Building Materials and Weighting

[Neuntoter]

Planning a 6 leg 2 arm+pincher bot. Think a crab or something like that.
I am trying to think up some cheap building materials. I have adequate wood working tools to use wood. Don't have plastic working nor pobably adequate tools for metal either one.

What about erector set, automotive repair items, or anything else?
Anyone have thoughts about decent building materials to keep costs low? Is there a cheap way to get into plastic forming or creation?
Just trying to get ideas and I don't have a huge budget.

The other portion of my post is dedicated to the weighting required to maintain stability while operating the front arms. I haven't seen this often and am imagining it is due to stability. Is there some kind of sensor useful to this end? I was thinking about using some form of moving weight  to help keep the center of balance.

[Gertlex]

Helter skelter addressing of a few things you brought up...

Cutting/drilling plastic is easier than wood, imo.  You can do a full design with flat plates of whatever material you choose (aka bending/forming isn't needed), but this can take some trial and error, and design probably ought to be done in CAD.  If you have a dremel, that'll work nicely for plastics.

Erector sets will probably work nicely for a variety of things.

Hexapods don't really need to worry about center of balance.

All the actuators for 6 legs plus arms probably isn't going to be cheap unless your bot is very low weight.

[Neuntoter]

Cutting/drilling plastic is easier than wood, imo.  You can do a full design with flat plates of whatever material you choose (aka bending/forming isn't needed), but this can take some trial and error, and design probably ought to be done in CAD.  If you have a dremel, that'll work nicely for plastics.

Hmm interesting on the plastic front, I figured you would have had to had special equipment for it, I would prefer plastic then. However where would one go to get a sheet of it? I am in the US, and sure there places but simple googleing did not find a place.
I have a base design in autocad, and a dremel. Just missing a place to cheaply purchase the materials and having trouble weighing all the options.

Erector sets will probably work nicely for a variety of things.

Hexapods don't really need to worry about center of balance.

All the actuators for 6 legs plus arms probably isn't going to be cheap unless your bot is very low weight.

I might go with Erector set as I could build and change things quickly and cheaply, found some sets that are cheap and seem rather generic. I am curious though how easy it is to mount the servos to them, am I going to find most servos have screw holes?

Well the easiness of balancing was one reason I went with the hexapod design, as I knew it would be decent at supporting it. So it would be nice if it was weighted enough not to lose balance on it's own.

The cost is a bit troubling yes, my bot will be pretty small(if it can work as planned) so hopefully I can find some decent servos cheaply. I haven't really done enough calculation to figure out bare minimum but I plan to get some that can be used in other projects so I am guessing most of my budget will go to them. Although I plan to purchase a couple at first to get things worked out.

[Gertlex]

Cutting/drilling plastic is easier than wood, imo.  You can do a full design with flat plates of whatever material you choose (aka bending/forming isn't needed), but this can take some trial and error, and design probably ought to be done in CAD.  If you have a dremel, that'll work nicely for plastics.

Hmm interesting on the plastic front, I figured you would have had to had special equipment for it, I would prefer plastic then. However where would one go to get a sheet of it? I am in the US, and sure there places but simple googleing did not find a place.
I have a base design in autocad, and a dremel. Just missing a place to cheaply purchase the materials and having trouble weighing all the options.

I've not bought much plastic, really... Much of what I've worked with has been Lego and scraps.  But you can get almost any raw material from places like McMaster-Carr (mcmaster.com).

The one tricky bit with working with plastics and power tools can be that the plastics like to melt a bit, and can require lots of prying plastic off drill bits.  (I don't mean the whole part will melt, just that rather than sawdust everywhere, you'll have plastic bits everywhere plus blobs of melted plastic that you can easily break off of your parts)

The one plastic I have bought is Delrin.  It has the advantage of being a teflon derivative or something, and thus a higher melting temperature, so less melting plastic when I dremel it.  Slight cost premium, though.  Most plastics I've used are ABS (3D printers and LEGO both use ABS), and this is one of those with the melting "problem".  The other common plastic is HDPE - possibly what most people use.

Erector sets will probably work nicely for a variety of things.

Hexapods don't really need to worry about center of balance.

All the actuators for 6 legs plus arms probably isn't going to be cheap unless your bot is very low weight.

I might go with Erector set as I could build and change things quickly and cheaply, found some sets that are cheap and seem rather generic. I am curious though how easy it is to mount the servos to them, am I going to find most servos have screw holes?

Well the easiness of balancing was one reason I went with the hexapod design, as I knew it would be decent at supporting it. So it would be nice if it was weighted enough not to lose balance on it's own.

The cost is a bit troubling yes, my bot will be pretty small(if it can work as planned) so hopefully I can find some decent servos cheaply. I haven't really done enough calculation to figure out bare minimum but I plan to get some that can be used in other projects so I am guessing most of my budget will go to them. Although I plan to purchase a couple at first to get things worked out.

I wouldn't necessarily buy the erector kits unless you're sure of how you're going to use them (I was inferring that you had them lying around already).  A similar, more robotics oriented product are the Vex Robotics kits.

Servos seem to fall into two categories, hobby servos (Hitec/futaba), and other servos.  The hobby servos are pretty standardized in sizing and mounting, but the mounting options are not wonderful, in my opinion.  Most people use these.

There are a variety of brands in the "other" category.  Currently I use Dynamixel servos (AX-12 being the cheapest kind), which have their own line of brackets and lots of mounting holes that make custom mounting easy.  They are however not nearly as cheap.  But if you ever find yourself considering buying metal gear hobby servos... go with Dynamixels instead.

I've done a poor job at staying cheap with my robotics hobby, in case you were wondering.   I would definitely recommend starting off with the $50 robot.  I did mine with Lego + Axon microcontroller, and cheap servos.