Make-a-RazEr Round II

Monday, January 10th, 2011 @ 15:36 | Make-a-Bot, Project Build Reports, RazEr rEVolution

Remember the trippy PCB?

During the last few days, I finally got around to installing it on MaB. I must say that the hot build platform made a tangible difference for large surface area parts. However, I also found out that I need to study PCB heater trace design more, since it turns out I designed the trace length without remember that resistance increases with temperature. That means this trace actually reaches thermal equilibrium when the temperature is about 95 C. It literally can’t get any hotter on 12 volts. I’d need to rig 15 volts or 18 volts to the thing somehow if I wanted the temperature to reach the 110 to 120 degree temperature that ABS is usually deposited on.

Oops. But, even 90 degrees has enabled me to start printing large structural parts. We’ll get to that later. First, the trippy PCB.

The aluminum plate will be bonded to the PCB with some kickass silver-filled epoxy. I imagine it’s kind of like Arctic Silver heatsink paste with a dose of resin and hardener in it. This little bubble cost $23…. so maybe next time I will just mix Arctic Silver with a bit of epoxy and call it a day.

For reference, the McMaster P/N is 7661A11.

The mounting process is just like applying said heatsink paste to your expensive multi-core unlocked CPU. I was surprised the stuff could be spread so thin, but I guess thin is better for heat conductivity.

The hole in the middle is to jam a little thermistor in for temperature readings.

The piece of Uniform Thermal Mass goes on…

…and is held to set with about 80 pounds of steel. This picture was also taken before I applied ~18 volts to the thing and let it bake under pressure while setting.

Next, I attached the thermistor to the underside. I later came back and edited this mounting with more Kapton tape and a little fuzzy ceramic blanket (the same stuff that is wrapped around MaB’s extruder, and comes in the kit).

And on it goes.

I ran a few bonding experiments with ABS to see what kinds of build surfaces performed the best. First off, bare aluminum is just not happening. Nothing stuck, at all.

I used the 6 inch wide Giant Kapton once, but also got very poor sticking performance. I’m led to believe that the temperature deficiency is to blame, since the greater 3d printing community reports good performance with ABS at 120 C.

Overlaying a piece of acrylic (i.e. the original Interim Build Surface) and letting it heat up worked great, but what the hell is the point if I have to keep laser cutting and replacing the acrylic slab?

Finally, I went and bought some blue painter’s tape, which is the other favorite of the Internet.

BUNNY… well, half a bunny.

Go figure, it works great. This kind of tape is also known to work when cold, which could come in handy for small parts.

I found that the tape’s adhesive was less than full strength 90 C, which caused some parts to lift if they were placed right next to a seam. The solution was to drop a perpendicular layer of tape over the strips to anchor them down better. That, or make sure the part is bigger than the seam.

With the heated build plate, I was able to embark on some large surface-area prints that would have failed before due to warping or the next layer not being able to stick.

I made this cute mecanum wheel as a test of a LSA part. I’m not currently working on anything that has a mecanum wheel, but it was a good test of 45-degree overhung holes too.

Finally, I went all-out and decided to make a part so large it literally takes up my entire build surface. As in, the Z axis was about 1/16″ away from colliding with the table as it passed by on the furthest lines.

Something remotely this huge wouldn’t have made it past the base layer stage on the old acrylic platform for sure. I also noted better perimeter adhesion than previous unheated prints, though I would also wager that was due to me setting the “first layer head height” lower, telling the machine to mash the first layer down harder.

So what can it be?

Okay, so it didn’t quite work.

But it’s a Pop Quiz frame. I selected PQ as a good candidate to try and 3d print the entire frame at once for, since it’s small, flat, and exhibits no strange shapes or overhanging layers.

It started out well, but it seems even large surface area parts have a limit as to how large they can be  on my current setup. The corners are all lifted about 1/8″ or so, which means the frame is pretty much unusable. I suspect at a certain point, just the surrounding ambient air is enough to upset the thermal equilibrium of the part – especially when there are alot of people walking by or working near, causing breezes.That’s why commercial 3d printers have their entire cabinets closed and heated to 90-100 C.

I don’t think I can pull that off yet, but when the second iteration rolls around, it might be worth a shot.

razEr rEVolution

Make-A-Bot has proven itself  now as my first maniacal creation which can make parts for my other maniacal creations. I see a thousand ways this can end badly, but in the mean time, Make-A-Bot is now fully able to print structural mechanical parts. The first real task I assigned it is to help finish RazEr rEVolution.

You know, the next open bracket that I paused for no reason in the middle of the term.  When I last left this thing, it had a motor with 33% functional Hall sensors, no controller, and a front wheel that looked like it belonged on a… well… push scooter.

Those first two problems are electrical, and so I will never solve them. But the last is mechanical. Let’s see what I can do about it.

This is a meaty, manly caster wheel from Surplus Center. I bought it with a shipment of melonshark parts as an investigation, and overall I like it. Most importantly,, it’s the same color as RazEr’s back wheel.

It came with the standard 3/4″ Enormous Roller Bearing center hub, which, needless to say, I couldn’t easily use. Those bearings don’t even start turning until you have a thousand pounds on the thing (but when you do, you’ll be really glad you have them). No ball bearings I had on hand were large enough to not fit into the center bore after the removal of the roller bearing. In other words, I was intending to just bore the center out, but didn’t have bearings big enough. A 6201 type bearing would have been optimal, but I only had 6001 bearings.

The first chance that Make-A-Bot got to be useful was making a bore adaptor for the bearings. This was a simple thin-wall tubular part.

I found out that the diameter difference between the bearing and wheel bore was too small for the software to route more than 2 perimeter layers. There was also a discontinuity in diameters between the bearing pocket and the center portion of the tube. Overall, I tried fixing it for 2 hours before giving up and just carving one out of Delrin on the lathe. Imagine that. Me, machining something again. It was a theraputic experience.

With the wheel bearing problem resolved, it was time to figure out how to mount this new monster truck tire. The stock Razor scooter fork that I had on the front is thinner than the webbing in the plastic hub of this wheel.

Instead of doing it Shane Style, I elected to see what Make-a-Bot could do.

The answer: Massive brick of ABS that happens to share the same mounting dimensions as the stock steel fork. This piece is a good 4 inches tall and 2 inches deep (in the above coordinate system).

Here it is imported into Skeinforge. It took a while to route just because it was massive.

I set the interior fill ratio at 50, so it ought to come out sort of hol…. wait, 50? Yeah, that’s actually 5000% fill. So it means I should be able to enter the 4th dimension and pull 49 additional copies out of this thing, right?

Anyways, by the time I figured out why it was doing every layer at 100% solid, it was already far enough along that aborting would have been foolish. I left, and returned several hours later to…


It’s replicating! AAAHHHHHH

…a hornet’s nest or something growing on my 99% done part.

A fellow MITERer told me that it seems to have just crashed at 99% and kept the extruder going full throttle for several minutes before it was discovered and shut down. Wow. Well, at least I can mill it off. The SD card I had been using was exhibiting file system errors, so that might have been the cause.

Unfortunately, after milling the tumor off, I discovered that some of the major dimensions were off. It didn’t actually fit on the fork since I made the two slits to fit the stock one too narrow. Even worse, the wheel rubbed against the underside of the thing.

Lame. That was like $5 of ABS right there. I should figure out how to recycle MaB’s own printer droppings.

So what’s next? Nothing except apply the changes and try again. Taller fork, wider slotting, and making damn sure it’s on 50% fill instead of 50 * 100% fill.

Here’s the result.

I must say, from afar, it looks very professional and almost like some kind of bizarre aftermarket upgrade for a push scooter. I would still need to make the 12mm wheel axle and figure out some kind of pin or bolt solution for the interface between the fork and the steering neck. The rubber block sits in the same place it did before and provides a minute amount of suspension-like behavior.

So is this part structural? It should be. I guess real testing will tell me for certain.

With the aforementioned pins and axles installed, the whole thing looks badass. The black ABS matches well with the black deck and contrasts nicely with the silver metallic aluminum frame. I should take up interior design.

Said pins and axles were popped out on the lathe after I spent about an hour trying to figure out how to print a bolt. There are some times where I should just learn to suck it up and beast it.

Also pictured is the piece I was making on Make-A-Bot as a test. It’s actually the front “window” for the frame. I might remake this piece from PLA plastic so it’s reasonably translucent, or embed LEDs into it.

A closeup of the front end.

I’m absolutely determined to bring this thing to Singapore in a few days. All that’s left now are fixing the DNIR motor’s sensors and making sure some variant of the Turnigy controller or Melontroller works by Wednesday. Then I need to figure out how to not evacuate both Boston Logan and London Heathrow with a scooter, two robots, and a set of electric ninja skates. I’ve never had issue flying with equipment before, but the sheer volume of it this time, combined with the international trip, might make things a little more interesting.

 

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    2 Responses to “Make-a-RazEr Round II”

    1. Dane Says:

      Some pics of the pop-quiz frame build are in the miters pool now. more to come.

      http://www.flickr.com/groups/miters

    2. Mike L Says:

      Hope you get all of the bugs with make-a-bot fixed also, i was looking at some older LOLriokart pics, especially kartoller 6, and where did you get those GE capacitors. I looked at two pics of different angles and the part codes, and found nothing, nor can i find any other large, medium voltage capacitors. Any idea of where to get them?