to any frames other than those made specifically (or modified) for the dynamixels (and there are several different series of dynamixels each with different external dimensions and compatible frames).

2. Longer legs => higher torque => stronger servos => $$$$. See the EX-104+ Giger thread for an example of how expensive it can get. Higer torque servos also increase the weight of the bot which further increases the loading on the servos. There are passive designs like RoMeLa's Strider, but I have not really seen many smaller bots that did not use servos directly contained in the joint (versus actuating the joint via a cable or other mechanical linkage with the actuator located in the main body). I have certainly thought about making several with either cable linkage or pneumatic actuators for the joints, but I am not the best at finishing personal projects. Not to say any of it has not been done in some form. I am rather fond of DLR's little crawler (http://spectrum.ieee.org/automaton/robotics/industrial-robots/crawler-robot-on-the-loose-at-german-lab), but there are others like the jamming hexapod (http://spectrum.ieee.org/automaton/robotics/diy/jamming-robot-gripper-grows-some-legs) and this little quad (http://spectrum.ieee.org/automaton/robotics/robotics-software/video-sq1-quadruped-robot-from-south-korea).

3. Just read through the project threads, they tend to give a pretty good idea with the rough dimensions and loading. We have a number of Humanoids, Biped-walkers, and Gerwalks in the lab that all function pretty well on just two legs, so they are quite capable little servos (and painful if any digits get caught in any pinch points/joints).

4. PyPose and NUKE are just programs you use to create gaits and poses, no python programming needed (using python allows nigh-universal OS compatibility). All usage of the gaits and poses created by PyPose/NUKE are used in the C/C++ code on the controller of your choice (the NUKE output is mostly self-contained, but the fixed poses would require some modification to the BioloidCommander files if not using an AVR system - currently uses a special read required to pull the poses out of FLASH memory).

5. Indeed. Once a pose file or a nuke gait has been created, you simply add a small program for the arbotix to receive input from the XBee and perform actions using the functions in the ax12, BioloidCommander, and nuke files. There are examples in the arbotix google code svn repo as well as DB's example program here (http://forums.trossenrobotics.com/showthread.php?4405-Meet-Hi-No-Hikari/page15).

6. meh. I'm much better at giving than receiving. It's actually a bit of a compulsion to be helpful when possible and invisible/unobtrusive when I can't.

7. Depends on what you want to do. For electronics, a decent pair of wire strippers, wire cutters, and maybe a decent soldering iron (Hakko, Aoyue, and Weller are among the best, but there are plenty of decent generic versions of a certain Hakko model. I have a 50W Velleman station, but wish I had spent a little more than $20 for a much nicer station - faster heating, temperature dial controlled instead of yellow to red power/temperature control, and modular/replaceable handle). For surface-mount electronics (SMD or SMT), a hotplate or electric skillet tend to be adequate for low volume re-flow soldering. For metal frames, a hacksaw (or maybe a coping saw with metal cutting blades) and drill/dremel would be the bare minimum (maybe add a cheap nibbler tool and a vise). For more advanced stuff, a rapid-prototyper (RepRap, MakerBot, etc.) is a nice (if expensive) addition.

For easy professional quality sheet/plate metal work: a configurable tabletop/floor brake (easily and cleanly bending metal - configurable versions allow the removal of sections of the top half of the brake/clamp to make sheet metal boxes easily), corner-cutter (cuts a 90 degree internal corner), and drill press. These are all on my wish list for tools/equipment, but as-is my working for a largish educational institution allows me direct access to all these. For professional quality cuts, a CNC waterjet/laser/plasma cutter is a very expensive addition and mostly falls under the "who has a bigger...?" banner, as there are numerous online (and probably a few local) services that offer waterjet/laser cut metal for reasonable prices.

Baranyk
04-17-2012, 12:22 PM
Thanks for the help, both.


1. Which version of Issy?
The one used as the tutorial. He's using a pair of right angle brackets and aluminum tubing for the feet, and then in the Kinematics thread, he talks about having leg length problems. Being a Computer Engineer only a year out of college, I'm trying to keep my coding and math skills up to date at a job where they aren't used as much. So I'd be extremely interested in getting in on the IK action. Therefore, I'd like to try to keep hardware on the budget, and maximize my return on a minimum investment (I currently do technical marketing). Programming is free, hardware is the cost here :)

And I like quadropeds. We all have our personal favorites :)

List of tools needed so far:
Standard hand tools: No surprises here
Soldering Iron, Professional Grade (Tax returns, come quickly!)
Drill, again no surprises
Dremel, I've had need of this in the past, just had no idea what the name of it was :)

Gertlex
04-17-2012, 01:59 PM
I'll just address a few of points since a bunch has been answered already :)
1) I'd recommend just getting the Bioloid Frame Kit ($100). You can build the legs easily with this, and have lots of fasteners to start off with. Then use sheet plastics with holes to join the four legs together and form the body.

4) You listed what I think of as heavy-weight languages. Having a lighter-weight language in your toolbox is good for smaller stuff, and Python is great for this (plus, it's the easiest language to google for the syntax/docs that I've seen).

5) You'll also want to get a proper LiPo charger. Getting these off ebay is fine. (Titan B6 or Imax B6 are the commonly used chargers, I think)
That said, I only use python indirectly for my robot - namely for video display and HUD information on the computer.

7) I'll just add that for using a dremel, I highly highly recommend diamond cutting wheels (http://www.amazon.com/Anytime-INDUSTRIAL-DIAMOND-CUT-OFF-LAPIDARY/dp/B000FJN8LO/ref=sr_1_13?ie=UTF8&qid=1334688354&sr=8-13) and engraving bits (http://www.amazon.com/Pro-Quality-20-Piece-Diamond-Point-Rotary-Tool/dp/B000MOI9G6/ref=pd_sim_hi_5). The former don't break or wear down, and the later are just super useful (especially with working with the 2mm hardware for AX-12's; good for 2mm holes in plastic/carbon fiber, and also good for self-tapping holes in plastic for 2mm bolts).

7b) There's also raw materials to work with. Generally it's metals and plastics (and cardboard for prototyping). Sheet plastic, e.g. ABS, and delrin are great and easy to work with. Delrin costs more, but is more heat resistant (important in that it doesn't gunk up the engraving bits and drill bits). For non-load-bearing stuff, 0.03" polycarbonate is easy to drill, not going to break, and can be bent/formed by hand without heat (though heat helps, but I've not tried this). Carbon fiber is fun, but I'm not going to recommend it because its dust is not good for you. :)

7c) More on fasteners: Most of us use socket head bolts rather than phillips screw bolts. This is something you'll have to decide on, though, as the metric socket head bolts are a bit of an investment, and these robots have a few hundred bolts apiece. I've found nylon 4-40" bolts/nuts/standoffs/washers to be great to work with. They're light weight, not conductive, and generally good for mounting electronics. You can even cut the bolts to length without thread damage.

byi
04-17-2012, 03:47 PM
I found that I can build pretty much everything with a dremel, some basic hand tools, hot glue and an auto wire stripper. Only used a drill press once because it simplified chassis design a little bit. This probably is because I use bioloid brackets (which I highly recommend because they are extremely easy and reliable) and therefore only have to worry about complicated building on my turret. Of course, I only use so few tools because it's all I can get to. If you can get more powerful tools, you probably should of course. Things mostly work for me; it just looks less pretty. Just thought I'd mention that it's possible.

tician
04-17-2012, 09:45 PM
Dremel (or generic) rotary tools are all around very useful tools. If need be, you could make a dremel into a simple drill press or even stick one in some rapid prototypers instead of the extruder head to make a 3-axis CNC router.

Gertlex mentioned it for carbon fiber, but I would recommend you always wear a mask when grinding or sanding. Some materials are more potentially harmful than others, but in my experience no dust is ever pleasant to inhale (unless you enjoy sneezing and a hacking cough for some time after exposure).
There is also a potential hazard from the flammability/combustibility of many powders (both organic and metallic). In the past, some grain silos had a tendency to explode because the dust was appropriately distributed in the air and heated, and aluminum powder can react with heated metal oxide powders (grinding dust (http://web.archive.org/web/20071125064608/http://www.hanford.gov/rl/?page=542&parent=506)) in a violently exothermic reaction ("am I missing an eyebrow?" or worse (http://msa.hanford.gov/hills/Docs/OES_2007-07.pdf)).

Hex profile socket head fasteners are nice in general, but their nicest feature is that if the Allen wrench gets stripped then you don't need to buy a new one (just file 0.5mm or so off of the end until it is again a hexagonal profile). If the socket gets stripped, then the head is usually sufficiently long to grip with some needle nose pliers (stripped a couple when swapping the new FSR-equipped feet on a DARwIn-OP and pliers worked quite well in removing them).

Upgrayd
04-17-2012, 10:04 PM
Dave Jones Put out a great video of must haves if you are waning to put together an electronics lab. Obviously everything he mentions isn't required for robotic projects but It gives you an idea of what is used in hardware hacking.

Multiple good multimeters, bench power supply, solder station, and the range of hand tools he mentions are what I would require mandatory.


http://www.youtube.com/watch?v=R_PbjbRaO2E

EnderWiggins
04-17-2012, 11:51 PM
Oh right! A nice bench power supply would be amazing... I think I'll go pick one up too... hacked PC supplies and wall warts are annoying at best!

Th232
04-18-2012, 12:04 AM
I would just like to point out one bit here:


Multiple good multimeters

While this might be expensive, when you need more than one you really need it. Maybe get one now and the second some time later, but eventually you will need one.

On that note, since I haven't seen it mentioned, a good set of files, small and large. While a Dremel is good, sometimes you just can't beat a needle file to make a small cut or trim something.

lnxfergy
04-18-2012, 07:16 PM
1. Yup, the original Issydunnyet did use some lynx tubing for leg uprights. I highly recommend getting a frame kit for most of the bracket stuff, but the lynx tubing is a great addition to a regular frame kit, especially for those uprights. The parts won't line up in CAD, but will be close enough in the real world to work.

2. In addition to comments about not using long legs, I also would avoid mounting lynx tubes between servos (they work great for the servo->ground part of the leg, but not so well between servos as they start to work themselves apart real fast, for instance, I had a lot of trouble with this robot coming apart: http://forums.trossenrobotics.com/showthread.php?3639-The-Ultimate-Arbotix-Thread&p=35983#post35983)

4. All output is in C/C++ (note: avrgcc is not a full C++ compiler, you get classes, but no new/delete).

On tools, I highly recommend the Aoyue 937+ as a great $50 soldering station (you can get it off Amazon). I'd also recommend trying out a brass sponge as a nice $3 upgrade (http://www.sparkfun.com/products/8964).

-Fergs

Baranyk
04-19-2012, 10:08 AM
4. All output is in C/C++ (note: avrgcc is not a full C++ compiler, you get classes, but no new/delete).

But the compiler for the ArbotiX itself does support dynamic memory allocation? Or would I have to figure out someway to not utilize it for the code?

lnxfergy
04-19-2012, 06:14 PM
But the compiler for the ArbotiX itself does support dynamic memory allocation? Or would I have to figure out someway to not utilize it for the code?]

avr-gcc has malloc()/etc, but no new/delete. So, no dynamic classes without some interesting memory handling code.

-Fergs