Category: RazEr rEVolution

Bigger RazEr for a Closer Shave

Pre-Everything Updates, August 18

chorl

I’ve been slowly knocking down the amount of half-taken-apart projects that have been taking up table space at MITERS. The usual shipping delays and distractions means I’m a little behind where I want to be,  but it’s not yet concerning. In other words, nothing has yet gone horribly wrong.

As of today,

  • Fix Überclocker!
  • Repair RazEr battery!
  • New motor controllers for LBS!

Pop Quiz 2

I received my shipment of carbon fiber from Dragonplate and proceeded to cut the top and bottom panels out on the same day. The CF this time is 0.023 instead of 1mm, so I lose some stiffness in the frame. I’m not quite sure why I chose the thinner panel actually – the scrapped PQ2 frame had 0.039″ CF top and bottom plates.

This was certainly one of the cleanest CF cuts I’ve made to date. I took several precautions this time to minimize delamination around holes and pierces, including fully double-sided-taping the carbon fiber to a solid wooden panel. Previously, I have either just clamped the CF to wood or taped the CF to a waterjet brick. The full support of the wood layer beneath the CF helped immensely – these cuts have almost no delam areas. The other methods would either allow the CF to flap up and down or still leave high percentages unsupported on the bottom.

The upside to this method is that I get a cute MDF billet Pop Quiz out of the process at the end. This was the backing for the carbon fiber after I stripped off the wet tape.

With Pop Quiz’s frame all printed and the CF panels cut, it’s mostly a matter of sitting down and assembling the thing. I got the VEX motor controllers in and also found my spare Spektrum BR6000 from who knows how many robots ago. Because PQ will be an experiment in using the VEX controllers, I’m going to rewind the weapon motor for 7.4v (2S) operation.

RazEr rEVolution

RazEr is officially all closed up and working again – the only thing the battery needed in the end was a charge and balance. God I love A123 DeWalt drill cells. What other kind of battery doesn’t mind getting zero-volted for a month straight? I don’t doubt that I have had some lifecycle and capacity loss because of the extended flattening, but RazEr is not a very high current system anyway.

This is what the battery looks like after I ripped off the layers of soda bottles insulating the pack. There are 2 balance leads, but no actual power connections associated with them – my balance-capable chargers can’t charge through the balance connector only. So this whole pack was kind of unserviceable from the start.

It also has bare balance wires passing directly over cells, something I recently learned was a very bad idea.

The resolution for this pack was pretty simple – add those power connections. The two Deans connectors represent the upper half and lower half of the cell. This enables it to be balance-changed by 4chan every once in a while to keep the cells level.

To insulate the balance cable better, I laid a layer of rubber cement underneath them. That will at least immobilize the wires and also keeps them, for the most part, out of potential electrical contact. Due to RazEr’s limited internal width, I couldn’t reroute the cables to the paper sides of the cell, which is what I would like to have done.

The final result, after coating with Real Giant Heatshrink!!! instead of more Mountain Dew bottles. Working with this was very refreshing – this is the massive thick rubbery PVC shrink often used for enormous power cable repair and the like. It actually doesn’t look like I threw it together in 5 minutes.

The Advanced Beast-it-troller

They’ve arrived.

From last update, the independent-input H-bridge version of the Beast-it-troller is now ready for assembly. Both of my Digikey orders for required parts, most crucially the IR2183 gate drivers, arrived the same day. Will it work?!

I also ordered (and received, too) a spare CIM motor to replace the toasted one in the left side drive. With luck, Land-Bear-Shark will be running (…again) for this upcoming Swapfest.

Pan-Project Update: Little things here and there

chorl1 Comment

Not much has happened in the last week or so with regards to anything reaching completion. Sadly enough, not even the melontank has escaped the wrath of final semester. I’ve been filling in some minor details on the vehicles, though, in part preparation for the Energy Night Showcase, which I’m attending with some cohorts mostly as an excuse to ride scooters around to annoy the staff, and partly because said scooters is actually a hardware display at the event.

razEr rEVolution

Ever since getting back from Singapore, RazEr has just been kind of hanging out around MITERS giving curious onlookers test rides. One day, however, it just stopped. I don’t recall if it was on acceleration or deceleration, but the entire controller simply shut off. Not in flames, to my utter surprise. Further investigation revealed that the ATMEGA328 chip that is the core of the controller just straight up died. I don’t know what the cause could have been to completely kill a microcontroller besides voltage transients above its maximum voltage – after all, the logic voltage is fed by the gate drive voltage, which is one step closer to the very noisy and high current battery rail. And I don’t use a hardcore switching voltage regulator like some other people do… rather, a completely rigged linear voltage regulator fed by a resistor.

So instead of, you know, fixing the thing to use a real voltage regulator, I decided to fix the symptom for now:

Dropped (almost literally) on the Arduino carrier board is a 5v transient voltage suppressing diode, and right next to it is a 100uF 1206 capacitor. Seriously – 100uF in 1206? What is wrong with the world?

The addition of massive buscap and a TVS should absorb any transients on the logic rail in the future. I’m saving the real parts for the full v2 redesign, for which I have additional upgrades in mind.

Another issue that Razer had faced before its untimely demise was some kind of strange, no doubt current induced behavior where the motor operation would become very unstable if full throttle (or really anything above mid-throttle) was applied. The symptom manifested itself as a sudden loss of torque, almost like the motor was spinning off a clutch somewhere and little torque was making it to the wheel. Now, I know I slammed that motor can together on a 20 ton arbor press, so there’s no way it could have been mechanical. Further investigations into the gate drive voltage revealed no significant “early shutoff” of the high side bootstrapped FETs, which could cause such behavior past a certain PWM duty cycle. I was out of ideas, so on a wild suggestion, I made a common-mode choke out of a nut and a few turns of 14 gauge wire.

It solved everything.

I’m not even going to ask. The Common Mode Nut will, for now, become a permanent feature on RazEr. It allows me to floor it with reckless abandon down the hallway (shortly before discovering the hard 90A urethane wheels, covered in floor dust, have zero traction in the waxed hallway corners).

landmelonbearsharktank

Not much news here, but I finished mounting the sprockets!

I made the spacers in the Pappalardo Laboratory, during my 2.007 lab assistant session. I decided to tow the entire thing to campus in order to do this, and the other students taking the class found it amusing that such a thing could possibly exist. Mission accomplished.

make-a-bot

Unrelated to the showcase, but still worth an update, is the death and revival of MaB. I had run out of PLA plastic (which sticks to everything) by printing like 8 versions of Chuckranoplan, and needed to revert back to my stock of ABS plastic. My surface heater had shed its thermistor a while back for whatever reason, meaning it couldn’t be software-controlled, and getting ABS to stick to cold plastic was a difficult affair. So I did what any reasonably intelligent person would do – hotwire the heater to 12 volts.

Backwards.

Luckily, I realized how backwards it was after a split second, so there was no cascading destruction of the entire electrical system, but it was long enough to bake the entire bank of ADC inputs on the extruder controller.

It took a while and alot of help from people with more patience for SMT soldering, but with the AWESOME MITERS HOT AIR REWORK STATION!!!! the ATMEGA168 on the extruder controller was replaced, and MaB was operational again.

While it was away, I got a reel of white ABS instead:

I like white ABS alot better. Everything doesn’t come off as a featureless black blob, and it changes color slightly dependent on temperature and how long it’s been cooking in the nozzle, so it’s one way to gauge if my temps are wrong within a wide band of errors (No, they’re not.) For some reason, it doesn’t smell as death-filled as black ABS. However, it does seem to lose a little more volume in the extrusion process for whatever reason.

That’s all for now. If anyone else is going to the Showcase, be mindful that I might broadside you at full speed on RazEr.

i’ll just leave this here.