# Plywood, Fiberglass, Epoxy Electric Moped plan



## JohninCR (May 6, 2008)

Here in Costa Rica, EVs fall thru the cracks in the law. If it can be pedaled, and doesn't have a gas engine > 49cc, it's a bicycle. ie No annual taxes, inspection, registration, license, helmet, etc. These are significant costs and pains in the butt down here.

I'm working on an extremely lightweight catamaran right now of very thin plywood, fiberglass, and epoxy construction, and since a bike has even less sideways forces, I believe I can use the same easy construction method for building a powerful moped. I'll probably want to include some carbon fiber in the composite near the high stress points.

Below is what I have in mind. The metal motor mount and drivetrain will be housed in the wider section between the swing arm assembly, and the batteries and electronics will be housed in the body. I believe that cheaply and easily I can construct a comfortable lightweight cruiser with a low center of gravity that has plenty of room for batteries.

Here's a crude drawing and a pic of the 6in dia x 12.5"long 36V motor I plan to use (approx 30lbs) along with a Comet torque converter between the motor and chain.

http://www.firstlines.net/ElectricChopper.JPG
http://www.firstlines.net/ChopperMotor.JPG

John


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## mattW (Sep 14, 2007)

Sounds pretty ambitious, but I can't see any reason why it wouldn't work. What sort of performance specs are you hoping for?


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## JohninCR (May 6, 2008)

I don't really have any performance goals yet. Supposedly the motor was designed for a scooter to take 2 people to 50mph. My goal is more torque and take-off than speed, but only to be far more efficient than a car in traffic. I've gotten to where I don't want to leave my home/office in the afternoons due to traffic, and here weaving to the front by any means is ok, as traffic laws are only to establish fault in an accident instead of enforced rules. 

It's just for fun and local errands, so range isn't really a consideration. We'll see how it does with a reasonable weight in lead acids, before investing and waiting for better batteries, which shouldn't be too far down the pipe. The bottom line is that with this much stronger motor, and maybe 50-60lbs more weight than my electric bike not considering batteries, I should have something fun, not an ice wagon.

Matt, you said ambitious, but where are the pitfalls? I plan to stick to smooth asphalt roads, so I don't need a lot of travel in my suspension. I'll build my center console to fit more batteries than I've seen on most bikes (6-8 full size 12V deep cycle), while keeping them lower to the ground than a normal motorcycle frame would allow. Plus I'll likely overbuild the high stress connections, but still have something fairly lightweight. I already have the motor along with a Kelly 200/100A 24-36v controller, as well as a Curtis 1205-205 that is good for a peak of 350A and 36-48V. I believe the torque converter will not only help with takeoff and hill climbing, but it should also give me more flexibility and reduce the stress on the drive train.

I'll also soon have a donor bike without a motor to use as a test bed, and to get a better idea of gearing ratios and battery requirements before dimensioning my lightweight build, not to mention rob the electronics for lights, turn signals, etc.

All advice or opinions is greatly appreciated.

John


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## JRP3 (Mar 7, 2008)

If you're comfortable with epoxy and fiberglass cloth you might want to consider using insulating foam board as a core material instead of wood. It's easy to shape, lightweight, and very strong. I've seen instructions for building a recombinant bike using that method. 
I thought this was for free somewhere on the net:
http://www.rqriley.com/xr2.htm
A different setup:
http://www.instructables.com/id/SGFEQ1NFAQEDGF9/


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## JohninCR (May 6, 2008)

JRP,

Something I didn't mention is that I like to do things the easy and fast way. If I was building a bicycle then I'd go one of those routes. Instead of a frame as a skeleton to support an exterior skin, I plan to obtain strength more like an insect does with a strong skin that supports the interior guts. Using a foam core board could achieve a similar result, but for only slightly more work to cut the 3-4mm ply, I think I can achieve a narrower form that is ultimately stronger. Also, I'm far more comfortable working with wood, even if it is only the base material.

With some slight bending of the plywood, then it becomes "tortured plywood" which spreads the load over the entire panel instead of locally. Hopefully the end result will be a structure that has a bit of "give" but with similar overall strength to a carbon frame, resulting in a better ride quality than a carbon frame without the cost and extra work, at no more than a few pounds of weight penalty.

Even if I went with a carbon frame to ultimately save weight, then I'd still have to create an exterior shell. Not only do I question my finishing skills going that route, but I question whether I can create the same overall strength to weight ratio. Insects are a lot tougher and stronger than we are.

Also, I'm already planning another larger boat for which I will negotiate directly with a plywood manufacturer locally, so I may be able to get an exotic wood veneer on some sheets to use for my super moped and go with a totally clear finish. I think a "green" electric "woody" chopper moped has the potential for making me a proud papa of something my kids and future grandkids could appreciate and enjoy. Carbon, metal, and other composite vehicles are a dime a dozen compared to what I have in mind. Just look at some of the artwork the experts are able to pull off with kayaks of wood/epoxy/fiberglass construction. Even if I can't pull off a wooden piece of art, I can always paint it as a last resort, so wish me luck.

John


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## JRP3 (Mar 7, 2008)

I agree a wood finished EV would be neat. One last point for foam though, foam boards can be bent and stressed just as plywood and used as an outer skin, and you could glue a wood veneer to the outside of the foam as well. Good luck either way.


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## JohninCR (May 6, 2008)

Is there a benefit to foam that I'm missing? Sure it would be easier to cut and shape, but it wouldn't seem to add anything to the structural strength. Just the epoxy impregnated ply alone will almost support the battery weight. I'd think 1/2" would be about as thin as you'd want to start with for foam, so that's 1" in width + the minimum width the batteries need before any composite layers. 

4mm ply on the other hand nets me only 1/3" of width, and impregnated in tortured form gives me quite a bit of strength and rigidity before the fiberglassing. Also with vacuum bagging I get very close to a fine finish from the start. I haven't worked with composite layers and foam, but without a mold, it seems like the sanding process is a lot of work. That's why I'm going with this method for a boat. In a week my son and I can knock out the hulls for a 30ft catamaran with the end result being arguably stronger hulls with very little additional weight compared to the lightest composite construction.

Check out Kurt Hughes method at http://www.multihulldesigns.com/pdf/cm33.pdf

John


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## JRP3 (Mar 7, 2008)

For a given thickness plywood is actually pretty heavy. The foam would save you a good amount of weight, there is a reason why high end composite boat builders use foam core instead of plywood. 1/2" foam weighs less than 1/4" plywood. The plywood method probably would be faster for you though. I'm sure a good product could be made either way, but vacuum bagged foam core will be lighter, and of course can't rot if water somehow enters the core.


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## JohninCR (May 6, 2008)

Thanks for the input JRP,
Just making sure I'm not missing something. BTW, this ply is more like 1/8th. I'm a big guy, so any weight differential is less than my weight fluctuates over a day or two period anyway. Quick, easy and in my construction comfort zone makes for a better project for me. Plus I can likely pull off something more unique if things are neat and tidy enough to stay with a clear coat, maybe even a solid exotic wood instrument console for the top access panel which would be the gas tank location on a gasoline bike.
John


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## JohninCR (May 6, 2008)

BTW, How much ventilation should I factor in for my battery and controller compartment? Should it be the same for lead vs lithium? Since each stage has a given efficiency of less than 100%, can I calculate fairly accurately how much heat I need to dissipate? I'll treat the drive train section separately with plenty of ventilation, and the motor is sealed with that nice heat sink, so my concern there is more about keeping out the road grime and/or making it easy to clean.

John


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## JRP3 (Mar 7, 2008)

The controller might need to dissipate a fair amount of heat so make sure it gets good air flow. I don't know about the batteries.


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