........................................CRANK MONSTER II . . . Balsa Wood Bike Frame
The original Crank Monster aluminium frame is showing some wear and producing a few rattles as well as a stress crack showing on the bottom near the steering tube.
Its time for a new frame. Since I don't have a worthwhile alloy frame kicking around its time to play with a composite frame. This one will be made of a few materials on a very restricted budget.
Materials will be 4 ounce dense styrofoam core. Aluminium parts will be bonded to the core using automotive panel epoxy. Bottom bracket, steering tube and seat tube will be stolen off a cheap aluminium frame and epoxyed to the core then fibreglass wrapped. The main stress points will use carbon fibre uni-directional fibres 2" tape or similar on top of the fibreglass in as many layers as needed probably 4 layers on top of 4 fibreglass. Fibreglass is being used as a base with minimal carbon fibre simply due to costs. Using all carbon fibre would triple the cost. (see note at bottom about carbon fibre recycling) Epoxy resin will be used instead of fibreglass resin for the added strength. I was aiming for 1300 to 1500 grams for the frame but with extra fibreglass and balsa needed to be strong enough it will likely end up around 1500 to 1800 grams. Rear tire clearance is accounted for as well since I ride wide knobbies in the winter and summer slicks.
The frame style is closer to a road bike or track bike but it is designed for a mountain bike. It has the same dimensions and geometry as the aluminium frame. I used a plumb-bob and a 360 degree protractor to find all angles. Second pic shows drawing used as a base for designing that has the same critical measurements and geometry as the original Crank Monster frame. Front derailleur mounting boss might be eliminated and go with just the gears on the back. Designing a frame of this type makes including suspension much more difficult. It would be very hard to make suspension mounting points strong enough to handle the forces in a suspension. The pivots and mounting points are what are causing the noise now so I want to eliminate those problems and weight. I will be using the Suntour front suspension fork that is on the Crank Monster now. The frame jig and foam core will be done over the winter and the finished frame ready for spring 2011.
While visiting my favourite model and r/c hobby shop I stopped to check out the balsa wood for another project. I picked up a 1x1x36" piece and found there was very little flex to it. I know it handled being bent much better than a hunk of 4 ounce dense styrofoam would be able to handle. It is very strong in comparison with styrofoam (probably as much as 100 times ) and not much difference in weight. Therefore I may pursue using balsa instead or a combination of styrofoam and balsa using balsa as the core. Balsa is as easy to work as foam even using the same tools. It would be a few grams more weight than a foam core but many times stronger. I think 4 pieces of 1x1 laminated into a 1x4 with epoxy for the main beam then covered in foam and shaped then fibreglass etc in the frame shape of the drawing. Two triangulated 1x1/2 will go in the rear stays, one to the bottom of the seat tube and one to the bottom bracket as the core. Additional 1x1 balsa maybe added for the high stress areas as gussets. The same 4 ounce dense Styrofoam will be used to fill in the blank spaces and a 1/2" sheet over the balsa then shaped to frame dimensions.
Balsa may seem an unusual material to use but balsa is used in some small 2 and 4 passenger planes and avionics in numerous areas and in the floorpan of the Corvette Z06 sandwiched between fibreglass. Its more than just a model makers material. Its showing up as the core for many types of composites because of its strength and weight.
The layout of the balsa I was able to get. 2 - 3 x 1/2 laminated with 2 - 1 x 1/2 to fill in to make up the 1 x 4 needed.
Note: this design is ongoing and drawings will likely change often.
I'm finally kicking this frame project back into action. I started gathering materials. A small design change to the balsa layout since 1x1 wasn't available so I ended up with 1/2 x 3 which will be laminated the same way with the main beam of two 1/2 x 3 to give the same dimensions. An inch will have to be added in to make the four inch beam of the design. Maybe overlap the 1/2 x 3 by 1 inch and laminate in 1 inch pieces to produce the needed 1 x 4. The rear stay will get a 1/2 x 3 for the bottom bar so only a small 1/2 x 1 will be needed for the top brace.GEARS
Well the Crank Monster II is coming along more in the design. I have committed to changing the whole drive train. Out with the open gears and derailleurs and in with an internal hub. After much research the Shimano Nexus Alfine S-GS500 8 speed internal hub is my choice. There will have to be a few changes to the frame design but I think it will be worth it. The Nexus model I got has a coaster brake built in which means back peddling for rear brakes and also that I can eliminate the back brake lever and cable. The frame will not have the brake boss pins so those two parts are gone from my design. This means there will be a cable to the gears most of which will be embedded into the frame and one front brake cable. Front brakes will stay the same.
Gear . . . . . 1 . . . . . . 2 . . . . . . 3 . . . . . . 4 . . . . . 5 . . . . . . 6 . . . . . . . 7 . . . . . 8
Ratio . . . .0.527 . . . 0.644 . . . .0.748 . . . 0.851 . . 1.000 . . . .1.223 . . . . 1.419 . . 1.615
Step . . . . . . . 22.3% . . . .16.0% . . . .13.9% . . .17.5% . . .22.3% . . . 16.0% . . . .13.9%
The only change I will need to make to the frame design is to make some rear lugs that have a horizontal slot so I can adjust chain tension. Or the other option is to use a chain tensioner (more like a non-shifting rear derailleur) and a chain the same length as with a gear cluster. The rear dropouts I planned on using would work good for an open gear and derailleur system but no way to adjust chain length being vertical cutouts. I also have to go to a single gear crank which saves having another derailleur, cable and two more chainrings.
It will be a fair bit more expensive than just replacing the back wheel and gear controls with open gears and derailleur. The Nexus hub with a matching shifter runs about $400 (CDN) then it still needs a rim and spokes plus the cost of a single gear crankset. A rim and spokes will be assembled by my local Bike Shop. I built those sweet wheels on the Crank Monster but I don't want to spend up to 500 to match that quality. The titanium spokes are ridiculous in price these days and a more common brand name rim with stainless steel spokes will be more than enough wheel for my needs. Because of the coaster brake I can use a rim for disc brakes instead of rim clampers so that will make for a cleaner look.
Costs will run about $800 total. Hub 320 and shifter 60, wheel build 200 and a decent single gear crank 100. The last 100 is for frame materials.
Of course I will be using it on the Crank Monster until the new frame is done.
It seems like a pretty expensive gear change but then I did spend 1400 on a $500 bike to create the Crank Monster 7 years ago.
Note : used carbon fibre can be re-cycled by soaking in a solvent of the appropriate type or burned off. The carbon fibres are not affected by baking or low temp burning the resins out of it and most solvents. Once resin is burned and powdery, flex and shake and blow off with air, rinse and dry. I would avoid pieces that are discarded because of cracks since the fibres would be broken. If you put a value to your time it works out not much cheaper than buying new unless it is a large amount. Woven cloth would be the easiest to find. Recycling carbon fibre requires appropriate safety gear such as goggles, mask and thick latex gloves with lots of ventilation preferably outside. The resins produce lots of mildly toxic smoke when burned. The proper way to burn it off would be to use an enclosed oven with a heavily filtered exhaust utilising wet filtration and carbon particle filters. Recommended if doing lots.Frame Build
First layout of parts and balsa. I drew out the angles and dimensions on the plywood first. A few parts need to be trimmed to fit as well as some duplicate parts for other wheel stay and building up to 1" thick. The main beam will fit into the down tube with a tenon joint for added strength. All joints and connections will be with 2 part 5 minute epoxy.
The top and bottom 1x1/2 beams of the rear stays. The 1/8 plywood will add considerable strength to all the joints.
Pen marks show size of plywood insert. Also note alignment marks. To make the cutouts for the plywood I drilled 1/8 holes along the outlline of the plywood plug along the centre line then used a razor knife to cut out. I'm glad its balsa. Oh ya, just for a giggle, the plywood is from a peach box. Parts of it got used in a certain canard wing jet model I did a few years back, shown elsewhere in this forum.
Rear stay showing bracing epoxied in.
Main beam to seat post mortise and tenon joint before epoxy.
Both the rear stays and the mortise and tenon joint turned out to be many times stronger than I expected. I stood both rear stays on edge and did a hand stand on them (I'm 140 lb.) Very strong stays.
Yet another lay-out to check everything. Rear stays will get sunken into the seat post about half the thickness (1/4"). A jig is next to stand up the frame and align everything before attaching the rear stays. Note board between rear stays to keep it at 133 mm apart, same width as a back wheel.
Rear stays showing styrofoam filling in spaces and to sandwich both sides. Inside of stays will be cut back lots but 1" foam was all that was available. Have lots of Olfa knife blades handy.
Note cutouts to allow for aluminum dropout pieces. Any small gaps will be filled with 2 part epoxy adhesive. Any larger gaps elsewhere will get 2 part gel epoxy adhesive which won't drip or droop in thicker applications.
Note slot in main beam for plywood biscuit in angled braces, matching slot on other edge of main beam. Rear stay in background has had foam sliced to a half inch.
Black squares at brace joints are outline of plywood biscuits inside.
Frame with spaces filled in and is a 1" slab. Panel beside goes on top, pen marks show approximate shape although It will be much slimmer looking. Total thickness of the foam once all glued together will be 3", most of which will get cut off. Finished main beam thickness will be no thicker than 1 1/2". Refer to first drawing at top of this post for actual shape.
All the holes I drilled in the aluminum tabs were filled with epoxy after drilling down into balsa 1/8" deep through each hole. This forms a pattern of 1/8" epoxy knobs secured into the wood.
3" styrofoam sandwich. Not glued together yet since I need to fill some cracks and spaces with epoxy first and attach the rear stays.
It would have been better if the outside panels were 1/2" thick instead of 1" so there would be less cutting and carving.
Front part of frame trimmed closer to shape. Now to thin it down to 1 1/2" thick and round out the edges into peaked curves. Rear stays and their extra bracing are next to go on.
Frame in jig after epoxying the rear stays on. It is all lined up along the green line on plywood. Note plumb bob hanging off front. A couple drops of crazy glue to the jig holds it all in place while epoxy cures. The wood screws are visible pinning the rear stays on. I used oversized holes and filled with epoxy for a little final adjustment. Upper and lower angle braces will be added to the rear stays next then filled with foam.
Two views of the bracing of the rear stays, top one shows dual top and bottom bracing, second view shows small cross bracing between stays. All wood to wood connections have plywood wafers inside. Note carve outs in braces to wrap around tube, holes drilled in aluminum for epoxy.
Rear stays with foam covering started.
A couple of spare wheels and a set of forks just to check clearances and measurements. I need to trim out more for the tire clearance and lots of trimming and shaping.
With the amount of sideways flex of the rear stays I decided to add something to strengthen. A 5/16" brass tube from a hobby shop proved to be quite strong for the weight. There are some small drill holes on the bottom of the tube for epoxy adhesion and is embedded below the top of the foam in a groove. Note bracket on inside of other rear stay for the coaster brake arm.
The wheel is done and looking pretty sweet. 8 speed Nexus hub on a Mavic F219 rim with stainless steel spokes with a coaster brake. Total cost was $550 with a special order Alfine tap shifter. Its a bit heavier than I was hoping but when the dérailleurs, extra chain is factored in there isn't much difference. The hub comes with two sprockets and are easy to change. One is a 19 tooth and a 21 tooth. Range of sizes available is 16 tooth to 23 so it can be a high speed cruising 8 speed or a more fun "play in the dirt" range can be selected fairly easily. Of course the size of crank gear will determine the initial range. Recommended crank gear size is 36 to 42 tooth.
A preview of the shape. A bit more tweaking in shape then the fibreglass starts.The use of small pieces of styrofoam makes for an uneven looking surface. It is much smoother than it looks. That line from the seat post to the bottom bracket is actually smooth and slightly curved. Once covered and painted the smooth lines will stand out.
A sweet Sugino crank. 42 tooth is the upper limit of recommended chainring size. Thoughts on the Project
This little section could change fairly often as the build progresses.
I like the shape and design. The balsa core is amazingly strong and light. Styrofoam works nicely for filling and shaping but the epoxy did not. It does not bond real well to the styrofoam and makes sanding and shaping very difficult due to its toughness. Maybe a silicone would work better. I would try to use a lot less small pieces and take more time fitting them exact to minimize gaps. It should have been two large pieces per side. 1/2" thick foam would have been much easier to work with also. 1" was just too much to cut away. I actually feel that using solid balsa without the styrofoam would be a simpler and easier way to go. The weight would be slightly more than the styrofoam but a wood glue could be used and shaping would be much easier than with epoxy. Covering the aluminum tabs with balsa would be harder but better results in the long run. It would need more strengthening at the higher stress points with carbon fiber or whatever. I would still use the epoxy adhesive for the aluminum to wood connections.
The 1/2" x 1" balsa for the rear stays was not strong enough for sideways flexing and needed to be supported with the 5/16" brass tube as an afterthought. It would have been nice to incorporate a light weight metal beam into the rear stay design from the start. Perhaps a square tube or angle bar. The brass tube stiffened it up enough. The balsa part of the rear stays will support an amazing load straight down but too flexible sideways, perhaps another 1/2 x 1 in a "T" shape on top and bottom of each stay would solve some of that side flex giving a heavier look.
The method of mounting the scrounged aluminum parts to the balsa with aluminum tabs and drill holes seems to be very strong. The only way to improve the strength would be more drill holes and a metal screw into the balsa with lots of epoxy. More careful trimming of the tabs would have prevented a bit of shape change to avoid hitting metal.
I have tried sourcing carbon fibre and is difficult to find here and is extremely expensive. To provide strength in bonding the aluminum parts to the rest I will be using aluminum screen strips under the the fibreglass. I figure on the high stress points three layers of screen embedded in epoxy resin and then 3 layers of fibreglass in epoxy resin will add plenty of strength. Most of the side panels will be just fibreglass. I will use 1 minute epoxy adhesive to secure the screen down before applying the epoxy resin. I will need to use an old axle to secure the rear stays in exactly the right position while I apply the screen and fibreglass. The left side rear lug is a bit crooked so I will use the resin to hold it in a better position. A 6" piece of threaded 5/15" rod with flat washers and 4 nuts should have been the starting point while doing the final assembly of the stays to the main frame. The amount it is out of align will not be a concern after the resin. In gluing on the aluminum screen I have been trying different epoxies. One is a marine epoxy that dries quite hard and is sandable and dries white in colour. It has a 2 hour set time. The 5 minute epoxy is easier to work with until you try to sand it.
Major note of interest, epoxy resin eats styrofoam as does fibreglass resin. I really goofed on the first coat of resin. It needs to be painted first. I just laid the first panel of glass cloth on it cut to the shape of the whole one side then started brushing on the resin. By the time I had spread out the resin I could see small bubbles forming under the cloth. A few minutes later and there is major amounts of foam being eaten. I don't know if this will leave a space behind the cloth but if it does I will have to strip all the foam off the frame and start covering with balsa then reshape. I will update the status after the resin hardens and see what I end up with.
After the normal curing time for the resin I looked at it. The foam dissolving mixed in with some of the resin and is not hardening. It feels pretty well dry on the surface but is quite liquid underneath.
This is after two hours. The resin did set up normally and the glass is hard but where the foam dissolved it sagged leaving no air bubbles. In places the sag is as much as a quarter inch deep. It will be possible to fill the low spots but at the cost of more weight. The other side will get painted with a latex before the glass is laid on it. It looks pretty bad but is savable. It will likely end up weighing as much as the aluminum frame by the time I get it looking right. This mistake will cost lots in terms of money, time and final weight.I'm posting this boo-boo so that nobody else makes the same kind of mistake.
After some consideration I am going to strip the cloth and foam down to the balsa core and cover it in solid balsa then shape it the same then do the cloth and epoxy resin again. By using wood glue for the balsa it will be much easier to work with and shape and sand and will not require any prep before the epoxy resin and fibreglass cloth. By stripping off the styrofoam I will be able to fix that design flaw of the flex in the rear stays hopefully without the brass tubing and still keep the shape the same.
Update - The fibreglass and foam stripped off down to the balsa quite easily leaving a thin layer of epoxy adhesive which chipped off easily. It didn't stick to the styrofoam or the balsa very well. It adhered to the balsa good if it was sanded first with 60 grit so all the new balsa will get sanded down enough to give something to stick to. The balsa is going on very nicely and quite easy. The large flat ares of the sides are pretty well covered in 1/2" and the rear stays in 3/8". Most cutting is done with an Olfa knife or a small saw. The wood glue dries pretty slow compared to the 5 minute epoxy but it does bond very well and is easy to sand. Probably about another 8 hours of work with the balsa. It makes me wonder why I didn't build it from balsa the first time.
The brass tubes on the rear stays were very well adhered and would have caused more damage than it would be worth to remove them so I left them on and added balsa around them much the same way as with the foam only better fitting. Some final shaping this weekend then I'll post a pic of it before I start on the fibreglass.
One idea I came up with is to stain the wood and do a fake faux woodgrain finish. It would show quite nicely through the fibreglass cloth and epoxy resin. Balsa doesn't have any real grain since it is so fine and straight. A high contrast of colours in the faux finish would allow it to show up even better. I would finish it off with a silver and blue wedge stripe with the decals on the stripe. A few large knots and swirls in the grain maybe something like a light coloured walnut. If it didn't look right then I would just paint it all sliver with a blue wedge as originally planned. Elsewhere in this forum is a bunch of pics of some faux finishes I did on furniture. It would be nice to "advertise" that its a wood frame and show off the uniqueness of it.
One nice thing about stripping it down and building it back up with balsa is that I left the axle spacer on the rear lugs the whole time and it straightened out the crooked lugs. I will put the axle spacer back in before the fibreglass part starts and that will strengthen the stays even more and keep them straight.
Balsa pretty well complete. A bit more shaping left.
Some light weight body filler putty has been applied to the ends of the balsa to smooth out the transition to the aluminum. Easy to sand and shape and little weight once dried. It will allow the fibreglass cloth to lay flat without any gaps behind. I have a large piece of cloth easily twice the length of the frame so I plan to fold the cloth then cut it to the shape of the frame and leave it connected at the steering tube so it wraps around at that spot. That will be for the final layer of cloth covering everything and leaving a smooth panel all over.
Finally got the first layer of fibreglass cloth on with one layer of resin. I did the cloth in one piece for both sides wrapped around the steering tube but I didn't allow fo the stretch of the cloth and it buckled up on the front of the tube so I didn't apply any resin there yet. So both sides are covered with only the inside of the rear stays left. The cloth wraps around and meets around the whole perimeter of the frame. That means I will have to use a 2" wide strip of cloth over the edges all the way around and blend in the edges later with sandpaper. Then a couple of coats of resin to smooth it all out to be block sanded before paint. I seriously considered the woodgrain idea but any more than one layer of cloth would be visible through the resin so the 2" strip would be visible. I could finish the resin then do the woodgrain on top but it wouldn't be as durable considering the different types of paint needed and the silver, blue, clearcoat and decals wouldn't adhere well enough. The original silver with blue accent stripe will be what it gets. Next photo when finished fibreglass.
Fibreglass is on with one more coat of resin to go. I have to block sand it down first. Having only played with it a couple of times in simple repairs my skills with fibreglass cloth are pretty slim so I have a lot of touch up to do. After it gets block sanded down close to level it will get a coat applied smooth then probably more block sanding and perhaps even some filler putty if needed before paint.
Fibreglass and resin finished. A bit rough in spots so some block sanding needed. A few drips etc. Regular "body work" from here, block sand, putty fill, block sand then primer, wet sand and finally paint next weekend for sure. Note cable buried under final coat. I completely forgot about it until before the last coat so I had to router a groove through the fibreglass then cover it in putty before that last coat of resin. For a giggle note the blue lines up over the top. I run the cable the wrong way cause it was upside down. Glad I noticed it before the router.
Its block sanding down pretty good. A bit of a grunt but it coming out nice and level and smooth after removing about 1/16" of resin.
As what is becoming a common theme for this project I am now another day behind. In my haste to get the balsa done I did not fit crank and wheel with chain to check for clearances before fibreglassing. Damn. There was considerable chain rub in a few spots so had to cut away fair amounts of fibreglass and balsa to make clearance. A slight change in shape but not much with a relief cutout around the crank. I also had to reroute the cable housing leaving more of it exposed also leaving a cable housing wide groove across a wide section which had to be filled. So after a burger and shake I'll get back to it and hopefully get it in primer tonight.
I also found out that the Sugino crank will require a 1/8" chain to be compatible with the Shimano sprocket on the wheel and the Messenger 42 tooth ring which is for a 1/8" chain and Shimano is 3/32".
Finally in primer. A scratch filler sandable thick coat primer that does wonders for small imperfections. Still a few minor spots to touch up tonight then paint tomorrow.
Cablehousing is held in place with a metal staple at each end. Staple is krazy glued into two small holes drilled on either side of housing. This will prevent housing from pulling out, ripping resin, paint etc.
First coat of silver went on and it looked like crap. It brought out every little flaw in the primer and below. So its back to fill and block sand. If I want the paint to look good it will require some more work and time. Add another week to the build.
Beautiful in Silver. A few minor flaws here and there but I'm tired of mucking with putty and primer. That is 3 coats of Chev Bright Silver by Duplicolor.
Decals and blue stripe tomorrow them lots of clearcoat lacquer. Assembly on Sunday.
A note about the vertical dropouts. I stayed with those and when I mounted the wheel and measured and cut the chain it worked out perfectly with no adjustment needed. I bought a half link in case I needed it but didn't. Pure luck there.Thoughts for the Future
Due to my age I am considering going to an electric assist system in a couple of years to take a bit of stress off the legs and make longer distances easier. At that time I will think about building another frame incorporating battery storage into it. I hate the present look of electrics with a rear carrier or battery pack strapped on somewhere so want to hide them inside the frame. I would likely go with a front wheel electric.
To build the frame I would go much the same route as this one minus the styrofoam diversion. The balsa works very nicely and the fibreglass and epoxy resin work quite well so those materials would be used next time. I would start with the balsa core designing for strength then cover it. I ended up with a larger looking frame than I wanted due to adding some simple streamlining around the bottom end so would want the next to be slimmer looking.
The decal sheet. The main decals could have been a bit smaller and the Nexus 8 decals could have been a bit bigger.
Decals and clearcoat finished. I think the main decals could have been a bit smaller.
Closeup showing metallic maroon stripe added as a late idea.
Time to assemble.Yeehaa!!!
After 7 months of planning and building it is finally done. The frame feels amazingly stiff with no flex and feels real good. The Nexus 8 speed works very nice and makes shifting smooth and quiet.
Was it worth all the time, money and work? I will post an addition to this post in a week or so with my thoughts on it all after some seat time.
But today I spend enjoying this new bike. Time for a ride.
After a one hour ride I must say I am pleased. It rides very smooth and tracks straight. I kind of grimaced going over the first curb but it handled it real nice. It was nice to bounce off a curb and not hear the chain rattling. There isn't much flex if any and feels very solid. I rode it pretty hard too.
The Nexus 8 speed seems to be pretty good. I find the overall gearing a bit low maybe so some seat time will tell if a sprocket swap is in order.
A thought on swapping sprockets, due to having no adjustment for tightening chain I have to make the chain length exact. When I swap to a smaller sprocket the chain will be too long and loose. I will simply pick up another chain and make it fit with the small sprocket and have matching chain and sprocket sets. Because the dropouts are vertical and no chain running through the rear stays the chain doesn't need to be split to remove it. I can drop the back wheel and swap the sprocket and chain in a couple of minutes.
A few minor adjustments like handlebars and the front brake is squealing a bit and bring the tire pressure up to around 80 psi, 40 psi was ok for testing. Tomorrow it gets the real test to work and back, 30 minutes each way.
After a return trip to work, the bike performed amazingly well. The Nexus 8 is real nice to use. There is some gear noise inside that gets amplified by the balsawood and makes it noticeable but still quieter than the dérailleur. Energy use is greatly reduced compared to the old Crank Monster, I found my legs and lungs were much happier. The Nexus 8 gearing ratios are not evenly spaced. I read some complaints about the ratios on forums and blogs but I find them well matched. The 1st and 2nd are like on the smallest chainring of a three gear crank. 7th and 8th are like on the biggest chainring and 3rd to 6th are like on the middle ring and those middle gears are spaced fairly close which allows choosing the right gear for your ideal pedal cadence in the average cruising gears. With the 21 tooth sprocket and the 42 tooth chainring I have gearing ranging from the lowest to about the 24th or 25th of the old 27 speed.
The old Crank Monster donated a couple of parts to its successor. The forks and front wheel, Forks are quite soft and not downhill type, good for commuting, handlebar stem and seat and seat post.
I found many things wrong with the old beast. Bottom bracket bearings were just about non-existent, the rear shock mounting plates have oval shaped holes and quite sloppy, pivot point of swing arm bushings sloppy. Front dérailleur not working at all, rusted solid, in fact shifter seized last year and cable was removed all due to lack of use. Rear wheel bearings rough and noisy, derailleur sloppy and worn out, V brake arm bushings worn and sloppy, peddle bearings grinding and sloppy and rear shifter getting sloppy. Lots worn out but thats after 8 years of commuting all year long. It served me well. I put $1400 into $500 bike and this new one I have $1300 into it. Hopefully I can get at least a few years out of it.
After a couple of days riding I found a few small cracks. Nothing real serious but cracks none the less. One is around the brake arm bracket and one on each rear stay right where the fibreglass meets the aluminum of the dropout. After noticing these I rode it the rest of the way home real hard and bouncing over curbs like my normal riding style and it didn't get any worse. I dribbled some Krazy glue into the cracks to keep them from chipping the paint. If they do not get any worse then I will just sand down the sharp edges of the cracks and mask off and throw some silver paint at it. It is possible there was some stress there from when the fibreglass was applied and it shrinks a bit. It doesn't seem to affect the structural strength since all the strength was built into the core and not dependent on the fibreglass. I'll be keeping a close eye on those cracks. It still rides good and feels solid. If the cracks do get worse then I will drill from the back of the dropout forward into the stay about 6" and epoxy in a threaded rod probably 5/16" or 3/8".
The next frame will have some improvements in that area. Crank Monster E ?
Commuting for a couple of weeks now and the bike is still amazing. No further cracks or worsening cracks so they will get touched up. There is a noticeable difference in efficiency. The only problem I have is my own physical limitations. My back has been bothering me for the last week and with a pinched nerve my legs always feel like I just finished a 20 mile ride. Even with the noticeable improvement in efficiency I have been struggling. I'm hoping the back problem heals itself quickly and gets me back to enjoying my ride. But it made me think about the future. I am peeking at 60 years so I am now planning to start the electric assist frame fairly soon. Designing is going to start right away. Sort of a "winter" project if it takes that long. With what I learned building the balsa frame it will have all the improvements I've learned and wanted. It will be a much sleeker and smaller looking frame with battery storage built in. I plan on going with a front wheel motor so that I can keep the Nexus 8 speed for normal biking and click on the motor when I need it. Kits are available with a complete front wheel and all that goes with it ranging from a few hundred up to over $2500. There are also choices like full electric, peddle assisted and combinations of those two. I will go with a system that is a combo, peddle mostly with electric assist for hills and against the wind. I don't need a long range and a longer range means more batteries and more weight. I would like the bike to be still useful without using the electric and not weigh a ton. The debate on which battery is best is still ongoing. The main choices are sealed lead acid and lithium and NIMH in 36 and 48 volt and 9 Ah to 15 Ah. 8 to 12 lbs. is pretty normal. I will likely end up with 36 volt and 9 Ah which is still enough to get me to work even with lots of "assist". Further research is needed before I make a decision. The lead acids are just plain heavy and large. A 36 V 9 Ah lead acid pack weighs 17 lbs. A Lithium pack of the same rating weighs 7.7 lbs. Pricing is noticeably different as well. $190 for the lead acid and $390 for lithium. NIMH batteries are the tops right now and a 36 V 9 Ah pack is $450 and up. NIMH and Lithium are pretty well equal in size and weights. So you could say $200 extra to weigh 10 lbs less. Size is 8" x 6 x 3.75 for lead acid made from 3 cells and the lithium is made from D size probably and 30 cells. The lithium would be easier to hide in the frame by removing them from the pack and wiring them all together allowing for a variety of shapes to suit the frame dimensions and keeping them near the bottom for the lower center of gravity. There is also the electronic controller box that is near as big as the batteries and a charger built in to consider. The control box also needs some form of cooling and allowances for all the wiring between controller and batteries and to motor and throttle / switch on handlebars. The cable housing for the Nexus will be buried along with the wiring in the first stages of the frame build. A waterproof Molex plugin on the frame with a flexible strain relief on the cable for the electrical seems the most sensible way to go.
For the aluminum parts I think I will cut up the original Crank Monster but make a few changes to how its cut. The rear dropout tabs will be twice as long at least to strengthen the back end more and the other parts will have longer tabs as well. I am looking into some type of hard wood for a couple of pieces of the core just for added strength even though the all balsa is amazingly strong. The seat post to bottom bracket and the bottom rails of the rear stays. The frame will have to be tough because at 20 mph on a bumpy bike path I do not want the thing breaking up and being the crazy old-school nut that I am, I am sure that eventually the batteries will be upgraded to 48 volt (or more) and close to 30 mph (or more).
Much planning and research to do.
The Crank Monster E is definitely in the works so a new post will be started for it.
Disclaimer: I fully support anyone trying a build like this but I am not responsible for for anything built using these methods.
That said, please feel free to use whatever ideas, drawings, photos in building your own.
I welcome any thoughts or questions on this bike.
Update : Its been a few years since the frame build. The cracks that showed up have not progressed any worse, in fact I now know it is the spot putty I used to fill in imperfections before paint being far too brittle with no flex. I dribbled Krazy glue into the cracks, sanded them down a bit and touched up the paint. Where I routered a groove for the shift cable has cracked and been touched up a few times. I hurt my shoulder at work 2 weeks after finishing this bike and had to quit riding till the next summer and then slowly back into it so the bike has maybe 1000 miles on it. It was meant to be the next all season commuter and expected to last 5 to 7 years of daily riding with 5 to 6000 miles per year. This winter I plan to strip it down and lay a coat of resin over the whole frame, sand, prime and paint which will eliminate any further cracks. I will redo the decals as well, making the Crank Monster II a bit smaller and the Nexus 8 bigger and the blue and maroon stripes a bit wider. The Crank Monster E is on hold till the prices for electric systems come down a bit more. Driving a company vehicle I can not justify putting a few thousand into a bike that will only get occasional use. Maybe in time for my retirement years.