Monday, January 30, 2012

Razor Wind: I Hate Rain Edition (Upgrades!)

It is a well known fact that Saftey Razor may have been better than Razor Wind for one particular reason. Safety Razor's electronics were bundled and epoxy potted on the end of the motor, making for a very weatherproof and indestructible setup. While Razor Wind had better performance characteristics, it did not have nearly the same luck.

Last week Monday, we had some rather harsh thunderstorms roll over campus and I decided to ride the scooter in the wet. Story short, I noticed a little puff of smoke that was formerly the servo tester. I almost wished it was the esc, because unlike the servo tester, I have multiples of the HK escs.

Downtime means upgrade time, so let us look down the list of things I've wanted to do but never felt like opening a working device to implement.
  • Weatherproofing
  • New Throttle
  • Controlled Response from Throttle
  • Fanless esc (no random protrusion from the top)
  • Make it look pretty
Over the week, I've had the chance to tackle ALL OF THEM.

First, the esc needed a low profile modification in order to seal the upper deck. Simply removing the fan would have done the trick but without convective cooling I was worried about esc overtemp. So I went one step further and increased the size of my heatsink... THE ENTIRE CHASSIS.

Here we see the heatsink off the boards cooling WTF?! Traces?!

Even though the SO-8 package MOSFETs are designed to cool through the PCB, I wasn't convinced it was the best way to dissipate heat. The other side of the board had the ass-ton of FETs required to run, *shudder*, 150A.

So the obvious solution in my mind (at the time) was to resolder the components such that the FETs were exposed. So here we go desoldering all the headers and caps.

After an hour of desoldering, time to resolder.

It looked pretty shnazzy after completion. Some thermal compound would be added between the FETs and the aluminum heat spreader shown below.

The Aluminum of course would then be mounted against the base plate and the entire thing would be clamped down with some extra 2-56 cap screws. It is awesomely tiny compared to the stock product!

Testing indicated that everything worked as planned, but horror struck with I added the SILICON thermal paste to the FETs. I powered it up and I instantly lost three FETs on the startup tones.

The faults indicate that there was a short, which perplexes me because I had it running the night before. The only thing different between the two setups was the addition of NON-CONDUCTIVE thermal paste. Needless to say I'll be doing this differently next time. (un)Fortunately, Digikey has the NTMFS4833N power MOSFET for min purchase of 5000. Anybody else want to split a pack?

Speaking of indicators, Turnigy engineers impress me with the concept of a 'solder fuse', which tripped internally in my 6s 5000mAh lipoly pack when the esc blew. Probably saved me another 70 dollars right there.

This result was frustrating but not deterring. Using my last remaining spare, I decided to go forward with a variation of the mod. This time, we should use the heat transfer traces. This was nice because I only had the invert the capacitors.

Instead of solder paste, I pulled one of the heat transfer pads off the undersides of the heatsinks and tossed it between the aluminum heat spreader and the traces. This version is working flawlessly.

OKAY, so mod #1 completed. Now we can hit up weatherproofing efforts.

I figured most of the moisture was entering though the ventilation zone on the rear end but it couldnt hurt to seal up all the cracks. While performing the esc mod, I grabbed some RTV Silicon gasket maker and filled in the corners like caulking.

The opening over the esc was covered using a panel of 1/32" 7075 Al. I took the opportunity to make a water right exit for the esc plugs, which not only looks cool but also stabilizes the connection.

Note the blue edge around the top cover. The RTV Silicon seeped from the edges there a bit.

Fangoriously bright LEDs to indicate power through the scooter.

I hope I never have to test the functionality of my sealing job... Item #2 complete.

From my experiences letting other people try riding my scooter, it was clear that control was not its strong point. I attribute this to the rather shoddy rapid prototyped throttle I made last semester and the servo tester used to convert A to D.

So the throttle crazy began. I purchased maybe three different types of throttles (with spares. Say, does anyone need a throttle?) to select one thumb throttle from an ebay vendor selling 'American Chariots'.

Should you decide to purchase one, I'll save you the setup finagling and tell you the RED wire is +5V, the GREEN wire is output, and the YELLOW wire is ground. Not intuitive at all and I suppose I should be fortunate I didnt destory the thing.

I paired this new throttle up with an Arduino Nano (knockoff) to replace the servo tester. Not only was this guy smaller, but with some slick coding from Shane Colton I was granted control variables to handle throttle limiting and ramping rates. Exciting!

You can follow that right? Shane's Code can be found at the bottom of this Instructables page.

Items 3 and 4 completed! Finally, nothing makes things look awesomer than a bunch of reflective stickers.

Arduino Pride!

Sunday, January 29, 2012

Alternative Solutions for Things That Don't Fit

For people who find incompatibilities between some new object and the space the old one sat, there are really three options:

  1. Get a new environment
  2. Don't use the new object
  3. Rebuild ALL THE THINGS
I have a SFF case for my Lenovo M90 Desktop and wanted to increase my gaming/rendering performance by purchasing an new GPU. I settled on this nice Asus board, which had a ATI HD mobility Radeon 6570 attached to it, but when it came I quickly realized that it didn't fit in my case.

The top board is the new one and the bottom board is a NVIDIA GeForce 310. There was at least some .25" to .375" height difference due to the heatsink and as a result it touched the hard disk mounting bracket.

Yeah that's not much space...

Everyone seemed to suggest to buy a new case (choice #1). Myself, being a maker and machinist at heart, decided on choice #3.

Tada! It was easier to move the hard drive than move the PCI-E slot, so I redesigned the mounting case and shifted its location a fractional amount away from the graphics unit. Because we have 3D printers in the studio, I decided it was time to massively abuse them.

6 hours later...

Made off the Invention Studio's uPrint.

Old and the New

Part of the adaptation included slicing the wings off this cast aluminum piece. At this point, im pretty sure the warranty is void. 

The new mount uses 6-32 screws to attach to the hard drive, and some small perforations to clip onto the inside of the case. 

To keep things from bouncing around, I threw in stacks of leftover rubber grommets I bought for the Hardboard Project. Glad I could find a use for them.

So there it sits complete! Now I know what many of you are thinking. You are using melted plastic to hold a part nearby a notoriously hot object. Won't it melt? The answer is hopefully not. ABS melts at somewhere around 225 deg F, which converts to 107.2 deg C. The heatsink is not actually touching the ABS, and the convection currents internal to the PC should work in my favor, decreasing the edge temperature of the heatsink alloy and cooling the ABS. Besides, should my GPU get over 100 deg C I think I have larger problems to worry about.

And oh hey! 3D printed Soap!

Monday, January 23, 2012

Wheelpod: Chain Conversion

I found out about two weeks after I placed my order that McMaster's custom chain length item is meant for link numbers divisible by two. Awww shucks, I couldnt trick the system. I calculated previously a length of 51 links for a perfect chain length so they called me up one morning and handed me the unfortunate news. I would have been bummed, except I had already gotten tired of waiting and decided to beat it anyway with some surplus chain given to me by Aaron Fan.

The sprocket was the tricky part. Because I'm cheap, I neglected to buy any appropriately thick metal to cut #25 sprockets out on the waterjet. So I ended up with a 3/16" thick plate of mystery steel from the scrap pile. Most sprockets of #25 are some 3/32" thick with an edge taper. This piece of metal would require a good amount of working with some care for symmetry. My first thoughts were to add the bevels on the lathe, but we didnt have tooling shallow enough not did I want to disrupt the squareness of the toolpost. This is what I ended up doing.

Ah yes, I feel like a high school student again. That is a right-angle drill chucking a cap screw, which is holding a plate of aluminum that has the sprocket bolted to it. The assembly spins against a belt sander and adds a bevel (slowly).

Another shot.

Surprisingly enough, the technique worked well. 

Now excuse me as I tempt fate with my 30mph nonsense on wheels.