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> Matt's Ev Bike Thread, Project log
johansen
Posted: March 29, 2012 12:35 am
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oh, i could make them blow up but i'm pretty confident that you can't make them blow up by just discharging them to -1 volt.

its REALLY easy to make them blow up via overcharge.
but that's not really interesting....



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AwesomeMatt
Posted: March 29, 2012 07:59 am
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QUOTE
but that's not really interesting....


*nod*, many times I find myself thinking "Oh, another explosion? *yawn*."

---

Found another few "sure glad I stumbled across that" tidbits today.

1 - Redirecting pulleys (actual pulleys, often not sprockets) for the drive side of the chain (the top, that carries the power) should be at least 3" large. Where pulleys or sprockets for the slack side of the chain (bottom) can use tiny ones. If you try to use small one on the power side, you'll shred it or or the chain.

2 - Heel strike. Probably obvious to everyone else, but I just noticed how easy it seems to be to design things poorly and end up having the front tire turn into the back of your foot when cornering, since the cranks are up front. In fact, on many commercial models that I look at, I can't see how it could possibly be avoided considering their design.

3 - The front derailleur needs a post welded to the frame above the crank to hold it up. It doesn't just float there magically. Also obvious, but the crank always hides it.

4 - The "new" thing I figured out about understeering is grossly simplified and maybe even incorrect. Reality is much more complicated. There's a tradeoff between maneuverability and stability (especially at high speeds). I can't tell if there's a difference between understeer and stability. If the way you get stability is understeer, or if understeer is universally bad and the way you get stability is similar but different. Arg. Important thing to nail down because it affects the angle I mount the front forks/head, which is the thing you only really want to risk welding once 'cause you could make internal parts mess up.

[Edited to confirm - It's a tradeoff. The amount of lead is called "trail" and it aids in stability but cuts from maneuverability. Increasing trail by altering the angle also benefits from reducing steering 'tilling' where you steel like a wheelbarrow because your handlebars are so far behind the axis of rotation. The more the axis is pointed at the handlebars the less tilling. Slightly higher head angle it will be!]


Hitting a scary point of "maybe I don't know enough to do this" at the same time as "dozens of hours of reading is enough, I'm not going to be in the mood to do anymore." Which means either I abort, or it's time to say screw it and just do it anyway and fix the screwups as I discover them. Option B it is. Less think, more do. I want to be riding this bike this season, not like my 4-year welder non-build.

Might as well wait until Eric's parts get here first though (tangent: he's been absent almost a week, longest I've ever noticed for him since I joined up here).

I have mostly decided to run single pipes to the seat, and then do triangular frame things behind that, for simplicity.

Freewheels are the only thing really scaring me but the good news is none of the rest of the bike depends on them. If I figure out/source them before it's time, great. If not, oh well, I'll go direct and ride it out until it bothers me.
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Jimthecopierwrench
Posted: March 29, 2012 01:55 pm
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QUOTE
[Edited to confirm - It's a tradeoff. The amount of lead is called "trail" and it aids in stability but cuts from maneuverability.
Not totally comfortable with your wording - where have you confirmed this?

The trade off should I'd think be in the effort required to move and maintain the steer wheel off ceneter - akin to automobile caster - with the weight at the bearing head attempting to straighten the wheel. Insane rake would indeed reduce overall maneuverability (for example turning radius) because you tend to flop the wheel over as opposed to pivoting the tread, As well, the more toward zero (vertical pivot) rake also increases tire wear as you scuff the tire about it's pivot axis - but - it's not a car, and the steering wheel rarely remains perpendicular to the surface in all but the slightest of turns.

I've seen chopper rakes that would not have allowed a 4 wheeled vehicle to even change lanes with a similar kingpin angle, and with the relative weight on the bearing head of a bicycle, surely only a pofessional Tour de France rider would notice any differences in steering effort.

My feeling is - and indeed no offence to taking the balls out weld it up and see if it kills ya source in mind laugh.gif - is shooting for, or just past the maximum end of a data selection of production rake angles and you probably won't go wrong.


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Jawno
Posted: March 29, 2012 03:28 pm
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Lots of good info on trail here:

http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry

I would recommend not changing the angle too much from a stock bike. Basically though closer to vertical will make a bike turn easier and further from vertical will make a bike track straighter. these effects vary some with speed too. A bike that has say 25 degrees rake will be hard to keep the forks straight at high speed. a bike with 45 degrees rake will handle great on the freeway but will be a bit hard to turn at 10 mph. this may be a bit of an exaggeration but you get the idea.
I vote for the "just do it" idea. Otherwise your gonna just have a pile of junk laying around demanding your attention. Sometimes things that seem like insurmountable problems have a tendency to just disappear once you devote some attention to them.
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AwesomeMatt
Posted: March 29, 2012 04:39 pm
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QUOTE
Not totally comfortable with your wording - where have you confirmed this?


*shrugs*. Honestly I've read probably 1000 articles by now on bike design and componentry, and should probably re-read 80% of them that I was only understanding 10% of at the time. I've started hitting the same ones I first found and picking up more like 40% on the second trip. Don't remember the source, wouldn't bet on me understanding it correctly either tongue.gif.

Wikipedia perhaps. Here's a good one. [Edited to add: while I was typing/drawing, Jawno found the same one, you win this time]. Also, "understeer" doesn't technically exist for 2 wheeled vehicles, another thing I read today somewhere.

And, since I last posted, now it's seeming that very little trail is more desirable.

Part of the difficulty of this whole process is separating wheat from the chaff. Bicyclers are optimization nazis and it's never really obvious whether they're arguing and insisting on variable ranges that have minutia hairsplitting improvements that are clouding my brain, or whether it's something big like "Put the seat far enough forward or your knees will clip the handlebars", another should've-been-obvious thing I just came across.

My flush check lately has been "if it's big enough to argue about, it's insignificant enough to not matter either way." It's the obvious stuff no one's arguing about that no one's really written anything about, and that's the stuff I need.

Also, I'm looking for comfort over performance, (at least compared to them) and people don't argue about what's comfortable, they argue (and buy) what performs better.

Something like "What's a comfortable seat angle that I could ride at all day?" is impossible to find. There's just debate over whether 22.1' or 22.3' is more aerodynamic and whether it's net beneficial to have to view between your ankles as you ride.

QUOTE
- is shooting for, or just past the maximum end of a data selection of production rake angles and you probably won't go wrong.


1 - I'm trying to. It's remarkably hard to find data. Mostly I've ended up looking for side-profile pictures, opening images in paint, drawing selection-boxes to count pixels and cross-multiplying to find sizes. At least tire sizes are standardized enough to reference.

2 - Recumbents especially are expensive and bought by performance fascists. "Minor" complications on an $8000 bike will include "pedals must be in perfect unique position while turning or they collide with the wheel". On the far end are the grandpa builders, building long wheelbase 10' long rickshaw-looking things with something the size of a lawnchair for a seat to park their fat asses in. No middleground.

Bicycle rake isn't adjustable for me since I'm using front suspension, I can't bend those bars, (FYI, "rake" for bicycles means dropout bend/offset, whereas on motorbikes it refers to the head angle, bonus confusion). I'm stuck modifying head angle only.

Honestly though in the time it takes to chop a wrong weld, clean it and weld it again, is about as long as it takes to read an article or two.

...

Didn't know you read the Home Made Projects sub-forum, can't recall you ever having commented on anything here.

...

Insisting on decisions and progress for tonight has yielded:

1 - 47" wheelbase unless I decide otherwise. Too many opinions. Don't care.

2 - On an upright my seat height was 39" and my head height was 68". My new seat height will be 20-23", and ride height 46-49". 19" lower than before. Great. It might be easier to pedal.

3 - My ass-to-heels measurement is 45". This helps decide crank-seat distance.

4 - Crank radius is 8". Worst heel radius on crank is 13". So, wherever I mount the crank has to be 13" away from the front tire/fender. This helps figure out the lowest front frame angle or length forward of the handlebars.

5 - I'm not screwing with a chainline that could strike the wheel. I'll raise the seat up a foot if I have to, which I won't.

6 - Seat angle no less than 34' (view/chin-chest annoyance) and no more than 52' (is apparently uncomfortably upright to pedal with feet forward). 40-ish sounds fine. Whatever.

7 - I might be able to arrange for the rear suspension to pivot *at* the motor drive output using my own bearings. If so, no chain stretch issues when the suspension compresses on a bump. If not, maybe screw with chain stretch idlers on the upper chain on the front (human-powered side). If not, oh well, no rear suspension, hope the batteries and motor don't snap if I hit a bump.

8 - If I end up just using the drill gearbox as is.. I'm leaving the chuck. I'll carry a damned chuck key and this will be my clutch if I can't find/build this double-opposing freewheeling system that no one's got the hang of yet. If the batteries die and I don't want to crank over the motor while pedaling, I'll just loosen the chuck a bunch so I'm only spinning the 90' outboard gearbox prop Eric's sending and not the geardown/motor. Shouldn't be too often an occurrence anyway. One extra freewheel only to coast pedals under motor power simplifies a lot.

9 - No such thing as low-ish upright seat and low crank. Puts your crotch up near the steering pivot. Can't slide it all back, because then crank then runs too close to the tire and there's heel strike. If you want to move back, the crank has to move upward arcwise around the 13" clearance to the front wheel. Will settle for higher crank rather than lower seat angle or larger seat height.

All together... torso is scaled small, but otherwise measurements check out for something like this:

user posted image

Purple is cargo rack/paniers and batteries. Green is motor. Dark green is reduction gearbox. Bluegreen is 90' gearbox. Handlebars are screwy 'cause I only had distances not angles and chose for distances to be exact while I eyeballed, and handlebars were drawn last.

Rear wheel isn't perfectly rotated, things will shuffle, didn't draw chainlines, but.. good enough for me to see that everything will work out.

Whew, thread was lacking for pics, even if hand-drawn.

[Edited to add so I'm not double-replying]:

QUOTE
I would recommend not changing the angle too much from a stock bike.


Yeah, apparently this is one of the things that the geometry is actually quite sensitive to. Everything is between 70 and 74' which covers from the sportiest to the cruiserest. Fractions of a degree make big changes in trail and have big impacts on handling.
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MacFromOK
Posted: March 29, 2012 05:14 pm
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QUOTE (Jawno @ March 29, 2012 09:28 am)
I would recommend not changing the angle too much from a stock bike.

Ditto. I've only ridden one raked front-end a few times (friend's Harley sportster), but it removed any desire on my part to own one... biggrin.gif


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MacFromOK
Posted: April 01, 2012 01:46 am
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QUOTE (AwesomeMatt @ March 29, 2012 01:59 am)
Might as well wait until Eric's parts get here first though (tangent: he's been absent almost a week, longest I've ever noticed for him since I joined up here).

Emailed Eric a bit ago and he's been sick for a few days, but is recovering now and should be back in circulation before long. beer.gif


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AwesomeMatt
Posted: April 01, 2012 02:34 am
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As did I. The poison failed. We'll have to think of something better next time.
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tekwiz
Posted: April 01, 2012 10:43 pm
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QUOTE (AwesomeMatt @ March 28, 2012 02:28 pm)
Yeah, I had read about the copper plating. Which was one of the reasons to never recharge if discharged below +1V.

Thanks for doing the experiment. Sadly nothing blew up.

Off and on, I forget how batteries would ever see a negative charge put on them. At the moment, I am currently forgetting how again.

In other news, I checked out my local hackerspace yesterday. Lots of guys working in offices. One guy hauled in 20 PCs with at least 19" LCD monitors and said they were free to a good home. They said people who couldn't afford a computer since they were "old" (probably still twice as fast as my best). However, it did give me the idea to ask everyone for their office's laptop batteries rather than send 'em to the recyclers. Will have to check in on that next week.

You get reverse charging when one or more cells has a lower capacity than the rest, & therefore goes dead while the rest are still in use.


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Fortuna favet fortibus.
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AwesomeMatt
Posted: April 07, 2012 02:06 am
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Not much of an update, but, my probably-useless diodes arrived this week:

user posted image

Posting for motivation's sake moreso than 'cause it's significant.
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tekwiz
Posted: April 07, 2012 08:42 pm
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QUOTE
1 - I'm trying to. It's remarkably hard to find data. Mostly I've ended up looking for side-profile pictures, opening images in paint, drawing selection-boxes to count pixels and cross-multiplying to find sizes. At least tire sizes are standardized enough to reference.


There's nothing wrong with this. I do it myself to obtain data, sometimes going as far as printing a pic out so I can measure parts of the image & scale sizes & geometry. Even better if there is something you are familiar with in the image, for then you can get actual sizes.

I've got your parts packed & addressed. I just have to drop the package into the mailbox, which I will do today or tomorrow.


BTW: It looks like you have the gearbox size pretty close in your sketch.

Also, avoid V bnelts like the plague. They are very inefficient, big, & clumsy. Chains should be your drive of chioce, with cog belts if you can't get chain hardware the right size. V belts are only a little more than 80% efficient. Cog belts are much better, but can't compare with chain drive, which is more than 97% efficient. Note also that you can exceed the size limits you mentioned, as long as you're willing to accept a lower lifespan. For example, I use a 1" aluminum V belt pulley on the last, high torque, stage of the drive in my bandsaw. It works, but I have to replace the pulley every year or so, as they wear down enough to break by this time. I suppose a stainless steel pulley would last much longer, but I haven't been able to locate one.


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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AwesomeMatt
Posted: April 07, 2012 10:17 pm
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QUOTE
I've got your parts packed & addressed. I just have to drop the package into the mailbox, which I will do today or tomorrow.


Hurray. Weather's improving enough that when I get over the Russian Death Flu I've contracted I can start molesting recycling centers and grabbing their batteries.

I wonder if there will be heat issues with the gearbox, since it was designed to run underwater. I guess I'll find out.

QUOTE
BTW: It looks like you have the gearbox size pretty close in your sketch.


Yeah, you had a lighter with it in your pic, so I knew the ballpark size. Doesn't matter much for precision, the sketch was for the frame lengths and angles, drawing the motor in was an afterthought.

QUOTE
Also, avoid V bnelts like the plague. They are very inefficient, big, & clumsy. Chains should be your drive of chioce, with cog belts if you can't get chain hardware the right size.


No need for belts at all. Most guys need a dual-stage belt-driven geardown because their RC motors spin so damned fast. But mine doesn't. Disadvantage of chain is high noise at high speed. A buddy of mine has a toothed belt driven single speed bike, and it's utterly silent. I don't need silence, but I don't want loud chain noise. Shouldn't be a problem compared to even just air noise.

Some math:

Motor top continuous speed: 3200 RPM (battery voltage is high enough to overdrive it to around 5000).
Drill gearbox: 38:1 dual-stage.

That gives me 84 RPM. A good cadence for a full size crank on the big chainring down to the tiny cassette sprocket at 30km/hour (or whatever the math works out to). But, not for 50km/h (30mph) top speed on a 3" drive sprocket rather than 8" or whatever a normal chainring was. I'm looking at double the speed and 3:8 the sprocket size. So, I'm 5.3 times too slow. I can't make the small rear sprocket any smaller, and I don't want to make the chainring any bigger, (fits under the seat) so I have to make the motor speed faster I guess. To undo 5.3x of geardown, what I will probably end up doing is removing one of the stages of the drill's gearbox (probably split evenly around 1:6 each, so, that'll give me 6x RPM back).

That, of course, unless the propeller gearbox isn't 1:1.

What would be perfect is if the prop gearbox was internally around a 6:1, then I could scrap the drill gearbox entirely.

Either way, sufficient geardown isn't an issue.

---

One thing I'm on the fence about is what size to make the front (pedal-powered) chainrings and/or what ratio to have the freewheel sprockets at. I was planning on just a simple 3" sprocket from the pedal chain, and a 3" drive sprocket for the motor chain.

The problem is I have to choose between helping the bike move at high speed (extending battery life and getting some exercise), or being able to pedal the bike at all if the batteries run out. I would need a huge chainring to not be silly-spinning my legs trying to keep up to 50km/h... but if I do that, what happens when the batteries are dead and I have to haul me and a 70 pound bike up a mountain to the next town, at maybe 10km/hour?

Obviously, one could say I should have two+ gears, big and small.. but you can't have that much variation between sprocket sizes because the chain tensioner can only pick up so much slack. If you drop from a 12" to a 5", you've got 10" of chain slack. Not feasible.

One option is for me to have only a single huge chainring on the front by the cranks. No gears. The use the front gear changer to switch among the different gears under the seat.

So the rear tire gears will be normal and switchable. The motor gear under the seat will always be 3". Next to it a second rear-casette with derailleur, and no gear switching at the crank. Small gears have less slack problems when changing among them because their circumferences are relatively small compared to the size of the chain tensioner.
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tekwiz
Posted: April 08, 2012 06:37 pm
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The gearbox has a slight reduction, I'm not sure how much...under 2:1, though.
I doubt heat will be an issue, as you won't be using full power all of the time & the GB has quite a bit of exterior surface to lose heat from. It might get warm, but it won't end up smoking hot.
In case I forget, EP-90 is the correct lubricant & it should be around half full.


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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AwesomeMatt
Posted: April 13, 2012 07:14 pm
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QUOTE
The gearbox has a slight reduction, I'm not sure how much...under 2:1, though.


It right at 2:1 actually, just arrived in the mail.

QUOTE
In case I forget, EP-90 is the correct lubricant & it should be around half full.


Did you ship it dry btw?

It's very, course and rattles when I turn, unless I keep it vertical and also lift on the input shaft. If I let the input shaft fall, it usually still turns but sounds like gears are grinding badly. I imagine it would wreck the gears in minutes if I actually powered it like this.

Keep in mind I've never really played with differentials or anything like this before, so I don't know how much of this is normal.

user posted image

A lot smaller than I thought it would be for some reason. About half the size/weight. That's convenient.
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tekwiz
Posted: April 13, 2012 07:27 pm
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I didn't drain it, but I also don't know how much is in there...check before using.
The input shaft has no bearing in the GB, only a seal. Therefore, you are going to have to join the shaft with your motor shaft & use the motor bearings to keep the shaft in alignment. The easiest way to do this would be to fasten the entire gearbox to the motor, or both solidly to the frame. The correct position is where it turns the smoothest with minimum backlash. The gears can be in contact, but with no pressure pushing them together.


BTW:That piece of aluminum tubing is part of the original mount & fits into the clamp at the top of the GB.


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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AwesomeMatt
Posted: April 13, 2012 08:10 pm
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QUOTE
I didn't drain it, but I also don't know how much is in there...check before using.


Ahh, it's half full or so.

QUOTE
The input shaft has no bearing in the GB, only a seal. Therefore, you are going to have to join the shaft with your motor shaft & use the motor bearings to keep the shaft in alignment.


Ahh, I see. Looks actually like neither shaft has a bearing. Tilt-alignment seems pretty easy, but depth-alignment will be much trickier. I'll have to experiment.

So, the motor might be a little bit overpowered. Bit of a difference in shaft sizes here...

user posted image

And the "completed" driveline:

user posted image

Too much geardown as is. I'll have to remove, at least, one of the drill geardown stages.

As-is, with all 4 stage geardowns:

3200 RPM @ 130V.
90' gearbox is 2:1 so 1600 RPM.
The drill is 38:1 so 42 RPM
The drive sprocket will be ~3" and the rear cassette varies from 4.5" to 2.5", so, between 1.5:1 and 0.8:1, so between 28 and 53 RPM.

The rear wheel is 26"=0.66m or 2.07m circumference, so between 3.48-6.69 km/hour. Or, between a slow and a moderate walking speed.

Kill one of the 6:1 geardowns in the drill gearbox.. 21-41 km/hour. Not bad. And if I use 170V instead of 130V like it's supposed to.. 27.5-53.7 km/hour.

Still a bit weak. I'd like a max speed a bit higher than that, batteries will drain too, so, maybe I'll upgrade to a 4" drive gear and increase those numbers by 33%.

Hrm, let's see if I get rid of the drill gearbox entirely, but pulse it on average at 130V still.. 126-246 km/hour. Nope. Guess not.
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tekwiz
Posted: April 13, 2012 08:17 pm
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What's your desired wheel RPM? The last powered bike I built had a design RPM of 350 at top speed. To get that using only motor & the GB I sent you would require a ~4:1 further reduction. This is doable with bike sprockets, even if you have to use a tiny idler on the GB output shaft. This with an original 6 speed back wheel gearing should give you a nice range of top speeds, suitable for differing terrains.


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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AwesomeMatt
Posted: April 13, 2012 08:38 pm
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QUOTE
What's your desired wheel RPM?


I dunno, I figure, 25-75 km/hour, so.. *maths* .. 200-600 RPM.

And, this is just physical gearing without any electronic speed control. I can go slower with the ESC but not faster.

I figure my average top speed will more likely be around 40 km/hour, but, I would like to have a higher max speed if situations call for it. Passing, running away from angry bears, getting to a cross-street before a sleeping driver wings me or a gravel truck passes me. That kind of thing.

The voltage will be 170V but will sag to ~115V when the batteries are nearly dead.

I'm happy with a 4" drive sprocket. That gives me 37-71 km/hour (22-42 mph) with full batteries. Electronic speed control can lower that down for city use.

Option B would be to go with a 3" drive sprocket (or slightly smaller), no drill gearbox, and use a 25% duty cycle or whatever it would need to be.
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AwesomeMatt
Posted: April 14, 2012 08:19 am
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I fired up the motor at 170V for the first time today (rectified & smoothed power cord from the wall). Does not sound too healthy. A bit scratchy sounding. Annoyingly high pitch. I hoped it would be rather quiet but it's actually a bit annoyingly loud for an electric motor indoor. I don't know what I was expecting, I guess a brush motor to purr like a fan induction motor.

It was spinning at ~4250 RPM.

After about five minutes I shut it down (takes only 4 or 5 seconds to drift to a stop... is that bad?). I put my fingers inside on the commutator and it was warm/hot, but not too hot to press and hold..

So I thought, maybe just rig up a series/parallel switch and drop the voltage after charging down to 85V. That'd quiet it up a bunch and cut the RPMs to 2125.

And then I thought, that's no different than PWMing the speed down. So, I could just do that. But then I thought about my current Plan A setup and the max speed of it requiring full motor speed.

Then I considered scrapping any kind of electronic speed control entirely and going with a relay. Pedal up to whatever speed my lowest gear will take, then toggle power on. Should be smooth, then use gearing to control speed. The only part of the project I don't have parts for and also don't know how to make, is the speed control with its mosfets, drivers, etc. Half tempted. 75% tempted as a trial.

Can anyone think of any issues with PWMing really low, say, 5-20%? And what frequencies I should run at? All else equal, I'd rather control speed that way 'cause it gets me the most variable range with the least audio noise.
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johansen
Posted: April 14, 2012 08:36 am
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increase the pwm frequency until the current ripple is about 10% of motor current.


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tekwiz
Posted: April 15, 2012 05:33 pm
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You also have to take total available power into consideration. That motor will reduce in speed depending on load. Use insufficient voltage & this drop in speed with load may become too much for successful operation. I think your best bet is to design for a maximum as per the motor's rating panel & your design top speed. Then you'll have to build the mechanics & do a short full power road test to see if you get enough accelleration. Then build your battery voltage & controls to match.
There are advantages in limiting the reduction stages to the bare minumum, as each extra stage means additional power loss.


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To him, mere toys of the moment, to be overturned at the flick of a finger.

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AwesomeMatt
Posted: April 15, 2012 08:48 pm
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So I'm going back over old comments..

Johansen recommends 10 (well 7 and 3 when charging) of these MOSFETs.

But the specs on them say each is 250V, 45A.

So, obviously I've never done this before and don't know how to think about it properly, but, at 170V I'll be drawing perhaps 3-15A. ~400W for legal speeds, 2500W for brutal uphills at inappropriate speeds.

So why wouldn't a single MOSFET suffice? Inductive surge every switching?

I'll trust what anyone says, but how do you know how much overkill is sufficient? (In this case, a single seems to be 3x overkill, and 7 is recommended, so 21x).

Also, jack up frequency until it's 10% of motor current... how do I know/calculate that?

And I also need a $4 gate driver. Sure, how/what/where?

On one hand I'd like to not have everyone just design this for me, on the other hand, I don't really know where to begin and any steps I do take myself lead me in the wrong direction.
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AwesomeMatt
Posted: April 27, 2012 03:13 pm
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Pushing to get something done on this, been 2 weeks. Mostly have been stuck on the gear ratio thing and not knowing what direction to take it. This, in turn, has been holding up any frame fabbing 'cause I don't know what will have to go where yet.

Progress:

- Stripped about half of the red (little, front) bike. Started at the back since I'm using the front as-is. Might use the rear gears/derailleur under the seat at the drive gears. Will use the (nice) brakes). Chain was great. Filmed it for video later maybe.

- Stripped about half of the blue (big, rear) bike. Rear gears are in great condition, long teeth and durable, they don't make them that way anymore. Rear tires are nice and fat, good for the weight. Left the rear as is and stripped from the seat post down. Tossed the crappy cantilever breaks. Kept the chain and front derailleur. Yanked the cables out, will re-use. Seat post came with a handy trailer mount. Filmed it too.

- Got a chain breaker tool and figured out how to use it. Harvested 4 chains so I'm probably good for those.

- Sent an email to the ERA about reusing their junk laptop cells, no reply yet.

- Grabbed a couple dozen bearings from inside industrial copiers, none fit any of my shafts though.

- Took apart an old almost-junk grinder after I realized they must have 90 degree gearboxes in them, (it does, 3:1) and considered using it instead of the propeller gearbox (2:1) if I never add another geardown stage. But I couldn't figure out how to take the damned thing apart any further than the back casing.

- Did a COSTCO trip on a hardtail (front shocks only) mountain bike and bought mostly canned goods (50 lbs worth). Threw them in the paniers and in a backpack and then kept my ass in the seat (no leg shock absorbing) up and down all curbs to see what 50lbs of motor/batteries and no shocks would feel like and how much fun it was climbing hills (what I'd be doing if the batteries died). Hills were manageable but I had to drop an extra chainring down. Square curbs are quite the crash down. Enough so I'm considering mounting the motor under the seat/top tube rather than behind the seat, to get some of the weight under the front shocks.


It's not much but, seeing bike frames that are a lot closer to being used was encouraging.


How easy/stupid would it be to make my own gearbox?

I'm stuck way too high (125km/h) or way too low (3km/h) using the 3 piece vs. 2 piece geardown. I need middle ground.

The drill gearbox has a ~5:1 and a ~7:1 set inside. I could extract either pair, but then I'd have to machine new holes and seals for them through the case and I'm not sure if this is stupid to attempt.

Then the drill has the chuck and all that bulk and I thought, what about just making a new gear box myself to house the gears? I don't know if that is the kind of thing that would be easy or if it's stupid to even suggest. Maybe just replace the drill box, or maybe chop all the way down to the 90 degree gearbox and replace the whole deal. Feasible/Stupid?

Waiting to buy a bottom bracket tool or return the gear puller I got for the purpose and buy a cheaper one that might fit (to pull the cranks off their square posts).

Just have to solve the geardown issue and then I'm ready to start physically building.
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tekwiz
Posted: April 27, 2012 06:42 pm
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I would use the motor & the 90 gearbox, & do the rest with sprocket sizes on the final drive chain.
Build your mechanicals first, testing them with a simple manual momentary switch.
Worry about the electronics after the mechanicals are functioning correctly.
Consider getting an arc welder, if you don't already have one. Trying to do what you want without welding is 10x harder.


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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AwesomeMatt
Posted: April 27, 2012 08:14 pm
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QUOTE
I would use the motor & the 90 gearbox, & do the rest with sprocket sizes on the final drive chain.


Can't. Not if I want to actually use the rear gears. Which, if I have good electronic control won't be an issue (tiny motors need geardowns for hill climbs, mine won't). But it will be an issue if the batteries ever die on me or there's an electrical problem and I have to pedal it to the next town, maybe through hills when it's geared for 50-75km/h. (If you can hit 50 and maintain it for 3 seconds, you have a bright future on a pro racing circuit).

Now, if I tried to use a set of big chainrings instead of the cassette on the back, I'd have chain drag issues because there is only so much slack the chain tensioners can pick up.

QUOTE
Build your mechanicals first, testing them with a simple manual momentary switch.


That's the plan. Actually half considering using only a relay ever, just pedal it up to low gear speed, hit the trigger, then change gears from then on to change road speed. That I know how to do 100%, and have parts already for 100%.

QUOTE
Worry about the electronics after the mechanicals are functioning correctly.


The motor, without additional geardown, even in lowest gear will try to spin the rear tire, instantly, at 164km/h @ 170V. It'll snap the chain or taco the gears.

Electronic speed control is mandetory without adding a ~5:1 geardown in there somewhere.

From the biking forum feedback I've got, mid-mount (non-hub) motors are plagued by this issue. Even with electronic control, eventually everyone slips when adjusting the throttle and the corresponding torque crumples the chainrings.

QUOTE
Consider getting an arc welder, if you don't already have one. Trying to do what you want without welding is 10x harder.


I've heard most bikes aren't even welded, just brass brazed. But no matter. I have my TIG welder 3/4 complete (UGG, haven't worked on it in over a year, burnt out). I'll just power the transformer and FWB and bypass all the incomplete HFHV stuff. I already have a pack of 1/16" electrodes.

I'd really rather, if I could, use a second gearing box somewhere. It's just a matter of how feasible that is to accomplish and what's the best method to take.
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