Eric's Project #002

[Beagle123]

Neck Finished, Holes for Swing Arm Drilled

I visited the welder today. He added welds all around the inside of the battery box, and welded the top piece of the neck. I also had him drill nice 5/8th inch holes for the brass bushings for the pivot point.

The fit is really good. To get the bushing into the hole, you need to pound it with a wood block. I want a nice tight fit so the aluminum won't abrade from the friction, causing the joint to loosen-up (and further deteriorate).

The fit si so good that the friction alone would probibly provide a bond between the aluminum and brass. But I was thinking that I could epoxy the bushings in place. This would really bond the pieces together. That's how golf clubs are made--the head is epoxied to the shaft (good metal to metal bond). Another option is to put a few drops of thread-lock into the hole.

It all may be overkill, but I don't anticipate removing the bushings, so I don't see why not.

Opinions?

Eventhough I didn't actually do much work, I feel like a great deal has been accomplished because that poivot point was such an important detail. The solution turned out so well that I think I'd be happy if I got that one thing done in two days work. I would have hated to mess that part up and have to re-do it. or make a "work-around."

I think I'm in the "home stretch" now. THe rest of the building process should be easy. I think I can easily be done with the building process in a few days. Then I have to think about buying/making a battery pack. I'm not going to make a hasty decision on that though.

 

[Beagle123]

if i want to get a reasonable range i need to keep it at about 20 mph and at that speed the motor is running past the peak efficiency point too close to the no load area. with my new bike ill have a higher ratio(7.5 - 8:1) so that at top speed the motor is running at its max rated power and at about 20 mph its running at peak efficiency.

Hey dirty:

I have a current meter hooked up to my bike now, and I've noticed that it takes about 17-18 amps to maintain a speed of 20mph in 5th gear, and it takes about 13-14 amps to go 20 in 4th gear. Lesson: more Rpms = better. At some point I'll get the exact numbers and give them to you.

Also, I've noticed that when the motor levels out, it uses very few amps.

Another thing I"ve noticed is that when I'm accelerating there are certain "power bands" for the motor. It seems like the motor just burns amps wastefully until you get somewhat below the max efficiency point, then it "kicks in." When it reachess a certain point you can feel the acceleration pick up. For me, in 1st gear, my scooter is sluggish until it reaches about 6-7mph, then it accelerates nicely to 13mph, and then levels out. The best acceleration occurs when its going fast, and then you go faster. Then you hit the top point and it levels out at low amps. This might be the best way to ride: have it in low gear and "floor it."

 

[Beagle123]

just touch the leads to a 9V battery and watch the sprocket from the top to watch how much it wobbles,

...

, ive seen the 85-90t ones for $14 the 114t ones above $40.

I tried using a 9v battery, and yep it wobbled. Cool trick.

Where can you find 85-90 tooth sprockets? I found this one:

http://www.gokartsupply.com/sprocket.htm

But its 72 teeth. I need the 4 hole pattern with 2 7/8 spacing like the ones at the top of that webpage. I could go with 72 teeth, and use a 9 tooth sprocket too. That's 8:1

The threaded part is only sunken about 2mm. You can see a pic of the shaft on the previous page. It should grip if its the right bore.

 

[Miles]

Hi Beagle

I would us #219 chain and composite rear sprocket: http://www.pittsperformance.com/index.php?cPath=26_95_114

 

[dirty_d]

For me, in 1st gear, my scooter is sluggish until it reaches about 6-7mph, then it accelerates nicely to 13mph, and then levels out.

that must be your imagination, in a permanent magnet dc motor the torque is always greatest at 0 rpm and gets lower as the rpms increase.

i guess choosing the safe top speed ratio for a 1:1 ratio in the hub is ok, since you're using 22" wheels then the highest speed while staying at the motors rated power of 1200W would be about 34.4 mph at a overall gear ratio of 6.08:1 the highest possible speed. at the MY1020 1200W motors max output of 1900W(at stock voltage at 2000 rpm) the top speed would be 40 mph at a overall ratio of 3.27:1, but at an efficiency of 50% and at 60A. 8:1 would not be a good ratio for 22" tires.

since the tires are 22" you don't need such a high ratio from motor to rear sprocket, you can just choose the ratio so that you reach the highest top speed at the highest gear in the hub. since its 22" you probably only need about an 80 tooth sprocket to do this, if you tell me the highest gear ratio in the hub you're using i can tell you.[/quote]

EDIT: assuming the highest gear in the hub is .66:1 then your sprockets would need to be 10t on motor and 93t in the rear for a ratio of about 6.1:1 overall.

 

[xyster]

For me, in 1st gear, my scooter is sluggish until it reaches about 6-7mph, then it accelerates nicely to 13mph, and then levels out.

that must be your imagination, in a permanent magnet dc motor the torque is always greatest at 0 rpm and gets lower as the rpms increase.

But power is not greatest at 0rpm, and acceleration is a function of power (torque X rpms), not just torque. That's why overvolting improves acceleration. I've noticed the same thing as Beagle. My 5304/20" accelerates best from about 15 to 20mph. The curve used to be fairly sinusoidal with the 24" wheel. Perhaps overcoming initial inertia or cogging/stickiness plays a part in this.

 

[fechter]

The current limiting in the controller limits the torque at low speeds during acceleration. If you didn't have current limiting (or had a really high limit) it would take off much quicker.

 

[safe]

...and if you were to switch to an Inductance type motor the best efficiency occurs while under full load. That's the "problem" with the DC motor in general, the best efficiency occurs in a narrow rpm range up pretty high and it doesn't always coincide with the best power which is usually down a little lower. Gears are a "quick fix", but the real problem is the DC motors permanent magnets that force a powerband shape onto you that you don't really want. The "answer" is to create an Inductance hub motor for the electric bike... that would kill the need for gears overnight.

Go Tesla... the year 1887 rocks!

 

[Miles]

Gears are a "quick fix"

 

[xyster]

... Gears are a "quick fix",

Hallefreakinlujah, he's finally seen the light!

 

[safe]

Hallefreakinlujah, he's finally seen the light!

The future is simply to get out of DC motors and move into the realm of Tesla's Induction motor. And the ultimate is the modern Switched Reluctance motor that won't operate at all without a computer. That's REAL high tech and will in the end beat everything... at least it appears that way right now. (you never know what ideas might surface)

Gears are a tempory transistional stage for people who are "sport" oriented like myself. Those that want "steady state" operation are just fine with the DC motor because holding a constant speed is what DC motors do best. Gears are a halfway measure to get to the Induction motor. DC motors and gears are also cheap and available... so sometimes it comes down to price.

I just think the ideal of a completely computer controller motor down to the actual firing of the coils is really cool. That would mean you could program the bike for a specific track or possibly to comply with certain laws. The idea of moving the control logic out of the physical realm and into the software realm seems like really good thing to do. You have to remember I was a computer programmer once and like the idea of blending the computer field into the electric bike field.

 

[dirty_d]

the only two things that determine acceleration are force and mass, it is true that in order for a wheeled vehicle to accelerate the wheels must be spinning but torque and only torque at the wheels determine what the acceleration will be. power has nothing to do with it unless its divided by the speed.

 

[xyster]

the only two things that determine acceleration are force and mass, it is true that in order for a wheeled vehicle to accelerate the wheels must be spinning but torque and only torque at the wheels determine what the acceleration will be. power has nothing to do with it unless its divided by the speed.

I don't remember enough physics to explain it myself. This is the best plain english explanation I could quickly find:

http://www.madsci.org/posts/archives/2005-05/1115165795.Eg.r.html

Hi,

Many people are often confused about power and energy.

Let's start from the beginning, with some basic equations:

Energy = Force * distance

For a mass m moving at a speed v, the energy E is:

E = 0.5 * m * v * v

Energy can be measured in Joules (J) or British Thermal units (BTU). 1 BTU is equal to roughly 1055 Joules. If a 2100 pound car is travelling at 60 miles/hour, the energy is about 342600 Joules or 325 BTUs. This is the same amount of energy required to accelerate the car from 0 to 60 miles/hour on level pavement. This is independent of acceleration, it doesn't matter if it takes 6 seconds or 60 seconds, it's the same amount of energy.

Energy is always conserved, meaning it can't created or destroyed, it can only change form.

Power = rate of energy

Power can be measured in Watts (W) or Horsepower (HP). 1 HP is the same as 746 Watts.
....
Since we know power is the rate of energy, we can divide the energy calculated above by the time required to produce the energy. If it takes your car 6 seconds to go from 0 to 60 miles/hour, then the power is about 57000 Watts or 76.6 HP. Keep in mind, this is the average power, it doesn't tell us the power at any time during the acceleration. We would need detailed speed measurements from start to finish to calculate that.

You can see the effect of additional voltage on acceleration with the 4qd calculator:
http://www.4qd.co.uk/faq/current.html
For any given acceleration, halving the voltage requires doubling the amps (because acceleration is a function of power, not torque).

 

[safe]

the only two things that determine acceleration are force and mass, it is true that in order for a wheeled vehicle to accelerate the wheels must be spinning but torque and only torque at the wheels determine what the acceleration will be. power has nothing to do with it unless its divided by the speed.

Power = Torque * Rpm

...so:

Torque = Power / Rpm

...in actual units we would add a constant:

Torque (Nm) = Power (Watts) * Radians-to-Rpm-Constant (9.549 but we can call it 10) / Rpm (a number)

So to get 10 Nm of torque at 1000 rpms we need:

10 Nm = X Watts * 10 / 1000

10 Nm -> 1000 watts of power required @ 1000 rpms.

But let's change the rpms so that they are doubled:

10 Nm = X Watts * 10 / 2000

10 Nm -> 2000 watts of power required @ 2000 rpms

At this point we're going "what the heck?" I'm increasing the rpms and it seems like the more I increase the rpms the more power it takes to get the same torque. But wait... we've forgotten final gearing. What happens when we account for the gear ratio from the motor to the rear wheel?

In the first case let's assume a gear ratio of 1 to 1:

So 10 Nm takes 1000 watts of power @ 1000 rpms and this produces 10 Nm of torque at the rear wheel.

In the second case let's use a gear ratio of 1 to 4... in other words the front motor side sprocket is small and the rear sprocket is large.

Final Torque = Initial Torque * Gear Ratio

So 10 Nm takes 2000 watts of power @ 2000 rpms but we are now changing the gear ratio so that we quadruple the effective torque on the rear wheel. So now the rear wheel sees 40 Nm of torque.

Final Torque = Initial Torque * ( 4 / 1 ) = 10 Nm * 4 = 40 Nm

(so we doubled the power, but we also quadrupled the rear wheel torque through gearing)

Let's say that we start with:

A 5 to 1 gear ratio.

2 Nm = X Watts * 10 / 5000

2 Nm -> 1000 watts of power required @ 5000 rpms

Final Torque = Initial Torque * ( 5 / 1) = 2 Nm * 5

Final Torque = 10 Nm !!!

Summary:

It's possible to take a motor that only produces 2 Nm of ACTUAL torque at the motor itself and if you run it at high enough speed and gear it down enough you can achieve a rear wheel torque that is 5 times larger than the motor torque.

This is the foundation for all motors and their gearing... you can mess around with torque by playing with the motors speed and it's gear ratio. The "re-rating" process (overvolting) is basically that you take an ordinary motor and increase it's speed with more voltage then gear it back down. The net effect is that there are "sweet spots" of optimum effiency that you can target. If you could know your motors true profile you could optimize your bike around it.

 

[Beagle123]

Hi Beagle

I would us #219 chain and composite rear sprocket: http://www.pittsperformance.com/index.php?cPath=26_95_114

Hi Miles: Thanks for the info. I already have the sprockets to use #25 chain. But I looked at what #25 chain looks so small and flimsy. I'm planning on running about 1200 watts (= 1.5 hp) so I don't imagine that would break the chain, but my concern is that since the pitch is 1/4 inch, it might flex around like a rubberband between the sprockets, and come off the sprockets.

I think this scooter chain is commonly used when the motor and the back sprocket are very close together. (See Pic). On my bike they will be about 14 inches apart. I don't know????

I could try it and see what happens too.

I never knew that #219 even exists. Is it stronger? wider? Its my understanding that it also has 1/4 inch pitch.

1/4 inch pitch chain just feels so tiny to me. It seems like the #35 chain is more substansial.

 

[dirty_d]

the formula for acceleration is acceleration = force/mass as you can see no speed or power involved, you can see there that torque(force) minus drag force divided by the vehicles mass are the ONLY things that determine acceleration. as your bike starts moving and the motor rpms increase and so does the power but NOT the torque and NOT the acceleration. for any gear ratio your acceleration will always be the greatest starting at 0 rpm and decrease as you speed up. ive already posted this before but there it is again the various properties of my bike torque, acceleration, efficiency. along with the code here you can see the acceleration only depends on the torque on the rear wheel.

e = 2.71828

#motor specific stuff
Vmax = 48.0 #operating voltage
R = .3 #winding resistance
K = .1145 #speed/torque constant(voltage / no-load speed(rad/sec))
Inl = 1.5 #no-load current draw
Imax = 170.0

#bike specific stuff
wheel_radius = .33 #meters
gear_ratio = 10.0
mass = 113.0 #(kg)
CwA = 0.51 #coefficient of drag times frontal area
Nw = 0.95 #motor to wheel power efficiency
P = 1.2 #air density (kg/m^3) 1.1 approx at 20C 1BAR

C = (P * .5) * CwA # this will be constant for all velocities(C * velocity^2 = drag-force)
Wnl = Vmax / K
Rm = R / (K * K)
Is = Vmax / R <Imax> 100 ? Imax : 100 + 10] #to give a little more room
set xrange [0:x1]
set y2range [0:1000] #to give a little more room
set ytics nomirror
set xtics nomirror
set y2tics 0, 100
set ytics 0, 10

Ia(x) = ((Vmax - K * x) / R < Imax ? (Vmax - K * x) / R : Imax) #perfect motor current
I(x) = Ia(x) + (Inl - Ia(x)  / Imax * Inl ) #account for no-load current
V(x) = I(x) * R + K * x 
T(x) = I(x) * K
P(x) = T(x) * x
Tw(x) = T(x) * gear_ratio
Vel(x) = (x / gear_ratio / (2.0 * 3.14159)) * (wheel_radius * 2 * 3.14159) * 3600.0 / 1000.0 #rads/sec to km/h
MS(x) = x * 1000.0 / 3600.0 # km/h to m/sec
N(x) = (1.0 - (Inl / I(x))) * (1.0 - (I(x) / (V(x) / R)))
F(x) = Tw(x) / wheel_radius #force on bike
D(x) = C * (MS(Vel(x)) * MS(Vel(x)))
A(x) = (F(x) - D(x)) / mass

Aavg(x) = (x <= 0) ? A(0) : A(x) + Aavg(x - 5.0) # find the average acceleration since until velocity 'x'
#Time(x) = MS(Vel(x)) / (Aavg(x) / (x / 5.0))
v_max = 11.1
a_max = 5.0
vt(x) = -v_max * exp( -a_max / v_max * x) + v_max

set x2range [0:10]
set x2tics 0, 1
set x2label "Velocity km/h"

plot  \
N(x) * 100 axis x1y1 title "Motor Efficiency", \
F(x) axis x1y2 title "forward Force", \
A(x) * 10 axis x1y1 title "Acceleration X 10", \
D(x) axis x1y1 title "Drag", \
vt(x) / 1000.0 * 3600 axis x2y1 title "velocity"

EDIT: oops had wrong labels on graph, fixed.

 

[xyster]

the formula for acceleration is acceleration = force/mass as you can see no speed or power involved, you can see there that torque(force) minus drag force divided by the vehicles mass are the ONLY things that determine acceleration. as your bike starts moving and the motor rpms increase and so does the power but NOT the torque and NOT the acceleration. for any gear ratio your acceleration will always be the greatest starting at 0 rpm and decrease as you speed up.

For constant acceleration, doesn't 1/2 MV^2/t = force/mass?

http://downloads.openchannelsoftware.org/HEVA/docs/appx_a.html

A-4. Power Required for Vehicle Acceleration

The following equation calculates the power requirement for vehicle acceleration, represented by the variable Paccel.

Paccel = Vave MGr.Veh. a ,

in which Vave= average velocity = 1⁄2 (V2 + V1), and

a = acceleration = deltaV/deltat (m/s2).

http://www.4qd.co.uk/faq/current.html

 

[dirty_d]

thats for solving average acceleration for a known velocity and known time to reach that velocity, the instantaneous acceleration is found with force/mass.

 

[TylerDurden]

The "re-rating" process (overvolting) is basically that you take an ordinary motor and increase it's speed with more voltage then gear it back down.

Not.

"...the motor’s performance is extended through a reduced voltage re-rate procedure. This yields an extended full-flux regime that permits a given motor to achieve full rated torque and much higher power as its speed range is extended."

"Consider a machine intended for operation up to 100 Hz, 200 V three-phase RMS, 100 N-m rated torque, 6 poles, 2000 RPM base speed, 21 kW output, and a 3:1 field weakening range. If the stator winding taps are rearranged to provide a 66 V rating (low-voltage delta connection) instead, and a source capable of delivering 200 V at 300 Hz is available, this same machine can be re-rated for 300 Hz, 200 V, 100 N-m, 6000 RPM, and 63 kW output power without field weakening ratings violations."

This is not simple overvolting. If that's the only way you can understand it, fine. But trying to convince the rest of the world that it is simple overvolting is pathetic.

When you've got a patent in your hand instead of a brewsky, you might gain some credibility. Even then, Chapman will have ten to your one. That's why he's rolling in Gibralter bullion and you're stuck in Missouri with blueballs.

 

[Miles]

Hi Beagle

I would us #219 chain and composite rear sprocket: http://www.pittsperformance.com/index.php?cPath=26_95_114

Hi Miles: Thanks for the info. I already have the sprockets to use #25 chain. But I looked at what #25 chain looks so small and flimsy. ........

I never knew that #219 even exists. Is it stronger? wider? Its my understanding that it also has 1/4 inch pitch.

1/4 inch pitch chain just feels so tiny to me. It seems like the #35 chain is more substansial.

#219 chain has a smaller pitch than #35 (.306" - circa 7.8mm) but can be got in a similar strength. It's used for go-karts. For our purposes, I think its better than #35 because smaller pitch equals smaller sprockets and slower linear chain speed - also, you can only get the Extron composite sprockets in #219 size.

I expect #25 will "work" but, as you say, it looks a bit unsubstantial and it will probably wear (stretch) more quickly. I don't have any experience of using it, though... maybe someone else could comment?

Ref:

http://www.tsracing.com/Techtips/TSchain.html

http://www.azusaeng.com/chain/krtchn.html

 

[Beagle123]

I think its better than #35 because smaller pitch equals smaller sprockets and slower linear chain speed - also, you can only get the Extron composite sprockets in #219 size.

Thanks Miles: I agree with everything you said, but here are my problems:

1) I'd have to make some kind of adapter to attach that 90 tooth sprocket to my freewheel. Or, I'd have to figure out how to attach it to another freewheel. My bike has a standard 1 3/8 threaded hub attachment.

I bought one of these:

http://tncscooters.com/product.php?sku=203170

I have a 80 tooth sprocket for it (#25) I thought I could use it as an adapter for another sprocket (like your composite) by drilling holes in it. That's one potential solution.

2) I'd have to figure out how to attach a front sprocket to my motor. My motor has a 12mm shaft. The 1/2 inch bore sprockets don't fit quite right. dirty_d suggested getting a smaller bore sprocket and boring it out. I think that's a good idea. However, the #219 front sprockets I've seen have 3/4 inch bores. No good. I'm guessing that they're metric, so maybe I can find a #219 front sprocket with 12mm bore. That would be awesome.

Do you know of any front sprockets with 9-13 teeth or so?

 

[Beagle123]

Cut Pieces for Back End, Made Two Panels

I got a couple of things done today. I had to re-cut new pieces for the back diagonals. They look great. Its a bit tricky balancing tubes in 3 dimensions and marking angles. I probibly should have set it on its side to make it eassier, but I got it done.

The panels look really cool. Its my first look at what the body will look like when covered in tread-plate. I love how it looks. This tread-plate isn't just for looks, it adds A ALOT of strength. Its the same principal as sheer-wall in contstruction: if you frame a wall with just 2X4s it can be collapsed diagonally, but if you nail plywood onto it, nothing can break it.

The frame feels very strong even without it.

I found that the easiest way to make the panels is to cut them a tiny bit oversized, then clamp them into place, and sand the edges that stick-out with a sanding disk attached to my grinder.

 

[Miles]

Beagle,

That scooter freewheel really isn't up to much.....

Most of the #219 drive sprockets have a tapered bore - often 10 to 14mm. Maybe there's something suitable here? http://www.out2win.com/catalog/sprkt_eng.html

 

[Beagle123]

I found this one too:

<a href="http://cgi.ebay.com/ebaymotors/IAME-10T-219-Direct-Drive-Sprocket-BARGAIN-SALE_W0QQcmdZViewItemQQcategoryZ107068QQihZ007QQitemZ170124646318QQrdZ1QQsspagenameZWD1V#ebayphotohosting">sprocket</a>

No mention of size of bore. I'll research what "Yamaha taper" means. Anyone know?

Also, I know that freewheel is cheap. Someone wrote in about theirs breaking. But I don't know what else to do.

 

[Miles]

I would use one of these: http://www.whiteind.com/ENO-free-specs.html

The 22t version has weight-saving slots milled into it that you could easily bolt a custom adaptor to #219 spec to. That was my solution to the freewheeling cranks problem... :wink: