Ãœberclocker Update 17: This is not funny Edition

Saturday, August 16th, 2008 @ 6:29 | Bots, Project Build Reports, Überclocker

Actually it is. From the past several builds, I have come to a conclusion that beginning exactly one week before I am to leave for an event, things will go horribly wrong that will leave whatever I am building crippled and disabled and unable to function up to its full potential. We saw this with TB4.5MCE for Battlebots IQ, where I lost an arm ESC and couldn’t obtain a main battery worth its weight in beans. TB4.5SP1 for Motorama had a whole third of the bot go out two days before I left, and only some last minute hacks allowed it to run at all.

There are plenty of rational explanations, of course, since I usually get to rigorously testing my engineered systems only in that last week or so, and untested systems like to break if they’re not properly designed and built. But the fun explanation is that the robot gods are just out to get me.

Oddly enough, nothing wrong wrong with NK except losing a LiPo cell, which is not a terminal disaster.

Over the past few days, I have been slowly wiring up Uberclocker. Working in an environment where everyone else is also working on something interesting means I get distracted far too easily, so it’s really taken _that long_ to wire the bot up.

Here’s most of the wiring. For a bot with 5 motors, 4 controllers, and 2 batteries, the wire layout is surprisngly clean. In this picture, the master power switch had not been mounted and no cell balancer wiring is installed.

This was the condition of the wiring for the bot’s first remote-controlled powerlift – the previous one was by touching wires to battery leads, which isn’t exactly a legit in-arena tactic. So what weighs more than or equal to a 30lber?

Well, at MITERS, plenty of things, but the only thing compact enough was this…

…45 pound rackmount uninterruptible power supply battery pack.

I approve of this bot. It can raise the 45 pounds pretty briskly and can suspend it in the air with no motor power applied (with the controller in Brake mode), and can bob it up and down. I don’t have an amperage number yet.

As expected, the back end of the bot lurched upwards on beginning the lift, but fell back down due to the support from the rollers in the front. I didn’t practice balancing the bot with a load on the rollers, but that should probably happen some time.

Then stuff broke.

First, while running the clamp arm with no load, the Banebots 12-45 controller popped its reverse direction. It was a very audible (and frightening) pop that made me think one of the FETs on the Victor 883 controlling the fork motors fried.This was strange, since I was using a motor far, far smaller than what the BB controller should be capable of handling, and it was not clamping down on something or hitting a travel limit. Just small reverse throttle.

So I have started the replacement-under-warranty process with Banebots. We’ll see how THAT one goes – chances are they’ll be considerate and ship me a new one in Atlanta.

After the mild scare, I decided to continue testing by dropping in the ANT150 controller from Nuclear Kitten. But again, that didn’t last long, because…

… the actuator motor shaft snapped. The B62 has a reported history of fracturing output shafts, and it looks like the bug hit me. However, it looks like the shaft actually broke in flexure, which tells me that the radial support at the base of the leadscrew is poor.

I’m not surprised. When the clamp arm hits something on its way down, the load on the actuator is essentially pure compression. Any buckling of the part connections at all could lead to catastrophic failure, which seems like what happend in this case.

This is bad. Very, very bad. Considering the whole leadscrew assembly was green Loctite’d together, it’s going to be nearly impossible to extract the broken shaft stub. A replacement motor is a hefty $30, and I’d have to buy and machine a new section of leadscrew.

Bad indeed. Without the upper clamp arm, Uberclocker is a giant spatula of questionable sexiness.

I’m now in the process of specing out parts and designing a new leadscrew machanism. This will be an indirect drive type device that will take the stress off the motor shaft itself. The motor, furthermore, will be mobile along with the upper clamp instead of being pivoted in a fixed location on the forks. Instead, the leadscrew will be fixed with a pin type joint at the base.

Using an indirect drive leadscrew mechanism, similar to the “beak” of my 2005 Science Olympiad robot, should make the whole thing more reliable anyway.

This will have to be fabbed in Atlanta, since I won’t get any parts I order now by Monday and actually get anything done. So with the clamp out of commission, I tied it to the fr0k to secure it and continued finishing and finalizing the wiring. I installed the battery balancer plug, another Convenient DB9 Connector of LiPo Balancingâ„¢ , physically mounted the power switch, and cut holes in the top plate to accomodate them.

Besides the DB9 connector, I also put in a direct connection to the battery using a Deans female side connector mounted to the left Ebay. For this bot, the charging current needed will exceed the limitations of the 24-22 gauge wire that fits in the DB9 connector, so I will use that only for the charger’s balancing function, and the big connector for actual charging current.

After tidying up the interior some, it was time for a beauty shot. Cheesy cell phone camera style.

The bot’s now only missing stickers and blinkenlichten.

And also the signal module. The signal module is my name for the receiver + fork controller combo that will occupy the left side Ebay. The fork controller will take input from the Spektrum Rx and do two things – one is buffer the signals for the Victors, and two is correlate my transmitter’s Throttle stick position with the position of the fork. It will take input from the potentiometer mounted to the fork and drive the ESC accordingly.

I decided to let it process al l the receiver signals (and passing drivetrain commands straight through) instead of making a separate buffer board for the drive only – it keeps the wiring cleaner and allows for future expansion of more advanced control schemes.

There is minimal hardware left to implement, since the microcontroller already comes with its neato support board.

There are exactly three days left. Can I get everything working?!?



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