View Full Version : Leg's too close?

11-02-2010, 01:46 PM
I came up with a possible bipedal design last night, and I wanted to double check some of the bots posted here to see if I had a reasonable layout for the controller/communications boards. After scrutinizing DB's "Hi No Hikari," UncleBob's "Knight Templar II" and Ty's "Giger" this morning, it winds up that the four hip & torso servos I've laid out are set very similarly to Giger's design. The main difference is that I have the torso's pan & tilt servo's stacked ontop of the two hip servos (with the hip servo's being aligned much as Giger's are). I have the vertical axis of the legs offset slightly towards the outside, but I'm wondering if the legs would be too close? I was trying to keep the hip width as narrow as possible and that's why I decided to put the panning servo stacked ontop of the hip servos, but placing it just like Giger's - between the two - would certainly help lower the CoG.


http://img269.imageshack.us/img269/3152/11compbi0302.th.jpg (http://img269.imageshack.us/i/11compbi0302.jpg/)

11-02-2010, 03:09 PM
This design seems very limited in mobility, as I don't see any hip tilt servos. (The ones that allow you to do splits.)

11-02-2010, 05:15 PM
True, but that's the way I had meant to go with mannyr7. In order to help keep bot costs down (as I'm basically starting from scratch and getting the basic fabrication equipment now to start off with as well), I want to keep the number of servos to a bare minimum, since I will be going with RX-24Fs instead of the AX-12+s (this is also the same reason why I switched off from the quad as I know that I'll be going with heavier mechs next year and I don't want to put my resources into servos that aren't going to be carried over and reused for at least two years running). This is strictly a "shuffle to points A-B-C & shoot" Mech-Warfare bot, the only activity I'm entering for RG'11. I had been thinking that I wouldn't need to concern myself with humanoid/kung-fu competitions, where I'd have to have the bot be able to right itself. Having said that, you did bring up a rules oversight on my part, as I had presumed that one would be able to manually upright their bot for MW - I'll have to post that question in the rules thread and see. If that's frowned upon, or straight up against the rules, I will have to re-configure the legs accordingly.

Thanks very much for the reply mannyr7, very much appreciated. :)

Here's a revised JPG of what I'm thinking of (it's not to scale, obviously missing brackets and such - just realized it's also missing a location for the battery! :/ - and I have to find out about possible mounting configurations for the Arbotix and XBee):

http://img530.imageshack.us/img530/6315/mwbasicbot002a.th.png (http://img530.imageshack.us/i/mwbasicbot002a.png/)

Even if the legs are too close together with the way I have it laid out (and with all else being equal), I may still go with the "stacked" pan & tilt servos and just space out the two servos I have for the hips, since having the additional difference in elevation gives a wider tilt range to the guns.


Here's a corrected JPG, showing the panning servo in the profile view (purple-colored ankle servos):
http://img525.imageshack.us/img525/7030/mwbasicbot00203.th.jpg (http://img525.imageshack.us/i/mwbasicbot00203.jpg/)

11-02-2010, 06:33 PM
I hope i don't sound like jerk, its not my intent. I would loose the hip twist servos and have splits servos instead...Just my take. Also I've heard things about the RX-24s having heat issues when under load. your ankles are going to be doing a lot of work trying to tilt the whole bot around...Just something to think about.

You have also mentioned money being an issue, and trying to reuse materials from year to year without having any waste. Something to consider is this, you can't really compete with half a robot. From the looks of it your going to have 10 RX-24Fs? Why not go with a 2DOF per leg quad for year one? it would be a whole lot more stable for year one, and seams like a better use of the same number of servos.

As for the bots falling down I'll have to look at the rules again, but last year we had "sock monkeys" that picked the robots up for you when they fall down. One hitpoint penalty.

And as for the legs question, Hikari's feet step on each other if I'm not careful. Having the ability to widen the stance is crucial.

11-02-2010, 10:09 PM
Nothing wrong with your reply at all DB, thank you very much for taking the time!

I've learned that servos are susceptible to heat issues, but I didn't know that the 24s might need additional attention to heat management details. With that though, I'd thought that having a reduced number of servos and essentially no "arms" (the corrected JPG above has the two hoppers and guns roughly positioned as they would connect through brackets directly to the tilting servo), would help lighten the overall loads.

Point well taken about not being able to compete with one-half of a bot - although I'd interpreted my design as being "compact" rather than conceptually insufficient! :} lol, It seems one of the "perks" of inexperience is having perpetually rose-colored glasses. ;)

I hate to admit it but I hadn't thought about switching to a 2DoF for a quad - I've been pretty focused on the 4DoF I boiled my design down to, although I had "momentarily" :} considered a 3DoF (nothing wrong with a 3'er either, of course, just not what I had wanted to do). In making an earlier response to Ty, about budgets, I hadn't considered the "major" expenses for some shop equipment - a good $600 to $800 worth of equipment. So, for me, that comes out of this years "bot budget."

I was all set to jump in and start buying components this week, but I think I'm going to take the week to sharpen my pencil and see just where I can tweak the budget and set some priorities.

As for the falling down Fergs definitively answered that but thanks as well on that point, and I'll also consider what you've mentioned about Hikari's feet.

Again, thanks DB, very much appreciated. :)


11-02-2010, 10:35 PM
What shop equipment are you planning to get. I get by on a $100 band saw, and $150 drill press. I think I spent $20 on my vice, and maybe $10 on my hammer. Maybe...Probably less. Oh, and a cheap set of precision screw drivers, lines man pliers, sheet metal pliers and a soldering iron. (radio shack...maybe $30 total.) You seam to be trying to buy for the long haul. Which isn't a bad idea, but consider I've had my band saw with no problems outside of a changed blade in 4 years, and my drill press for the 6 years I've been married. I've managed to make my last 6 walkers using almost nothing more.

As for a 2 DOF quad vs a biped, trust me you will have more fun with a quad. Your biped will end up slow, barely qualifying, and then completely out maneuvered and destroyed by AX-12 based quads.

I really hope this helps.


11-02-2010, 10:47 PM
I was looking at some Craftsman tools - a table top bandsaw and table top drill press as well as a table saw. With those I'd make a thermoforming unit, and I was also considering the 'desktop cnc' I'd seen advertised numerous times in Robot magazine, but I may look into hacking a couple of old HP ScanJet II's to go the home built route on that - but with my plate as full as it already is I don't see that happening. If I get the CNC set up then I also I want to setup a small home foundry for casting aluminum. Can't do it all this year but, that's the major bits and pieces on the list for now.


[PS: And yes, I am looking at the long hall; I want to be involved with robotics for the rest of my life, be it 2.5 seconds or more...hopefully much more, God willing! :D]