Electric Motorcycles

So far I'm thinking:

• Electric motor with 10-20hp peak and maybe 1-2hp continuous.
• Simple chain drive to rear wheel.
• About 80kg of sealed batteries in case it falls over -- maybe Optima Yellow Top? Either a 48V or a 60V system.
• Some kind of twistgrip controller. Are regenerative ones available in this power range?
• Some kind of onboard charger, so the bike can just be plugged in to the 240V mains and left overnight / at work / etc.
• All shoehorned into a rolling chassis from a streamlined 250-400cc commuter would be about right ... kerb weight about 160kg before, less than 200kg after I hope.

Does this sound reasonable?

I've gone through the bikes in the photo album and going by the stated ranges and battery configs, the efficiency seems to vary enormously ... between 50 Wh/km and 400 Wh/km! Anyone know a good rule of thumb for a two-wheeled electric beastie?

I'd need to get a 'regular' range of maybe 40km (25mi) and a 'regular' speed of 60km/h (38mi/h) out of it to make it a practical bike, and maybe occasionally a 60km (38 mi) range or a 80km/h (50 mi/h) top speed.

Is this practical with the available tech, or will I just have to wait for fuel cells or unobtainium batteries or something?

Thanks!

-----Nick 'sharks' Moore

Some investigation

Wh/km

Battery			Range	Speed	Drain	Name	Batteries	Motor	Final Drive
V	Ah	Wh	km	kmh	Wh/km				Type	Ratio
48	22	1056	51-64	64	29	Jackal	SLA	ETek	Chain
48	65	3120	32-51	77	76	EMB Lectra	Optima D750S	Etek	Chain	3.375
48	55	2460	48	80	55	E-Scramler	PowerSonic 55Ah	Advanced DC	Chain	2.53
48	40	1920	40	81	48	250XL	SLA 40Ah	Etek	Chain
48	50	2400	30	86	80	Xineta	Hawker 12V 50Ah	Cupex (perm)	Chain
48	44	2112	24-40	88	66	ReCycle	22AH SLA (paired)	Etek	Chain
36	115	4140	32	88	129	ElectroCycle	trojan 12V TMH	Prestolite	Chain	6
72	41	2952	6-13	100+	307	BEM	Optima YT D51	Advanced DC	Chain
60	55	3300	32-40	100	91	ElectricNinja	55AH	Etek	Chain
72	100	7200	27	104	265	Piggy	Trojan 100AH	Advanced DC	Chain	4.6
96	42	4032	24-32	128+	144	REVision	Hawker Genesis	Advanced DC	Shaft	~3

Of course, this is total battery Wh, not actual Wh used to travel that range. There's a huge variation in claimed efficiency though ... perhaps different depth-of-discharge (DoD) strategies, different motors, different gearing, aerodynamics all add up.

Choosing Batteries / Optimizing Optimas

I'll probably be stuck with the lower lines on the graph, eg: Optima YTs or Federal Gel-Tech, because the deep-cycle types don't offer enough peak amps. Such is the way of engineering tradeoffs!	Found some good numbers of Optima YTs discharge cycle, and it seems like about 40% DoD should give the best lifetime in km.

Practicalities

So for a ~35km range I'd need 3.5kWh off battery capacity ...

#	Type	Capacity (total)					Weight (total)	Size (each)	Price Retail (total)	Value
		V	Ah(20hr)	Wh(cap)	CCA	Peak kW	kg	mm	AUD	Wh / $
4	Optima YT D31	48	75	3600	900	43.2	108	325*165*238	$1840	1.9
4	Federal Gel-Tech 8G24	48	73.6	3530	410	19.7	97	276*171*251	$1200	2.9
5	Optima YT D34	60	55	3300	750	45.0	97.5	254*178*198	$1925	1.7
6	Federal Gel-Tech 8G22NF	72	50	3600	245	17.6	103	238*140*235	$1434	2.5
14	Thunder Sky LiIon TS-LMP80	50.4	80	4032	?200?	?10?	42	220*145*61	?$2000?	?2?
14	Thunder Sky LiIon TS-LMP200	50.4	200	10080	?200?	?10?	95.2	285*182*100	?$5000?	?2?

... fitting them into a bike-sized vehicle won't be easy. Cardboard models seem the way to go. I've added in LiIon battery options because they might be a good option ... they seem to be about the same $/Wh but half the kg/Wh. On the down-side, they require a per-cell Battery Management System. See Victor's CRX under 'Links:' below ...

Motor and Drivetrain

The simplest setup is likely to be the permanent-magnet Etek M7 from Briggs & Stratton. They're pretty widely used in the electric motorcycle world. There's quite a bit of info on the Etek at robotcombat.com and powerped.com.au (scroll down) and it looks like it'd be easy enough to mount in a motorcycle application.

The Etek will spin at 72RPM/volt, so at 48V that's a top speed of 3456RPM. A motorcycle wheel&tyre is about (hand wave) 2m in circumference. Front sprockets go down to about 13 teeth, and rears up to about 57, so we'd have a max speed of 3456 RPM * 13/57 * 2 m/R = 26 m/s, or about 94 kmh flat chat. Sounds about right, perhaps a little high, but to get a higher final drive ratio would mean adding an idler shaft or similar, and I'd rather not. On the other hand, if you were going to add an idler shaft, you could add it coaxial to the swingarm pivot, to keep the chain/belt lengths constant.

Motorcycle sprockets are generally splined to fit a shaft, but it's probably easier to machine a sleeve keyed on the inside to fit the Etek output shaft and stepped on the outside to make it easy to braze/weld the front sprocket to the sleeve.

Regeneration!

One of the disappointing things about a permanent magnet setup is that it makes it hard to do regenerative braking. Since motor voltage is proportional to motor RPM, the only time you'll get a voltage high enough to recharge the batteries is revving the motor beyond its normal maximum RPM ... and on a direct-drive machine, that'd only be when rolling down a hill quicker than the bikes top speed ... not likely to be a common occurance ... One way around this is to use a "Contactor controller", or series-parallel switch. Put simply: split the pack in half, and wire these halves up so that they can be connected in series or parallel. This provides two 'gears' ... in parallel, maximum current is increased for more torque, and in series maximum voltage is increased for more top speed. Pretty obviously, fuses would be needed to prevent the batteries exploding if a contactor stuck or was closed at the wrong time. And, of course, dropping down into Parallel reduces the battery voltage, so if you've sped up to top speed in Series and then shift into Parallel, there's sufficient voltage to regeneratively charge the batteries. It's not exactly sophisticated, but it's a start. The idea can be extended: Num Batteries Num Gears. Gears ( Nseries * Nparallel ) Top Speeds With top gear top speed = 100 2 2 1 * 2 2 * 1 50 100 4 3 1 * 4 2 * 2 4 * 1 25 50 100 6 4 1 * 6 2 * 3 3 * 2 6 * 1 17 33 50 100 8 4 1 * 8 2 * 4 4 * 2 8 * 1 12 25 50 100 The complexity gets out of hand pretty rapidly. Six is probably the largest useful number ... Just as the selection of series vs. parallel is a bit like the selection of gears in a gearbox, the two likely strategies are manual or automatic switching. For manual switching, a control would select which contactors to close, giving a selection "Parallel-Neutral-Series" just like 1-N-2 on a motorcycle gearbox. The throttle setting would provide PWM control over power and regen. For automatic switching, a controller would monitor throttle position, battery voltage and motor voltage, and select the appropriate 'gear' and PWM setting. Someone on the list pointed out that this would be a Bad Idea with most controllers: the input stage capactitors need 'precharging', generally done by a resistor in parallel with the contactor. Switching voltages would be messy. Instead, if you wanted to do S/P switching, you'd need a controller designed for the job, with input stage capacitors _before_ the switch. Since the S/P switching is mostly there to do regeneration, and since the controllers people are talking about don't do regen anyway, it's not a big deal -- I'd need to build my own controller anyway! Old Shopping List Kawasaki GPX250 or similar rolling chassis inc. minor repairs trading post? $500 Chain & Sprockets (motorcycle) bike shop $250 KIT: Etek M7, Alltrax controller, charger, throttle currietech.com.au $2400 4 * Optima YT D31 ? $2000 Motor mount plate & front sprocket carrier & battery cages custom $300 Sundries: (lights, paint, shrinkage)   $500 TOTAL: $5950 ... which, sadly, probably puts this project out of my league. Compared to buying a decent GPX250 for $3000 and $3000 worth of fuel, it'd take perhaps 40,000km to break even ... and given the range (40km or so), that's 1000 discharge/recharge cycles (perhaps 3 years) and by then the batteries are probably half shagged. Oh well. It'd be a nice toy :-). New Shopping List On the other hand, if the batteries and controller could be gotten cheaper, perhaps by sponsorship on the batteries and by importing parts directly from the States (I've seen Etek+controller for US$700), perhaps it'd break even ... perhaps this explains why most of the E-vehicles seem to be from the States, even though fuel is cheap over there. The constant torque of a DC motor, as compared to the jerkiness of a ICE, probably means I could get away with a light chain. Belt drive is another option, but finding matching ratios may be a problem. Actually Cloud Electric have #40 sprockets down to 11 tooth (on a 7/8" shaft) and up to 60 teeth on a four-hole rear sprocket. So ratios up to about 5.5:1 might be possible. Kawasaki GPX250 or similar rolling chassis inc. minor repairs trading post? $ 500 Chain & Sprockets (#40) Cloud Electric $ 100 KIT: Etek M7, Alltrax 300A, etc Cloud Electric $1200 4 * Gel-Tech 8G24 Solar Online $1200 2 * 24V 6A Smart Chargers Jaycar $ 200 Motor mount plate & battery cages custom $ 200 Sundries: (rattlecan paint)   $ 100 TOTAL: $3500 ... which makes it look a lot more tempting ... hmmmm ... LiIon Batteries The limiting factor on the above is the sheer weight of batteries it'd need to lug around, so I'm considering what could be done with LiIons. Thunder Sky have Lithium cells at prices competitive with a Optima YT pack. Apparently they're Cr-F-Li chemistry. TS-LCP50AHA 3.6V 50Ah 1600g 190x116x46 US$98. TC-LCP100AHA 3.6V 100Ah 3000g 220x145x61 US$200. To get to a nominal 48V (for the Etek) it'd need about 14 cells in series: so that'd be 42kg / US$2800 for the 100Ah pack. One limitation of these cells is that they become quite inefficent past 2CA discharge, eg: you shouldn't try to get more than 100A out of a 50Ah cell. This makes a series/parallel setup essential to run an Etek motor ... with two banks in parallel, you could source 200A without sagging much. Another possibility is to use UltraCapacitors as an intermediary. The other problem is that LiIon batteries need a per-cell Battery Management System. Mostly what this seems to be is a method for making sure that the voltage across a 3.6V nominal cell never gets above about 4.3V. The easiest way to do this is to shunt current past the cell, with a circuit which is more-or-less a 'sharper' version of a Zener diode. Simple charging system: A power supply capable of 32V 10A sits across a bank of 7 Lithium cells, each of which is clamped to 4.3V. While they're charging, the bank voltage will be <30V. When all shunts are shunting, bank voltage will have risen to 30.1V, at which point the charger can turn itself off. These batteries apparently like to be variable current charged, so the one power supply can switch once a minute between the two banks. Now, admittedly, that's a 320VA PSU we're talking about, so it's still no lightweight. But it's not a welder either, and it doesn't have to be too sophisticated since the clampers do almost all the regulation. They also have integrated packs with built-in charger at very good prices. Two of the 24V packs seem the obvious easy solution to my e-bike's power needs, but I'd like something which could handle regeneration ... TS-IC36V18AH 36V 18Ah 7200g 415x97x132 US$300. TS-IC24V50AH 24V 50Ah 18kg 405x122x202 US$700. TS-IC24V90AH 24V 90Ah 24kg 490x120x217 US$1000. ... still, it might be an effective way to get started without building too much fancy stuff. Two 24V 90Ah packs, a series/parallel contactor setup on a 'gear shift' (no clutch, so left hand has some free time) and it'd be away! About the same price as 4*Optimas + 2*chargers, slightly better range and half the weight. Sounds like a pretty good deal. It'd mean I could move to a lighter chassis, too -- now, a Gilera CX125, that'd be cool! Pity they're a little on the rare side. LiIon Shopping List: Light motorcycle rolling chassis inc. minor repairs trading post? $ 500 Chain & Sprockets (#40) Cloud Electric $ 100 KIT: Etek M7, Alltrax 300A, etc Cloud Electric $1200 2 * TS-IC24V90AH 24V 90Ah batteries w/ inbuilt charger ThunderSky $2666 Motor mount plate & battery cages custom $ 200 Sundries: (rattlecan paint)   $ 100 TOTAL: $4766 Links Stuff: Two crazy hybrid motorcycle ideas I had Electric skateboard idea Other People's EVs: Victor Tikhonov's AC Honda Lots of photos and notes on an Siemens AC / LiIon / Ultra-capacitor driven electric car. Serious Stuff. Electric Motorcycles Photo Album Electric-bikes.com UBC Electric Bike Club EV Mailing List(s): Instructions for joining the EV List EV List Archives The EV Tech mailing list Power-Assist Yahoogroup (for power-assisted bicycles, mostly). Australian Suppliers: DLM Energy sell e-bike parts EVS aka Currietech (St. Kilda) Sell ETEK M7 motor and controller Solar Online have Federal Gel-Tech batteries cheap Rainbow Power Company have various solar power bits and pieces. International Suppliers: Cloud Electric (USA) Brilliant range of E-stuff. EV America (USA) Golden Motor: hub motors (China) Electric Motor Sport (USA) Thunder Sky LiIon batteries (China) High-tech doodads: IXYS Semiconductors: high-current MOSFETS International Rectifier who have a lot of technical papers on semiconductors on their site.