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Sunday, June 8, 2008

Twisting The Lime...Er...Throttle

First, I had to change out the old computer reset switches I'd used for the motor-disengage-when-braking switches on the brake lever--they simply weren't meant to be handled the way they were when my gloves rubbed against them and pushed on them, and started to come apart. It's ok, since they were only a temporary measure until I find my reed switches to replace them with.

However, since I still hadn't found those (until today), I replaced them a couple days ago with the ones pictured above--those used to be internally-lighted aircraft pushbutton switches, from some cockpit control panel (I don't know what it was, there wasnt' much of it left when I got it in a junkbox from someone else, maybe 20 years ago or more). The lights aren't connected, just the momentary normally-open switches. There are still two of them because I want to be sure my gloved hand pushes at least one when I grab the brake in any sudden stop situation. It would suck to be unable to stop as fast as needed because of the motor still running during braking. :-)

When I get to reworking stuff for 2.0 of this friction-drive setup, I'll replace them with the magnetically-operated reed switches, which will require no thought or anything--they'll automatically just work when I pull the brake handle even a little bit (as the brake light does now). Note that the reason I don't just use the brakelight switch to do this is that the motor controller is on 24v/36v, and the lighting is on 12v--it would be more complicated for me to cross the two systems at this switch than to just add a second switch.

Now for the throttle update:
The slider throttle really wasn't very good, nor safe/easy to use, so I built a temporary twist throttle out of what was left of the plastic Scoot'N'Go throttle body (since it came apart shortly after I got the scooter's corpse). It had been a Hall throttle, but the plastic was broken in such a way as to be unable to really restore that function in any reasonably easy way, so I converted it into a rotating-potentiometer throttle.

I took the grip off the handlebar on the right side, added some strips of plastic (cut from the inner liner of a dead scanner I recently picked up from Freecycle to use as another headlight for a different EV idea) on the inside of the end of the handlebar, so the potentiometer (pot) would fit snugly into it and not rotate with the throttle, but not have to be glued or otherwise secured in, as I intend to change it to another design later, once I've had time to perfect the other idea.

The pot itself is from an old wonky VGA monitor that was donated to me a while back, I think from the horizontal hold. The plastic knob for the pot happens to be just a bit shy of being the same outside diameter as the throttle body's inside diameter, with one layer of plastic on the inside of the throttle body making up the difference, with just a bit of light sanding on the outside of the knob to make a snug fit. The shaft of the pot sticks out of the handlebar just a little, which meshes up with the knob's length so that the knob is almost entirely within the throttle body when it's all mounted on the handlebars.

The throttle body also doesn't fit the handlebar perfectly, as it was meant to be held on with a couple of set screws from the bottom on the mounting ring end, but that is the end that basically doesn't exist anymore (it's in several dozen pieces, where it cracked apart). So I shimmed that with plastic strips, too, with the wires to the pot running in part of the gap between the throttle body and the handlebar. I might drill a small hole in the handlebar just between the shifter grip and the throttle grip, and run the wires *inside* the handlebar, but that depends on how the other design (using a Hall) works out, since that version won't have any moving parts. Since it works as it is, well, I'll probably just leave it the way it is. If it breaks, I'll modify it.

The wires at the pot end are secured to it with silicone to provide a strain-relief (since the plain soldered-on-only wires broke just in trying to install the pot, due to the thinness of the wire used; just not enough strands to hold up with that kind of bending). The tabs that used to hold the pot to the board are now bent around the sides, with a bit sticking out to grab the plastic shimming inside the handlebar. One reason this is not secured better is so that if the throttle gets twisted past the pot's endpoints, either by me twisting too hard in use (not likely) or by
accidentally twisting it too far while trying to catch the bike if it falls or something (I tend to go for the handlebar grips when this happens if I'm standing next to it while working on it, parking it, etc).

The only real problem with the throttle is that it has too much travel between fully off and fully on, nearly 3/4 of a turn. I am working on a way to reduce that to maybe 1/4 of a turn, so I can "gun it" easily when I need it, since rapid acceleration from a slow speed to a faster one without destroying my knees/ankles is one reason for having the motor--for those relatively rare traffic situations where going *faster* for a second is better than trying to stop.

Mostly, it's so I don't get run over from behind by an impatient or inattentive vehicle driver that's going too fast to stop in time, if *I* stop. Or even another cyclist, because I run across them every day that don't ride by the rules of the road but still ride on the road, in traffic. Those types don't generally stop for stop signs or red lights (or watch for other vehicles of any kind, including other cyclists, or pedestrians), and they one day will probably either cause an accident or be hurt or killed in one. More than one of them has yelled at me (as they go around me instead of stopping as they should) for stopping at a stop sign or red light, whether there is traffic oncoming or not. Months ago, one of them actually ran into the back of my bike, because he wasn't paying attention and expected me (as a cyclist) to just run the stop sign. He cussed me out and went on--I didn't bother trying to even respond to him, since if he's going to run stop signs and not pay attention on the road, there's not a lot of point in it--he probably won't live long enough to run into too many more cyclists. I try to lead by example, rather than by lecture, anyway, but I know it doesn't really work very well (probably better than the lecture, though, based on my very few discussions with other cyclists that don't follow the rules of the road, who either think I'm stupid for doing it (and should ride on the sidewalk instead, which is much more dangerous than the road, in my view), or actually get angry at me for trying to suggest that they'd be safer if *they* follow the rules of the road, which were created for the purpose of making a predictable, reasonably safe place to travel, which it is whenever the rules are followed by everyone at the same time: pedestrians, cyclists, and drivers).

Enough ranting; that's not why this blog is here (but I had to vent a bit, sorry). Suffice it to say that the capability is, if not absolutely necessary, very handy to have every now and then.

The only real issue with it is that I need better batteries. The ones I have are simply too old and abused to hold enough power for this application--they can put out serious power for a very short time (minutes, at best), where they'll actually keep me going at a pretty good clip (I still have to hook up the PDA speedometer again), but quickly fade to a lower plateau that does still help out, but won't push very hard or fast. The plateau is sustained for a while, maybe 3/4 hour or less, then fades out to unusable very fast after that. At least, based on my 10-mile-each-way trip this past Saturday, where this setup did prove quite useful in keeping me from overexerting myself at midday in the high-90's weather we had. I would not have made the trip successfully at that time of day without many more rest/watering stops on my own; it put the trip at about an hour and 20-something minutes, where it would have easily been 2 hours or more if totally under my own power, in that heat.

I also decided to add some anti-theft (and anti-spill) bars across the batteries, pop-riveted to the baskets to make it harder to just grab the batteries out and run with them, should a thief decide to try. Now, it won't stop anyone determined to get them, but it will slow them down enough that probably someone will notice them messing with the bike and maybe say something to someone. Might even slow them down enough for me to get back to the bike from whatever store I am in at the time (since it's only locked up outside when I go to stores and whatnot, places I can't take it inside with me).

One way to help improve this version of the drive system is to make the power I do have be used more efficiently, which since this is still a friction-drive system, will mean making the motor-shaft-drive-wheels smaller, from the about 3" they are now down to about 1.75", using roller-skate wheels. I may trim the wheels down to 1.5" or less, if I can do them symmetrically and easily. I picked up a set of used but good-condition non-inline skates at a thrift store for a couple bucks (tried to find some on Freecycle and with friends first, but no luck). I had first thought to find a skateboard for the wheels, but the thrift stores all wanted at least ten bucks for any they had, and with only 4 wheels per skateboard, and 8 wheels per pair of skates, well, the price-per-usable-part makes it an obvious choice. :-) Once I have the new drive-wheel setup worked out (since it requires moving the motors from in-line with the wheel to beside the wheel), I'll have a new post about that change.

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