52cc Stage 2 CAG CVT powered X-Games Motobike

Thank you for another one of your valuable responses lowracer! Another good thing about freewheel is that prolonged engine braking seizes 2 strokes. I plan on using a BMX freewheel. I'm glad that it will take off reasonably well with a 15.6:1 ratio on large wheels, that means the BMX will probably work great with a 10.3:1 ratio. That gives the option of the CVT or the geared hub. It seems like putting both on the bike is pointless.

I really can't decide. The CVT will be smooth, the Sturmey will be fun to click through.

I might save the Sturmey for a lower powered build, like a china girl. While the internal design of the S3X looks a lot stronger than the SRF3 guts, I worry about letting somebody ride the bike for fun or to sell it, and them speedshifting through and blowing the hub. I don't want to make people sign a contract to ride a bike. I think manual transmission is probably better left for a racing inspired bike or a happy time build. I still don't know how to ride a manual dirt bike lol! The Sturmey grip shifter seems like it's the easiest to use at speed, but also the easiest to have maladjustment, which can kill a hub quickly.

It's really so hard to decide, the complexity of the build depends on if I plan to sell the bike to somebody else. I tend to go all out, and to do so might not be worth it since it sounds like this motor will have "adequate power" lol.

I've got a bunch of fun build ideas in the works. I know I'll become infatuated with those and ride them to do testing before I sell them. I want to have one bike that I keep as a daily runner, and it seems like the KTM clone OCC will be the best for that. This bike seems like it will be insane from what you say lowrider!

I wish I could pack all the best stuff together like a KTM50 with a geared hub, but they'd all probably break. It seems like Lifan is where it's at for big power and gears. Sturmeys are okay with HT's supposedly, with reeds, a Hi-comp head, and expansion chamber would probably make enough power to run into issues. It's hard to tell what is a well engineered system when they won't post specs for the max torque handling of any bicycle stuff. Makes it hard to decide whether you're making something that will last.

I think I'm going to save the geared hub for if the bike feels like it needs it. I have a feeling it won't!

There is another 20" bicycle build that I'd like to do using a Cag engine, so I think I'll use the geared hub as a jackshaft on that since the torque loading is lesser if used that way due to the higher shaft speed. I also like the idea of having a really short cable to the hub from the shifter, I've had problems with bind and bend causing it to stick out of adjustment.

I had a cool idea for belt drive for the next build since it will be a hard tail. Incorporating some kind of drive belt or rubber damper into the drivetrain of every MB I build from now on will be a priority, for shock absorption. The next bike will be more of a racing bike than this one which is oriented toward commuting with good handling and ride. I'm gonna try to make a Sturmey suicide shifter into a foot shifter for that bike, with stronger gear detents.

SOOO I'm 95% committed to the CVT again, an auto trans is good for everyday putting around in town. I might not even need that ADA pumper carb if flipping the intake manifold around proves to get enough angle.

I'm trying not to play around in my living room with the parts too much to avoid scratching up the bike, since it's in minty fresh condition, lol.

Now I need to find out who sells the absolute widest bottom bracket cartridge and cranks, as I'd really like to have some pedals on this bike. With the centrifugal clutch, as long as I can keep it adjusted, there is a chance that I can put the pedals in the 8mm driveline from the CVT, there's minimal resistance from the tight spot in the belt, and would make it so pedals and gears can go through the same chain. Maybe incorporating a crank freewheel to prevent egg beaters if a clutch spring breaks or whatever would be a safe bet. I'm also looking for short crank arms, better for going fast and not digging in. They make them for BMX and unicycles so there should be something that will work. It would be cool to have some sort of pin that can lock the pedals in peg mode, then there's the best of both worlds! Should be easy enough with a slideable bolt, or pip pin.

As I write on here the ideas keep flowing, so I jot them down so I don't forget. Here's my idea for a unique engine mounting system: a custom press brake bent 1/4" thick aluminum plate one piece engine cage. The idea is to have some diamond plate aluminum water jetted and bent into the cradle, braced with aluminum strut rods and aluminum standoff tubes from the frame bolting points.

I was playing around with the idea of a Ducati Hypermotard style truss frame, but it's in conflict with the bike's design theme as a regular KLX110 type bike. If I farm out the work for the aluminum cage I can possibly make this something affordable for others that can find a Motobike and want to easily motorize it. Fabrication takes time, and I currently charge $30 an hour so you can imagine how much a welded steel cradle could cost in labor alone. Maybe a simple one could be about $150, if I can match that on the CNC manufactured one, then maybe it's a great option.

I'm going to pursue this idea with a mockup soon. I don't know how successful group buys are, but maybe I can arrange one if mine turns out successful and there is demand. I don't think it should be too expensive to run a quick water jet program and make two big 90 bends. Diamond plate is cheap and will be stong enough in this orientation if braced. I have a friend at a CNC shop that anodizes stuff all the time, that might be an option. I was thinking the standard engine colors would be good like red or blue. There's always tinted clearcoat to make it look anodized if the existing anodizing prevents dying.

Hah, thanks! Right now it's a total thought experiment. Everything is a compromise. I think this one is just gonna be CVT. Figuring out pedals on this bike might be impossible, but at least with the CVT I should have a reliable way to always get around if I carry a spare belt. The CVT at the output is wide, and will require a bottom bracket that sticks out about 10cm from the side of the bike. Maybe the widest ones from SBP will work, if not it's gonna be a noped.

I've accumulated parts, but having five bike builds swirling around in my head, it's hard to focus on getting anything done. Plus I'm in school, so I'm just planted at this computer daydreaming about combinations in between work. Until I graduate in a couple months I'm not going to realistically have time to get much done. I need to secure a shop space and then things will take off this year. Thinking about a hardtail bike to use this engine with for a fun build. Real progress will be made after December.

I've got all the pieces, now I just need a couple days of devoted time to the bike. I think it would be cool to have the water jetted engine cradle, it seems like an obtainable goal if I can find a shop with a big press brake too, I might know of a few. This will be good, I promise! You should all be scanning CL for your own $50 Motobikes

This is the approximate angle with level the motor will sit at.

It looks like I won't need to do anything really crazy to make this work, some simple aluminum mounts to the front of the skid plate, some spacers for the bottom engine mounts so I can get the filter on, and some simple mounts to the tabs on the top of the motor on the drive side. For rigidity it will probably require some braces of some sort. I have an idea for that too, by bracing the bottom mounting points and providing mounting points for braces toward the rear of the bike. I'm going to try to use as much reasonably thick aluminum as I can to make the bike lightweight. The CVT will provide additional mounting points for the motor toward the seat.

The pipe will hang pretty low, but its not such a big deal. This will be an on road bike primarily because I'd be strung up by nuts for riding a gas dirtbike offroad around here in Marin

I think pedals will be possible with some SBP wide bottom bracket cranks.

I might be able to get this bike running this month, probably should try to start it before the warranty runs out on the motor.

Lol, garage? I build these things in my kitchen and living room! I really do need a shop though, if I had one I'd be riding this right now.

I'm glad that my impulsive Ebay purchase of the skid plate was a good one, it'll make everything a lot simpler. I think I can avoid needing to go to the water jetter's now, and just pick up some materials at the hardware store.

I think if I were to go to the next SoCal racing event in 2013, this will probably be the bike I'd take because my OCC saying peekaboo in the first pic is heavy and has heavy wheels and tires. This thing should be 20-40lbs lighter and I'll use regular width tires.

As for appearance, I'm going to go with the anodized red theme. There are a lot of nice anodized bike accessories available nowadays for cheap.

I've got an idea of how can make these motors hybrid electric for reasonably cheap, less than $200 and 20lbs. It would be a mild setup with small AGM batteries as an assist to the gas motor, of less than 500w or 10A max, it looks like the internal wiring can handle that.


You can get these starter motors, they're supposedly not so great, but anything can be improved. The biggest concerns I have are the brushes because as well as an electric starter, it would be used at a higher voltage to assist the crankshaft while running with a combination mechanical and electric throttle. Cooling is an issue with these under extended cranking, so maybe drilling holes for airflow around the outside will help, along with hanging it in the airflow. I've noticed that overvolting surprisingly makes motors run a lot cooler under load, because they don't stall out drawing tons of amps. Maybe 48v instead of 12v will work if everything is optimized. The brushes are the same carbon brushes you can buy at the hardware store in the slide out bins, so it'll be a service item.

This is also a magneto, so some current control circuitry could make the starter regen on decel even with a freewheel, although less so than with a fixed sprocket to drag the rpm's up. If the regen becomes a major element, then maybe a fixed rear sprocket would be in order.

This bike could fit 4 12v 5ah SLA batteries underneath the fairings along with the gas motor easily. The total weight of batts would be about 12lbs. and the starter and controller about 6 total. I wonder if its worth doing? It certainly is an interesting concept, and I think that assisting the crankshaft will make a two stroke rip hard because it will fill in the lower end of the power band. Linking two motors with a common solid crankshaft means that their horsepower and torque is added together, so it would theoretically be better than with a separate electric motor. For racing there's even lighter, cheaper, 2ah batteries that would weigh about half as much. I'm thinking if this worked smoothly it would just make the bike more well rounded as a ride for around town. The acceleration would be insane, with all the power going through a transmission.

Whattya think?

You know what? Nevermind!

1/2 hp after losses isn't worth the complexity, I could bump the compression a point and get that! It wouldn't be able to run only on electric because it would fight the compression, and then obviously start the motor. You could hypermile one of these motors with this method and a freewheel. Stop the motor and coast downhill and start the motor with a twist of the throttle to continue powered. It would require 24v to get the motor really zipping for a stop start system, but a small capacity 24v pack would weigh little.

But wait, a stop start system would seize a two stroke if it stopped really hot. Scratch that idea!

So in reality the little starter motor would need to be pushing 1000w to really make itself worthwhile. I have no idea what the current draw of one of these starters is at 12V, it would be doubled approximately, either that or the voltage could be doubled. The poor little windings would smoke with the first throttle pull I bet.

Nevermind!

pedals? hahahahah, yeah.

the pullies inside are nicely machined, the case has vent holes at the top by the finned pulley

fits like a glove




The exhaust will require cutting and re routing, with some sort of block hugger header for ground clearance. One of the single outlet exhausts would work dumping out by the dropouts if it was a hardtail, but its not so it needs to go up toward the seat. This is in a way a good thing because the expansion chamber would never be able to be ported to the shape of the jug, with its rectangular outlet.

So I looked at the gaping hole on the trailing arm and wondered what I could do with it. I think I'm going to stick a high powered electric RC motor in there! The idea of having a hybrid bike is appealing, especially if one power source goes out. I can double the hp of the bike by sticking a little motor in the trailing arm, and maybe hooking up water cooling.

This way I could use the engine electric starter (if it fits) as a dynamo to continually charge the batteries at a trickle rate when the engine is turning. This power would then run the powerful motor. It would be like a plug in hybrid in a sense. The little motor dynamo probably has a small output but while cruising the batts would be charging, when ripping the voltage regulator would need to kick in.

There will be a lot of spare room on the sides over the engine, good places for batteries. I could fit those 12 lbs of AGM's in there easily and it would power the bike about 8 miles alone without recharging. Lead acid batteries can be charged at a high rate, or at least higher than the Li batts, and they're dirt cheap. this might be a worthwhile option, while keeping the bike still under 100 lbs!

These motobikes would be ideal as an electric freeride bike with a little motor stuck in the trailing arm like a Razor dirtbike. Its chassis weighs about half as much as one, and the new brushless motors are powerful.

It makes me wonder if I should put the Cag on another bike and make this electric due to the simplicity of only elecric. I actually have another idea for a bike powered with one of these motors so I could use it all anyways.

The hybrid idea with around 7hp but might be too complicated in real life. On the other hand, if it just works, you just plug in. I think 3.5 hp is worth a 20 lb penalty, but it will go against the whole lightness theme, although that kinda went out the door with the CVT. The electric motor separate from the engine but on the same chain would allow independent use of electric or gas, since the CVT can freewheel with the centrifugal clutch, and the electric motor can freewheel with minimal drag if is not being used in braking.

It would be a great engineering project, but is it worth the complication and weight?

Would be street legal in CA without pedals if it was a hybrid?

Electric bikes aren't required pedals in CA, and it would technically be an electric bike I guess, right?

I agree with that, but it won't have pedals because the CVT gets in the way, But I know of a powerful little motor that will fit where the 1 piece crank used to be in the swingarm. It would be a mild hybrid, with only around 12 lbs of AGM batteries or an equivalent LiFePO4 with twice the range or half the weight. The cost will go up by about $200-250 running the lead batteries, add $200 for Li. Keeping it simple is a good idea, but also having a backup or stealth mode would be nice.

I'm tempted to just do electric as a replacement for the MX1000 I'm selling, and maybe splurge on expensive batteries.

However...

The idea of a gas range extender if the electric stuff isn't too heavy is an exciting idea. Being able to ride bike trails without pedals by shutting of the gas motor would be really cool, and help me to get around easier in the bay

I kinda want to put this motor on a cool hardtail, but I dunno, a hybrid if I can't have pedals might make it CA legal and ease access to more trails on electric. My goal with this bike is making something that can do what my chopper turned bobber OCC can't, and one of those things is trails. Electric would allow light trails without making people mad. If the batteries came out easy then maybe the idea would be ideal, because they are the majority of the weight. If it malfunctions or you just want gas, taking the batts out would effectively turn it bac, and the tiny motor would become a low friction idler (no load unless charging).

I'm caught between building really cool bike ideas or buying equipment so I can build really cool bike ideas, it's going to get kinda costly to do both.

Cmanns, I think you should get a rear hub motor wheel, so the bike doesn't do funny stuff on loose surfaces or torque steer like you said. I'm sure you could drive the disc brake mount on a pie motor from a gas motor and it would work fine, and actually relieve some stress on your frame, dropouts especially. Front wheel drive is only cool if you've gotta drive to work in the snow, on bikes I can imagine it being borderline dangerous.

I'm not sure if I want to do it yet, fortunately its something I can add later if I remember to reserve space for batteries. If I hybrid the bike I'll use lead batteries because it would be experimental and I'm afraid of damaging a Li pack. With both drivetrains going together, the 7hp total would make up for the 20 or so pounds of extra crap on the bike. I kinda like a little weight if I'm not pedaling, because it helps the tires smoosh into the pavement better so I can lean.

The thing is, a this bike would make a superb pure electric, or pure two stroke, I'm not sure if it's worthwhile because I could probably get away with a noped if I ride carefully. On the other hand, it would create a shadow of a doubt about whether the moped is legal, and that's enough to avoid a ticket which could be quite big for riding a dirt bike in town without motorcycle reg.

My ankles are kinda messed up right now from sprains so while they heal I'd prefer to have to pedal a heavy MB if it craps. I'm not sure whether the electric motor would be powerful enough to go up a hill on its own, but I would think so if it has 3.5hp max, at low revs it must at least make 500w which is enough to move well without pedal power. Supposedly the moter I want to use runs cool already, and I'd be water cooling it as well with an electric circulation pump to a little radiator, so maybe it will be okay. The motor is supposed to simulate a supercharged v8 in a 1/8-1/5 scale speed boat or buggie, so I would imagine it has a decent amount of torque.

It's hard for me to justify allocating the money to it when I need to start a small business. I have a feeling it would be awesome too, so I wouldn't want to sell it. I need to sell my pure electric dirt bike and I'm having trouble doing it, because I keep modding until I fall in love. The hybrid or electric idea would be an attempt to make a better replacement for my modified Razor dirt bike so I don't miss it so much. There are a lot of trails that I have been able to get away with riding just because of the silent electric, and I don't really want to lose that.

I wish the swing arm hole was about 5mm larger because then I could fit a 7 hp electric motor in there. It's hard to ell whether a pure electric on this bike would be reliable or if I'd overload the motor that will fit in the bottom bracket hole. I guess I could mini jackshaft it somehow to a geared hub transmission.

The real problem is that the possibilities are really endless. It's hard to tell what components you're going to overload, and this bike is all new parts that aren't cheap. I'm pretty sure I want to use the cag on this bike, since I have a different motor planned for my next build. I was thinking about just using the motor for the other bike and going electric, but the charging time is a killer, so the only real solution is to charge while riding.

Of course charging while riding induces drag, but you can adjust how much drag there is by the load on the circuit, or the charging rate. The key to making a hybrid with onboard charging work right is power management, which gets complex. I think I can do it with analog circuits and a couple component boards. I don't really care if it doesn't charge up while riding, rather I expect it to just discharge slower as the starter/generator makes up somewhat for lost power. It would be like riding your pocket bike with the headlights on in terms of motor drag. When accelerating, the output of the small electric plus the cag would overpower the drag in the dynamo so that it would be a small fraction of the overall power.

Pocket bike guys take off the electric starters to get more revs and faster acceleration. While I can't really lighten the motor more since the rotating parts are copper wire and magnets, what's left is balancing. The reduction in redline from these must come from imbalance, so I'm sure some fiddling around with some vee blocks cold balance the motor with a drill or some solder. Not too worried about slower spool up of the motor, because the electric assist would shove the little reed 2stroke into its powerband faster, so it should in theory pull like a train.

The power management electronics would be another story completely, I have an idea of what might work but there is no guarantees with electric stuff, especially when you can't get a spec sheet or the intended purpose is different. I found a brushless regen controller for e-bikes, but the spec sheet they provided upon request looked like it was written by a six year old. None of it was useful info for designing a system. It's kinda frustrating because you have to make so many educated guesses with the components for stuff like this, and just hooking it up wrong can fry everything.

I guess the path this bike takes will depend on my want for a challenge when I get through some school stuff this month. I think about this too much and it distracts from important things, although alternative transportation is a career goal for me in engineering, so maybe its money and time well spent.

Well I recalculated things, because it all seemed too good to be true. If I want to use this particular motor I need a gear reduction of about 30:1 to have gearing that maxes out where wind resistance would at around 45 mph on electric alone. I can't figure how to get 30:1 in top gear even with a geared hub on a jackshaft, the best i can get with wild huge sprockets that would be a nuisance is 20:1. It would really require two jackshafts which is kinda crazy, not sure where I'd put all that. If I can figure out a method of chain reduction that would work so that top gear is between 25-30:1 then it will have sane gearing and actually work.

Turns out this little motor pulls a ton of amps, so it'll require lead acid batteries unless I want to buy two lithium ions to run in parallel $$.

I was so set on just making this electric, because I have some other ideas planned for the Cag engine, as well as some four stroke ideas. If I can get a solution for compact gear reduction, then this bike project will go electric instead.