Bone Dead Robotics

[Koolaid64]

in what bot?

[zacodonnell]

The center mount is looking better Brandon, but I still think you could make it stronger without adding much weight. Right now it looks like you screwed blocks of plastic to the base, then screwed down through the top block of plastic into those blocks.  It would be a lot stronger, and not rely on plastic threads holding as much, if you just passed bolts straight up from the bottom, through the blocks on the base, through the top part, and then put nuts on them.  This is basically how I did Tripolar and it held up very well.  Leaving the plastic a little space around where the bolts go through will help prevent pull out too.

A hardened shell would hold up better... but a warped shell might never spin.  Whyachi can do the hardening but it is an expensive process to fixture the part so it won't warp and use a hardening process that reduces warpage.  I've never been brave enough to actually do it and have stuck to an unhardened 4130 shell for all my 30 pound bots.  They do eventually warp, but with enough clearance they can maintain their shape for a while if you design them right.  The warpage over time is the reason I couldn't spin with Tetanus in the Motorama final last year.

-Zac

[BranYoung]

To Kyle: In that 12lb spy cam robot. The reason is that the overall size is huge on that robot and I don't have enough material to make the rear guard without making it two separate parts which weakens it. by shrinking it in, there is less wasted space and I have enough material to surround it.

To Zac: I may very well do that. While those screws shown in the picture do penetrate and hold, a through-bolt adds additional structure and rigidity. What exactly do you mean by "leaving the plastic a little space?" Do you mean a longer top guard that has more overhang which provides room for through-bolts or possibly to separate it a bit more from the collar and shaft?

[BranYoung]

Would Fingertech's 3mm HTD pulleys be suitable for use in a 12lb wedge's drive system? I know they are kind of small and not as beefy as other examples, I have some on hand and I am really interested in testing them out.

[FingerTech]

You should try it and let everyone know!

[Lucas Grell]

Would Fingertech's 3mm HTD pulleys be suitable for use in a 12lb wedge's drive system? I know they are kind of small and not as beefy as other examples, I have some on hand and I am really interested in testing them out.

We've used them with the really narrow belts in 15 pound bots. Only ever lost belts when stuff went very wrong with the side plates on the bot.
I kept telling the guys building it to make them stronger, but no, they're fine, they said, nothing will go wrong this time, they said.

[Lucas Grell]

That'll work fine. Are you going to leave the wheel mounts and the like that rough or are you just prototyping?

[zacodonnell]

To Zac: I may very well do that. While those screws shown in the picture do penetrate and hold, a through-bolt adds additional structure and rigidity. What exactly do you mean by "leaving the plastic a little space?" Do you mean a longer top guard that has more overhang which provides room for through-bolts or possibly to separate it a bit more from the collar and shaft?

I just meant make the top plate that the bolts go through a little wider than it needs to be so the bolts aren't right at the edge. It will reduce blowout from horizontal loading against the bolts and not cost much weight.

I'd bet the 3mm HTD belts would be fine for a 12 pound bot if you get the tension decent and don't make the pulleys too different in size.  You'll want to keep as many teeth engaged at a time as you can, at least 5 or 6.  I used 5mm HTD x 6mm wide belts on Tetanus and never showed any signs of wear.  The wheels were tiny though. 

-Zac

[BranYoung]

Some more progress



Put some paint on Terrorpin thanks to the nice weather. Now it has that "Evil Fish Tank" look



Attached some fingertech pulleys to the drive wheel.



And to the roller wheels



Possible configuration. The only catch is that I may not have all of that assembled enough to go to Motorama with it so I may put it in previous configuration just to have it in one piece.

Comments/concerns?

[zacodonnell]

That's a pretty short wheel base with seemingly pretty large wheels. Do you think the 4wd will make much difference in that configuration over 2wd? The offset motor and idler pulley strategy has worked well for many builders, but make sure you have enough time to really test it before bringing it because it can be tricky to get the belt tension right. You don't want troubles with that because you rushed through it.

-Zac

[Lucas Grell]

The main advantage, IMO, of 4wd is that your bot is much harder to get stuck with one wheel up in the air spinning while everyone else laughs at your 2-wheel bot.

[BranYoung]

To Zac: The fact is that I would need to buy some more metal base because the belts I have are set up for a 6in wheelbase (from the center of each wheel) which is more beneficial for control anyway. Besides, if I left it that short, there would be too little for the battery and that Sabertooth.

To Lucas: I agree, that ability to remain in contact with the ground more often is why I built Terroropin as a Trilobite-esque brick .

[zacodonnell]

Speaking of the Sabretooth... I just mailed it to Jason H with the Hortinator.  Of course you could always buy one if that is what fits.

-Zac

[BranYoung]

Final group photo. That overhead antweight is something I threw together without any proper inspiration for a better design. Unfortunately, I smoked a R410 Hobbyking receiver while trying to work on it so now I have no more backups and I have no way to even test out that little guy or CATAPULT. Anyone got spare receivers?

[Badnik96]

You could always take out the receiver from PK if you need to. Ant looks good.