mattW's Electric motorcycle conversion Blog

Post up a thread for your EV. Progress pics, description and assorted alliteration
User avatar
Richo
Senior Member
Posts: 3536
Joined: Mon, 16 Jun 2008, 00:19
Real Name: Richard
Location: Perth, WA

mattW's Electric motorcycle conversion Blog

Post by Richo » Thu, 06 Nov 2008, 02:44

All seems excessive Matt.

Cheap local standard AC motors
Li-po batteries (400Vac)
Custom controller
Should do 0-100kph under 4sec.
More than that and you will be loosing traction etc etc..

So I don't see why you'd bother with excessively high voltage.
more expensive US motors.
Custom rewinds.
Custom high voltage controller.
You wouldn't be able to keep the front wheel on the ground.
Or are you trying for a high speed eV record?
Help prevent road rage - get outta my way! Blasphemy is a swear word. Magnetic North is a south Pole.

antiscab
Senior Member
Posts: 2323
Joined: Mon, 26 Nov 2007, 05:39
Real Name: Matthew Lacey
Location: Perth, WA

mattW's Electric motorcycle conversion Blog

Post by antiscab » Thu, 06 Nov 2008, 02:50

im thinking sports bike acceleration.
so being able to do 100-200 as fast as i can 0-100 (ie traction limited acceleration to 200).

i need high voltage for high rpm on a stock motor (no rewinds).

im liking the ev speed record :D
and y not....it is pipe dream territory after all

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

Rodney
Noobie
Posts: 18
Joined: Tue, 15 Jul 2008, 04:55
Real Name: Rodney O'Donohoe
Location: Adelaide, SA

mattW's Electric motorcycle conversion Blog

Post by Rodney » Thu, 06 Nov 2008, 04:14

Unfortunately the reality of the Laws of Physics may clog up your pipe dreams.

You can not simply apply a high voltage to a stock motor and expect to get more RPM, as the motor winding insulation will simply breakdown due to the higher voltage. Also the centrifugal forces increase with the square of the rotational speed. The other major problems are that the winding inductance will have a far greater affect on the motors impedance due to the higher frequency, along with other effects like more heating due to eddy currents in the laminations etc. Higher voltages also make the motor control much more expensive and unreliable. Also if you use a brushed motor, the higher voltages will cause a plasma flashover in the commutator destroying it very quickly.

Batteries have power/weight limitations, not current limitations. Therefore use higher AH batteries, or parallel them up, to keep the voltages reasonable, ie. less than 600 Volts, preferably much lower, otherwise the motor controller will be too expensive. If you are looking at drag racing, then consider super or ultra capacitors.

Motors also have power/weight limitations. You can change the voltage/current ratio by the winding design, however the power is essentially limited by mechanical factors, and magnetic material limits. Especially temperature limits, and the effects on the magnetic materials.

A PERM-132 motor is good for around 7KW continuous (about 100Km/hr) on a small motorbike, but can give around 30KW for a few seconds to quickly accelerate. In order to double the speed, you need 8 times the power, so you are looking at about 60KW for 200Km/hr.

Also at that insane speed, make sure you wheel base is long enough, and the weight forward enough, and definitely a spoiler at the front to keep that front wheel down.

Given that the range a 7 KwHr LiFePO4 powered motorbike is in the order of 150Km at 60 kph, I would keep your max speed down to 100kph as even at 100kph your range will drop to about 50Km (or 30 minutes). At 200kph your range would be about 13Km (or 4 minutes).

An interesting fact is my 200Kg 500cc scooter uses about 4.5 Ltr/100Km, whilst my 1400Kg Diesel car uses 5.5 Ltr/100 both around town. On the highway my car is actually more economical, despite its weight, due its far lower aerodynamic drag.

Given that batteries are the biggest cost of a conversion, it is actually cheaper to convert a car for highway use than a motorbike. Hence I have canned my electric motorbike project, sold the donor bike, etc.

I am still trying to decide if I should convert a new Toyota Yaris Sedan at a total cost of about $45K or wait for the Mitsubishi MIEV due late 2009 (around $30K I have heard).

Best wishes for your project, if you make some compromises on the top speed performance, you could have a realy nice quick bike that still does the state limit.

Rodney.

antiscab
Senior Member
Posts: 2323
Joined: Mon, 26 Nov 2007, 05:39
Real Name: Matthew Lacey
Location: Perth, WA

mattW's Electric motorcycle conversion Blog

Post by antiscab » Thu, 06 Nov 2008, 04:49

i would have suspected the motor winding insulation would have a degree of safe overload to them, were only talking 6x voltage. (around the overload we subject series wound forklift motors to).
i wonder how many hours of 6x voltage motor insulation survives for?
100hrs? 10hrs? even at 10...thats a long time of acceleration.
the motor only sees 6x voltage hard acceleration at 9000rpm (150kmh+)
not going to be a common occurance.

i remember tuarn saying something about bench testing a 2.2kw 4 pole motor at 9000rpm....tuarn how did that go?

in any case at 100kmh i was thinking more like 6000rpm, or less. i hadnt intended to keep the gearbox.

agreed, DC motors don't do high voltage, and i hadnt intended to use one for this project.

a 1400v 5AH pack of K2 cells, or lifebatts, or A123s, or any other high power cell, weighs 100kg, and max power of 100kw (100A at 1000v).
just need to use cells that are properly power dense, no TS for this.

magnetic limits affects torque density.
add rpm limit = power density.

just need to derate the continuous power, so 2.2kw at 4x = 7.5kw continuous.
might try and find a fatter higher power motor to fit...or maybe just two or 3 2.2kw units.

a perm-132 (at least on its own) doesnt have the kind of power im after (or the rotational speed?).

ive experienced first hand how un-aerodynamic bikes are. it takes so much more power to go just a little faster, even on my moped.
going from 55kmh reliablely to 65kmh reliablely was an extra 1.5kw.

i doubt its cheaper to convert a car than a bike (at least if your counting comparable performance).
my car conversion has cost me $35k so far, and still has another $8k to go. even then im only expecting 0-100 in 6-7 sec.

for the same money, id suggest i can get much more out of a bike (except for range of course).

13km would get me to work...in 4 minutes :D.

if i was after a bike with 30kw, id buy a vectrix and repeat my soldering copper across the shunt trick:p

as i say....well into pipe dream territory.

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

User avatar
Richo
Senior Member
Posts: 3536
Joined: Mon, 16 Jun 2008, 00:19
Real Name: Richard
Location: Perth, WA

mattW's Electric motorcycle conversion Blog

Post by Richo » Thu, 06 Nov 2008, 04:51

Rodney wrote:Also if you use a brushed motor, the higher voltages will cause a plasma flashover in the commutator destroying it very quickly.
Sorry we are talking AC induction motors so no brushes.
For what Matt wants he will need a rewind for better insulation for high voltage.
Rodney wrote: Batteries have power/weight limitations, not current limitations. Therefore use higher AH batteries, or parallel them up, to keep the voltages reasonable, ie. less than 600 Volts, preferably much lower, otherwise the motor controller will be too expensive. If you are looking at drag racing, then consider super or ultra capacitors.
Actually the limitation will be the internal impedance.
This will dictate your peak power from the batteries.
It also dicates the heat generated in the battery thus the "C" limitation.
Higher Ah is not required plenty of Li-po batterys suit an AC bike.
For an ACIM controller 1200V devices are the norm so 600V bus is fine.
Higher voltages are not a problem plenty of devices to choose from.
Caps will lower the internal impedance thus increasing peak power.
But not really required for sub 100kW.
Batteries can cope just fine - even a 6Ah li-po will do it.
Rodney wrote: A PERM-132 motor is good for around 7KW continuous...
Yeah they are too small for the performance we want.
And expensive.
Only + for it is the size.
Rodney wrote: Given that batteries are the biggest cost of a conversion, it is actually cheaper to convert a car for highway use than a motorbike.
I seriously doubt that.
Your numbers must be out by about a factor of 3.
Rodney wrote: Best wishes for your project, if you make some compromises on the top speed performance, you could have a realy nice quick bike that still does the state limit.


Yeah Matt don't forget the speed limits.
Help prevent road rage - get outta my way! Blasphemy is a swear word. Magnetic North is a south Pole.

antiscab
Senior Member
Posts: 2323
Joined: Mon, 26 Nov 2007, 05:39
Real Name: Matthew Lacey
Location: Perth, WA

mattW's Electric motorcycle conversion Blog

Post by antiscab » Thu, 06 Nov 2008, 04:53

oh....and i might need a pipe dream dyno to go with my pipe dream motorbike...
gotta bench test motors to desctruction.

lol....i think ive hijacked Matts thread, sorry matt.
shall i make a new thread?

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

User avatar
Richo
Senior Member
Posts: 3536
Joined: Mon, 16 Jun 2008, 00:19
Real Name: Richard
Location: Perth, WA

mattW's Electric motorcycle conversion Blog

Post by Richo » Thu, 06 Nov 2008, 04:55

antiscab wrote:might try and find a fatter higher power motor to fit...or maybe just two or 3 2.2kw units.

3 is the magic number Image
Help prevent road rage - get outta my way! Blasphemy is a swear word. Magnetic North is a south Pole.

User avatar
Richo
Senior Member
Posts: 3536
Joined: Mon, 16 Jun 2008, 00:19
Real Name: Richard
Location: Perth, WA

mattW's Electric motorcycle conversion Blog

Post by Richo » Thu, 06 Nov 2008, 04:57

Well it would be nice if he got back to us on some updates on his conversion.

Some measurement would be nice...
Help prevent road rage - get outta my way! Blasphemy is a swear word. Magnetic North is a south Pole.

antiscab
Senior Member
Posts: 2323
Joined: Mon, 26 Nov 2007, 05:39
Real Name: Matthew Lacey
Location: Perth, WA

mattW's Electric motorcycle conversion Blog

Post by antiscab » Thu, 06 Nov 2008, 05:12

he probably has exams....poor guy....
i do to....its amazing the lengths you feel like going when ur procrastinating :p

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

Rodney
Noobie
Posts: 18
Joined: Tue, 15 Jul 2008, 04:55
Real Name: Rodney O'Donohoe
Location: Adelaide, SA

mattW's Electric motorcycle conversion Blog

Post by Rodney » Fri, 07 Nov 2008, 05:17

Hi,
I hope you didn't think I was trashing your idea, as I was previously going down a similar path. Being an Electronic design engineer with a Power Electronics background, I was just offering some free advice based on my experience. I did have a project to convert a brand new SACHS 150 Express. However after carrying out testing of the unconverted bike I purchased, designing the conversion, and simulating the performance, I decided to cancel the project. (It was disappointing, but the most important skill of a project manager is to know when to change course before you spend too much of your budget).

With the same battery capacity a small car would travel further at highway speeds, due to the lower overal drag. It was as simple as that. Around town at 60Kph the bike could travel further due to lower rolling resistance, and less mass to accelerate.

As for the conversion cost comparison, I was talking about a vehicle that was able to travel continously at highway speeds, (and I was not including the cost of the donor vehicle). Bikes always have a power to weight advantage, (my Aprilia 500 leaves cars for dead), however my Diesel hatchback does over 200kph. Bikes require smaller, lighter weight and hence more expensive components, where a car can get away with more conventional designs. Thundersky cells are less than half the price of A123 cells, but have less than half the Power to Weight ratio, (due to a variety of factors including internal resistance). Rare earth PM DC motors are much more expensive than equivalent Series/Shunt designs. Of course if you are going to have airconditioning, power steering pumps, etc. That adds some cost. But with the same energy needs (battery) and the same continous power (motor/controller) it can be done for the same cost, (albeit a slower accelerating but faster vehicle).

I also owned an electric scooter which was good for around 65kph, and was effectively silent. Occassionally people would step out in front of me, as they could not hear it. Since I have bought the single cyclinder 500cc bike, pedestrians and cars can hear me, even if they can't see me. This has saved me from the "blind lane changers in cages" (car drivers) a couple of times already. This was another major reason can cancelling my motorbike conversion.

I think a 200kph electric bike would not be as good to ride as a 120Kph bike, due to the extra weight and bulk, longer wheelbase etc. That's why most riders tend to move back to more nimble 600cc bikes once they have matured. Thats my 2 cent worth.

Ride Safe o--\o

Rodney.

User avatar
Richo
Senior Member
Posts: 3536
Joined: Mon, 16 Jun 2008, 00:19
Real Name: Richard
Location: Perth, WA

mattW's Electric motorcycle conversion Blog

Post by Richo » Fri, 07 Nov 2008, 21:04

Everyone is entitled to thier opionion I didn't think you were trashing anything.

Your assesment of the drag of a bike vs car appears to be wrong.
The power requirement is also a function of frontal area.
A cars frontal area is much bigger than a motorbike.
SO at the same speed a car will consume about 3x as much as a motorbike.

Bikes can easily do 200kph.
The wheel base does not require lengthening.
Nor a spoiler.
So an electric bike should be no different.
A good bike conversion should be around the same weight.
Obviously if you use lead-acid then it will be heavier.
Help prevent road rage - get outta my way! Blasphemy is a swear word. Magnetic North is a south Pole.

antiscab
Senior Member
Posts: 2323
Joined: Mon, 26 Nov 2007, 05:39
Real Name: Matthew Lacey
Location: Perth, WA

mattW's Electric motorcycle conversion Blog

Post by antiscab » Fri, 07 Nov 2008, 22:15

Hi Rodney,

no worries, you sound like me...just much further ahead.
i dont midn people pointing out flaws in my thinking (of which little details cause me the most grief)...im a big picture kinda guy :)
im still on my scooter. The thundersky batteries i use now are only good for about 6kw, maybe 8 or 9 when theyre warm, in summer ill bump up the controller power again :D.
for a scooter, i can live with that, gets me to 60 pronto, and to 70 eventually (because i hit the pack voltage limit, so power developed has fallen to 1-2kw by this stage).

i still disagree that a car could use less power/energy than a bike at the same speed.
in your comparison your bike uses 4.5L/100km of petrol, and your car uses 5.5L/100km of diesel (which is 30% more energy dense than petrol).
the massive increase in wind resistance is felt equally by both car and bike.
a bike may have a drag coefficient of 1, and a car of 0.35, but the car has way more frontal area, depending of course on what car and bike you're comparing.

even a honda insight needs 7.5kw just to push the air out of the way at 100.

a few mates have mentioned to me 600cc bikes are more fun in traffic....hmm....sounds like a lack of experience on my part there.

cheers,
Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

antiscab
Senior Member
Posts: 2323
Joined: Mon, 26 Nov 2007, 05:39
Real Name: Matthew Lacey
Location: Perth, WA

mattW's Electric motorcycle conversion Blog

Post by antiscab » Fri, 07 Nov 2008, 22:25

i cant say i had thought of using any DC motor on a bike conversion.
I wanted another test platform.

my scooter is getting to the end of what can realistically be done.
i wanted to test out some really high power batteries.
i also wanted to build a 3-phase controller.

but lots of other projects to do first.

out of curiosity, how did you calculate the drag on your bike?
its easy to get hold of the car specifications, not so easy for bikes.

FYI, reason i picked a honda insight for comparison is because it actually does get 4.5L/100km (of course it does a few sneaky things to do that such as lean burn which skews the energy usage comparison somewaht), and can be grey imported from japan reasonably cheaply....

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

Rodney
Noobie
Posts: 18
Joined: Tue, 15 Jul 2008, 04:55
Real Name: Rodney O'Donohoe
Location: Adelaide, SA

mattW's Electric motorcycle conversion Blog

Post by Rodney » Sat, 08 Nov 2008, 05:42

Well it appears that my comments have at least got this blog going again.

Regarding the issue of Aerodynamic drag and Cars vs Bikes:
The formulae is
Fd=0.5*ρ u^2 Cd A
where
Fd is the force of drag (Newtons).
ρ is the mass density of the fluid (air in our case).
u is the velocity of the object relative to the fluid (m/s).
A is the reference area (m^2).
Cd is the drag coefficient — a dimensionless constant, e.g. 0.25 to 0.45 for a car. Most modern cars are around 0.3

What is important is the CdA value, that is Cd * Area.
Whilst the effective Area of a small car is about 3 times greater than a motorcycle and its rider, the Drag coefficient is much less around 0.3 for a good car compared with 1 to 1.1 for a motorcycle. So a small car like a Toyota Yaris Sedan, or a Mazda 2, etc. can have a lower CdA value than a Motorcycle and its rider. Sports bikes go faster largely because of the more aerodynamic (and uncomfortable) riding position which both lowers the frontal area and Cd.

When traveling at 50 to 60 kph in metro traffic, the motorbike wins the energy battle due to its lower mass that needs to be accelerated (less Kinetic energy lost during every start-stop cycle), combined with a lower rolling resistance. However at highway speeds, much more energy is required to overcome the Aerodynamic drag (about 4 times as much).

As Matt correctly pointed out Diesel engines get more energy out of the fuel per litre, than petrol engines. The figures I gave were my normal around town driving/riding. Perhaps a better comparison should have been my Toyota Yaris sedan (1150 Kg with 100Kg driver) that I owned before which achieved around 7 L/100K around town compared to the 500cc bikes 4.5 L/100Km both running on standard unleaded. However on the highway the yaris achieved 4.5L/100Km at 110Kph (aircond on), and the bike uses about 5 L/100Km (at 100kph). So as I said, bikes use less energy in city traffic, cars are better on highways.

The Honda Insight 7.5Kw at 100kph is much better than my SACHS 150 Express donor bike, which had 8.8Kw but struggled to exceed 90kph (speedo reads 100).

My little electric scooter did a great job in the metro area, which inspired me to build something faster. Can be done, but a car is more comfortable at higher speeds, and uses less energy. Hence my choice.

Regarding how to calculate the drag:
The most pragmatic answer is there is no need to. What is needed is to calculate the total force required to propel the vehicle on a flat road at various speeds. That is, the total of Aerodynamic drag and Rolling resistance. There are a few ways of doing this, however my preferred method is to accelerate the vehicle to 10kph above your maximum intended speed (legally of course), get someone else to start recording the speed vs time (a camcorder is a great way), then disengage the clutch (but leave the vehicle in gear to account for transmission losses) and allow the vehicle to slow down.

To determine the drag at 100kph you note the time taken to slow from 105 to 95kph. Then divide by 10 to get Kph/second deceleration. Then divide by 3.6 to get m/s/s deceleration. Then multiply by the total vehicle mass in Kg (including everyone in the car). This will then give you the force required in Newtons. If you want to know the power required (in Watts at the wheels) then multiply the force (Newtons) by the speed in metres/second (kph divided by 3.6).

Regarding the choice of a DC motor
Well I am not a fan of most Series wound or Shunt wound DC motors used in conversions due to their relatively low efficiency, particularly under heavy or light loads. If you can operate in the efficiency sweet spot (85%) they are not too bad. (You can tell a lot about a product by what is left out of the data sheets). Their low efficiency is mainly due to the energy wasted to produce the "static" magnetic field (usually in the stator). Series wound motors have Magnetic saturation under heavy load, and too weak a field under light load. Shunt wound motors are better but still waste power in the field (shunt) winding. However PM (Permanent Magnet) motors are a different story.

PM motors like PERM-132, E-tek, etc use very strong (high flux) permanent magnets to create a stator magnetic field, and hence don't waste energy like series/shunt wound motors. The modern bus-bar designs also have much lower winding resistance which provides good effeciency (90%) over the very flat speed torque curve, so that speed won't change much under load. This is both a blessing and a curse. Unlike a series wound motor, a PM motor must have a current limited speed controller with high peak current capability (a PERM132 has a 1440A locked rotor current at just 24V, (4320A at 72V) which is a lot for a 7.2KW motor).

Series wound motors were designed to work with simple resistor start / voltage switching circuits as found in old trams, forklifts, etc. Where the motor will build up speed gradually with a fixed voltage, but will slow down a lot under load (a bit like steam engines). Good simple technology for those applications.

A word of warning, if your DC controller fails short circuit, then the modern PM DC motor will break something when it reaches locked rotor torque eg. Hopefully your motor fuse, a chain, tyre traction, your spine (when the bike flips back). Battery resistance may even save the day. A series wound motor would treat you much more kindly (maybe not if your on two wheels). Keep the main isolator switch very handy.

My design was to aim for a 90kph top speed at 80% discharge of the battery. This was the speed limit on most highways within Adelaide Metro Area (was 110kph in the old days). It allowed the motor to run at its rated continous power (7.2KW). Provided good acceleration with 450Amp (85 Nm at PERM motor) about 18 kph/second. And should have delivered a 120km range at 60kph with a 72V 90AH TS battery pack (72 kg). A reasonable compromise all round for a cost of about $9k before the dollar went for a dive.

I am waiting for a mass produced electric car, the Mitsubishi MiEV is due to arrive late 2009/early 2010. The trouble with building a new EV is you buy a new car, throw out the most expensive bit (engine), and pay spare parts prices to replace those expensive bits with an electric drive train. In the appliance business a 100W electric motor may sell for $140 as a spare, but only costs the factory $7. EVs should be cheaper than petrol cars once the volumes get up there.

In the mean time converting a "classic sports" car makes quite a lot of sense, especially with an optional V8 engine noise simulator. I'd love and Electric Mustang.

But my engineering interest is now with how fast you can go with a full aerofoil (Cd=0.04) fairing on a 200W electric-pedal hybrid recumbent bicycle. (No Rego costs, can use bicycle lanes, and keeps you dry when it rains to). The pedal only record is 81Mph (130Kph), so doing 90kph (1/3 the power) with electric assist should be achievable for normal people.

Rodney :-)
Current EVs:

Mitsubishi i MiEV MY12.

User avatar
Electrocycle
Senior Member
Posts: 985
Joined: Sun, 19 Oct 2008, 20:23
Real Name: Andrew
Location: Sydney
MSN: dumhed@dumhed.com
Contact:

mattW's Electric motorcycle conversion Blog

Post by Electrocycle » Sat, 08 Nov 2008, 19:38

that'd be a scary thing to ride!

Motorcycles are definitely not aerodynamically efficient, but I also don't think they're generally being converted primarily for highway use.
Actually, electric power in general is a bit pointless for highway use - where IC engines are at their most efficient, and long range is most important.

Back to the aero, I had a 250cc sports bike, which did 0-100 in about 5.5 seconds. My car did 0-100 in about 7.5 seconds. The car was *much* quicker at getting to 140 than the bike though!
You can really feel an aerodynamic brick wall above about 80 on a bike.

So, even though a bike will need more power than a car to maintain highway cruising speeds on flat ground, it needs a lot less power to perform acceptably for "round town" transport, to climb hills, etc.

Imagine a bike and a car with the same motor and batteries.
In theory the car will go further on the highway, but you can bet its performance in traffic will be dismal, and as soon as you point it up a hill it's basically going to come to a stop!

When a started looking at doing an electric conversion, the first step was to decide how it would be used.
I wanted something to run to and from the train station, local shops, etc. A bike is much easier to store, park, engineer, and register - and you can get reasonable performance out of much smaller motors and batteries.
My bike as is performs fine for its intended purpose, but to achieve the same sort of results in even a small car would require at least 4 times the power and battery capacity.
The Engine Whisperer - fixer of things

Post Reply