Candy Paint and the Hail Mary Finish: Last Update before Motorama

Friday, February 14th, 2014 @ 17:22 | Bots, Candy Paint & Gold Teeth, In Progress, Project Build Reports

Over the past few weeks, I was supposed to complete Candy Paint & Gold Teeth – especially taking this past week to do so. However, real life has a way of trying to happen all at once to me instead of in reasonably scheduled chunks. This often manifests itself in trivial instances such as a delivery guy showing up with a pallet jack at the same time I’m trying to answer a student question about machining, all the while my phone starts ringing. During all other times, I am a lazy bum.

This past week, it manifested itself in the entire shop being room-swapped, almost like out of some bad redecorating show:

Yes, that is the Shopbot, in all its 5 x 10 foot glory, mounted on a pallet jack and a trash can rolley base. With zip ties.

Oddly enough, I didn’t think this one up.

The former EE/laser cutter room was turned into the combination fab shop and Shopbot room…

..and the former shop had all of the EE equipment, rapid prototyping tools, and 3D printers stuffed into it!

Overall, it’s much more cozy instead of being a big patch of empty space. We did this to consolidate shop space in order to free up the massive area formerly occupied by the Shopbot for more researchers to have space. It was completely necessary, and (of course) this past weekend was the only window of opportunity: any later in the term and it would interfere with classes, and start of summer is too late because of the space needs of new researchers.

Besides that, the following also happened:

  • 2.00gokart Season 3 has started! This warrants its own post, but right after the shop was moved, I had to give orientations/machine training sessions to all of the 20 BRAND! NEW! excited students.
  • the Department of Facilities insisted that this week was exactly when they needed to wax the floors, so many of these things (but THANK ROBOT JESUS NOT THE SHOPBOT) had to be temporarily moved back out.
  • Mikuvan ate an alternator on Monday. This is reserved for another episode of Big Chuck’s Automove Blog, but this was a several-hours repair job yesterday after waiting for parts.
  • I had to teach a main-2.007 Solidworks lecture on short notice, which was a few hours of preparation.

What does this mean? Well, for one, I have almost nothing penciled in for next week right now, so I should just be able to sleep the whole time!

This post will recap Candy Paint’s progress up until last night. It’ll be short but pictureful. As it stands, there is a slim chance of the bot being completed right before check-in and inspections begin, so I’m just rolling triage – what can be done will be done.

First, the welded frame:

Hot. Damn.

I passed this welding job onto my friend Jack, who is the shopmaster of the D-LAB facility across the hallway. I wouldn’t have stood a chance – my only experiences with welding aluminum have always ended up in puddles.

This frame taught a lot of lessons – namely, I’m never going to do it again. I expected some “taco” deformation of the whole thing, but it was actually quite straight. What I found out later on was that many internal features had moved or warped out of place seemingly magically, and almost nothing fit the way it was supposed to. There was to be much Dremelling in my future.  I’m actually not sure why I wanted to go welded-frame in the first place… something about trying out new techniques. The frame was suboptimally designed to be welded – tight corners, very mismatched material thicknesses, and holes very close to edges, since my experience in design-for-welding is slight at best.

One of the first things I did was grind off some of those strength-giving fillets because the top of the bot needed to be flush – again, a design-for-not-welding guy trying to do design-for-welding. This will weaken all the joints, so I’m hoping the underside fillets and tab/slot mates make up for it.

A rough grit zirconia flap wheel made short work of the aluminum.

The finished result. I then took this downstairs to the giant 20 ton hydraulic press for some gentle frame straightening, using the bar that I messed up on the rolling machine as a flat jig. With this done, the next step was to post-process the holes:

One thing I am now aware of that is done is weld a blank frame first, then post-machine everything from a single datum. All of my features ended up moving around or warping – the big center hole’s bolt circle somehow shrunk almost .02″, necessitating Dremelling to remedy. I’m glad I invested in those carbide burrs.

With the frame ready – or almost, with an hour’s more Dremelling than I had intended – for drivetrain and other parts installation, it was time to make those other parts.

The center spindle is made from a single piece of 4340 steel. I single-point machined the giant 1″-14 threads.

I machined the giant center block from a 2 x 4″ brick of billet using the EZ-TRAK CNC mill in the auto shop. Here it is completed with one of the tapered roller bearings and spindle installed!

Waterjetting is easy, but billets are satisfying.

Stator and partially completed stator hub. The stator is a copier motor pull unit I had, the same size as the one in Kitmotter and one of the Razermotors. I’ll be rewinding this with only a few turns of ungodly huge wire.

It took a while to install the wheels, because all of the slots had shifted a little, warped a little, or shrunk a little. But this is what the bot looks like with all 4 wheels!

This is remarkably straight and level – there’s a tiny gap under one wheel. Oh well – after the first hit, I’m sure nothing will be straight ever again.

Installing the big center spindle block. This is a pretty integral portion of the bot, and it fastens onto all three major frame rails inside.

The little offset pocket is a zeroing error on the CNC.

Pretend-o-bot #1! The spindle isn’t constrained here, it’s just sitting in one bearing. This thing spins for a minute if I whip it up to speed…

I stripped all the windings off the motor and used a string to measure the length of new winding needed.

This motor will be spinning north of 15,000 RPM to drive the weapon bar at around 2500. To get this speed, I needed to make a very hot winding – I calculated that 4 turns, Delta-terminated, will be sufficient.

To make 4 turns and not waste all the copper space, I had to resort to very weird measures:

This is my “9x Hobbykinging Rig” from building the Chibikart motors. It places 9 strands of #28 magnet wire in parallel to simulate an easier-to-deal-with 18 gauge winding. “Hobbykinging” refers to the tactic employed on most Chinese r/c motors of using many parallel strands of fine wire to wind motors, as it’s easier on workers than trying to bend thick wire and fit it properly. Done right, it can achieve a higher copper fill than a single thick wire, but there is a diminishing returns point if the individual wires are too thin (such that the enamel insulation starts making up a sigificant portion of total cross sectional area)

To make the windings I needed, I calculated I had more than enough space for four runs of this. So, I wrapped the Hobbykinging rig 4 times around a 12 foot long table to yield 36 parallel strands of #28 – roughly equivalent to a 12 gauge winding.

This is what the winding looks like.

I actually enjoyed winding this motor immensely. It was so easy! Just sling the giant bundle into the teeth and pull. And only for 4 turns instead of 30-40 like the hub motors!

I wanna go work for Hobbyking!

The completed winding.

The  next step was to terminate the motor in Delta by bunching a start and adjacent end of another phase together (e.g. Start of A phase, end of B phase get bound together). I just ran the bundle out using heat shrink, then torched the ends to destroy the enamel coating, then used my Battery Abuser to tin the ends.

After this, I potted the bundles in epoxy to secure the windings.

Moving on to mechanical work again, it was time to assemble the drivetrain.

The sprockets were cut out a while back with the waterjet load. Here they are installed on the motors – and after some manual chamfer-filing while the motors were run under load.

A good amount of Dremelling and hammering was needed to move the mounting surfaces back to where they were supposed to be. The motors will hopefully be secure with their front and rear mounting brackets!

One side’s drive installed. Check out my little chain tensioner blocks – these are made from Delrin and are pushed into the chain with a set screw drilled into the frame.

Each side, after installation, got a 20 minute long run-in so the chain could carve its own path into some of the weld fillets. I came around and cranked the tensioner screw down little by little as time went on.

Now with both sides!

Most of the remaining work on this bot is just putting things in. I have to machine a (simple) shaft for the weapon motor, then it can be test spun. Electronics and batteries will most likely be installed ad-hoc.

I’ll leave the updates to Clocker to another post – so this will be the last one before Motorama. Now, back to the shop….

 

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