RX-28 PLM Humanoid

[Tyberius]

Hey guys,

Next month I'll be traveling to S. Korea again to compete in the International Robot Competition 2010 at the Robot World Convention in Seoul. One of the things that was asked of my team was that I compete in both the lightweight ( < 2kg) and the heavyweight (> 2kg) competitions. Giger Fu is the obvious answer for the heavyweight, but I didn't want to show up with just a Bioloid Premium for my lightweight entry so I set out to design and build a new lightweight humanoid using the RX-28 and an ArbotiX platform.

My initial design was very similar to what I plan on doing for Giger's next revision, using 4 pitch servos per leg. The problem was that I could not for the life of me get it under 2kg. It ended up landing around 2.2kg regardless of what I did. Here's the first design for reference:



I needed to get it to about 1.9kg before I pulled the trigger on making this, giving me a bit of wiggle room for additional hardware, etc. My 2nd revision was a bit more barebones, removing 2 of the pitch servos per leg:



And here are a few renders of the bot itself:








Should have the parts finished by next week! I'll be sure to post build photos and whatnot.

[elaughlin]

Yes, it's here. Definately can't wait to see this thing in action.

[Psykoman]

Really cool robot. I like the design.

[Gort]

Looks like I need to step up my game. Boomer MK III gets the first KungFu match with the new humaniod.




http://mike-ibioloid.blogspot.com/

[Tyberius]

I'm actually struggling with juggling cost of the linkage system vs weight of the original design. The issue is, using the current idler hub assemblies I have on this prototype... I'd end up with roughly $600+ cost in hub assembly hardware for the linkage system. That's more expensive than the 4 RX-24Fs that I dropped for weight. There are cheaper ways than what I have implemented, but I literally have 4 weeks until the competition so I need to pull the trigger on a design by tomorrow at the latest.

Since I'm thinking this one through on Inventor, I'll share my alternative designs as I go, which strips some torso weight off of the original design and gets me about 40g from my target weight under 2kg.

[Slugman]

Can you drop a little battery weight instead? Don't know how much wriggle room you might have in power consumption with the reduced number of servos vs higher torque required from each, etc etc. Could you use a smaller battery capacity, & charge between matches?

[darkback2]

Just tie some balloons to the top.

[Tyberius]

Can you drop a little battery weight instead? Don't know how much wriggle room you might have in power consumption with the reduced number of servos vs higher torque required from each, etc etc. Could you use a smaller battery capacity, & charge between matches?

I'm already using a military spec 11.1v 2000mAh pack that weighs 122g, that's about as light as money can buy. Anything less than 2000mAh isn't going to cut it for the 10-15 minutes of runtime needed.

I'm down to 2040g right now, I have an estimate of 97.2g for cables so I'm probably going to go all custom cabling with a thinner gauge and cut exactly to length, that should hopefully cut 1/3 of the weight off of it.

[elaughlin]

Damn, this is getting down to the nitty gritty of shaving weight.

Anything you could do of size reduction of those arms? I think you are trying to keep the length to get good reach in the kung-fu, but maybe in the bulk of the arms, you could cut out some of the material in the middle, or thin them out?

Were you planning on using all aluminum again for the construction, or are you doing plastic?

On the legs, could you take out some of those horizontal struts?

[Tyberius]

Yeah, it's real close. Keep in mind the majority of the bots competing in this are Bioloid type bots using 16-18 AX-12s... to get in this weight class with 19 RX-24F's is going to take some serious design balance.

The arms don't weigh much at all, even cutting them in half only saves me like 20g. They're the only ABS part on the bot, I'm bringing like 6 spare sets to go through if I break them. The feet are kind of heavy, but I dont think I can replace them with ABS versions because that would flex too much. I've punched even more extreme cutouts into the legs, and saved a whopping 9g. I really think that cutting down cables and using like 6 bolts maximum for each servo horn/idler is going to save me some. My last resort is removing the torso pan servo if I get everything here and can't get it under weight.