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Thursday, July 10, 2008

From My Lens To Your Screen

Here are most of the promised pics of the updated Friction Drive 2.0, now at 2.0.2. Something wierd is going on with Blogger at the moment, as it won't let me upload anything else (it just sits there waiting forever after submitting), so I'll add more later to a new post if it starts working better later. I did get the motor test video to upload; it's at the end of the post.

These are the left and right views of 2.0.2, with not much visible change from 2.0.

In the left view (showing the left side of the bike), you can see some new heatsink fins at the rear (righthand in pic) edge of the motor panel. That's where the 2 MOSFETs, 2 driver BJTs, and 1 dual-diode pack are now mounted to. The heatsink is out of an old active-air-cooled car amp, used here mainly because it fit between the space available between the rear triangle legs and had enough spots already built into it's clamping bar to hold all the parts I needed to keep cool.

In the middle view, you can sort of see the controller itself, to the lower left of the top motor, but it's mostly behind the tire in that pic. What you *can* see here is the clamping bolts and plate added to the roller skate wheels on the motors, which now clamp those wheels firmly to the motor hub. Unfortunately, without a drill press, I was unable to keep all the holes perfectly lined up; this results in a small but noticeable wobble of each drive wheel, which is magnified many times at higher speeds of the rear wheel, causing the rear wheel itself to vibrate (in combination with it's imperfect centering during my wheel relacing & rebuild, which I need to redo).

In the right view is a closeup of the righthand side of the bike, looking thru the rear wheel into the space between the PWM controller and the heatsink. The controller itself is partly visible towards the upper middle of the pic. The two electrolytic caps partially visible behind the rim come quite close to that rim, within a few millimeters--they're unfortunately the shortest I could find in my salvage that have sufficient capacitance at a high enough voltage rating to deal with spikes, etc, and still physically fit in the space on the existing salvaged PCB. A single much larger and much shorter cap will also fit there, but it gets significantly warmer than two of them, due to the current flow inside it as it tries to stabilize the voltage across the motor during PWM cycles. There are caps made that will do what's needed and fit and be shorter for better clearance, but I'd have to purchase them new, and I'm trying for as much recycling as possible.

Some parts I already *had* to use new (but didn't have to buy), like the 100v / 123a MOSFETs, which can easily handle the power levels involved in this ebike version. I simply haven't found anything remotely powerful enough in the salvaged components I've collected so far, even if I were to parallel quite a number of them--I don't have enough of them with the same characteristics to make a difference, and mixing them could result in unpredictable behavior, as some might begin to conduct before others, or stop conducting later when turned off, derate differently across the power and temperature ranges, etc. Potentially could cause catastrophic failure, and that would probably be at the worst possible moment, when I most need that extra power suddenly. That's why I went with the new MOSFETs. The driver transistors are salvaged, though (they were the MOSFET drivers for that audio amp--the MOSFETs themselves were physically destroyed, but the drivers were miraculously fine).


Some closeups of the top motor drive wheel, 2.0.2 version.

Bottom drive wheel.

The bottom wheel is more precise, and wobbles much less--it was also the second one I did, so when I make some spare wheels for this version (as it works well enough to keep around as a secondary bike's drive system, even after I get a better system going on this bike), they'll probably be even better than this one, even with just hand tools and a power drill.

The hole in the center of the clamping plate on the wheels is to be able to install/remove the nut securing the wheelhub to the motor shaft, as that's most of the way inside the wheel (these motors have *very* short shafts).

The black stripe on the skate wheels actually appears to be some tar/asphalt picked up by the bike tire bit by bit and transferred to the rollers; they're sort of "gooey" when very warm, and pickup stuff like that the way Silly Putty picked up newsprint ink. :-) The tire itself does show some wear from friction, but mostly that seems to be from the deliberate loading tests I did, such as braking with motor power at full throttle (to make sure I *could* stop in the event of controller failure in that mode, and yes, I can, albeit about 4-5 feet longer stopping time).





Closeups of the new heatsink.

It's attached via 3 rackmount screws threaded directly into the aluminum plate of the motor panel (I just drilled holes 1 size smaller than the threads of the screws). Plain old white heatsink compound (from an old CPU heatsink kit I'd used Arctic Silver III on instead) fills airgaps and scratches between the motor panel and the heatsink, as well as between the components and the heatsink.

This assembly is placed in such a way that airflow from the spokes going past cools the MOSFETs, drivers, and diode pack significantly--about 17F cooler than if I put a plastic barrier sheet between the spokes and the controller/heatsink. Unfortunately sometimes I have to sit still for longish periods (3-5 minutes) at some intersections for either left or right turns, during high-traffic times. That keeps the already-built-up heat from having much of a place to go besides spreading thru the entire bolted-together aluminum assembly while I'm stopped, so I might add a temp-controlled small fan (have a bunch, need to test best characteristics

Some of the parts used to create the drive wheels:

The aluminum framework is the bottom of the camera stand, so you can just ignore it.
The two blue ones are unaltered skate wheels, to be converted as spares. The black one is the nylon-ish core of the skate wheel that disintegrated during 2.0's first test run. There are two of the bearing sets next to the black wheel; I don't currently have a plan for using those on this version, but I might need them for a jackshaft-wheel or idler on another thought I have pondered.



These are pics of the brakehandles I'm rebuilding to contain a pair of N.O. reed switches for braking. One will be used to switch the brakelights on, one will be used to switch the PWM controller off or into standby/braking mode. It would be simpler to use only one switch per brake handle, but right now the lighting and the motor systems are on two separate battery supplies, one at 12v and one at 36v. That's sufficiently different that any cross-connection of the system is going to destroy *something*, if done at the braking point, due to the way the PWM controller was designed.



And now the 45-seconds you've all been waiting for, the test video. Keep in mind that since the bike's baskets are being held up by two empty rubbermaid dog food containers, which in turn holds the rear wheel off the ground, there's no load on the rear wheel, so it accellerates faster and decelerates slower tthan miight be expected.
video
The wobbling of the wheel (which shakes the bike) is partly from my rebuild of those baskets, but really that shaking isn't that bad or noticeable when riding on the road.

Maybe more later--I'm literally dozing off at the keyboard....

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