First scratch build, off road mini bike.

[jared8783]

Really important question that I can't find an answer to. The maximum distance from center to center of driver and driven pulleys on a 20 series symmetrical is 12 7/8' correct? I would like the pulley as close to the engine as possible since I will already be crammed for space. This is for the 7" pulley, lowest gearing of course. Since I plan to run symmetrical does the pulley need to clear the cylinder head? Does it need to clear the valve cover? And I'm wanting to run symmetrical because it has the lowest gearing.

Also I plan to surely run two jackshafts. One coming through the driven pulley, and one after that. Then from the second to the tire. This is because this is to be a work horse of a mini bike with really low gearing. I have already done the math for the sprockets and have the gearing numbers for both 11.68 mph top speed and 21mph top speed. I also plan on doing my best to run both gears on top of the cvt. And I will be perfectly satisfied even if i have to come to a complete stop and shut off engine to make a shift. Even If I end up running it as a one speed, I will still run two jackshafts to reduce gearing unless someone has some suggestions.

I saw these things at tractor supply the other day.
http://www.tractorsupply.com/en/store/nova-jaw-coupler-3-4-in?cm_vc=-10005
I think I could use a combination of these, idler sprockets, and two jackshafts as explained earlier, to make it a two speed on top of the cvt. Though I will surely need to come to a complete stop and shut down the motor to stop. But that's perfectly fine with me.

Like I said earlier this will be a purpose built bike. These are similar to the first two speeds on a rokon (and no I don't expect rokon performance). I went to a great off road park for the first time with a friend recently. Camped their all weekend. They allow camping and fishing and all sorts of stuff. They pretty much tell you you can do what ever you want. 750 acre park. I want this bike to get me to camping spots that cars can't reach. I want it to get from point a to b in the park. I want it to pull good logs for fire back to camp.

Most say not to run shocks on a project like this. But I really want to, and I sure will on the front. I have shocks for the rear but may decide against that and use just one of those shocks and suspend the seat or something, who knows.

Here is the crappy cell phone pic of the mock up. For all practical purposes the only four tubes that exist are the two on top and bottom running parallel from tire to tire, the rest are just holding those in place. The following numbers are very aprox. Ground clearance 9-13", seat height 25-30". and I would like to keep the wheelbase below 43 inches if at all possible.

And yeah thats the secondary purpose to this bike. Portability.

Thanks for reading and please I need some good advice here.

 

[landuse]

Have a look at thiese links regarding center distances

Comet identification, installation and belts
http://www.gokartsupply.com/identify.htm
http://www.gokartsupply.com/tcbelts.htm

 

[TANKSAREUS]

Nice - I always liked fat tyre build

 

[robbie]

http://www.mfgsupply.com/gomini/gominisprockets/gominisprocketsdrive/gominisprocketsdrive58b40.html Using the 8 tooth and the 17 tooth sprockets you can get slightly better than 2:1 reduction. Combined with this 2:1 shaft the starting ratio of a CVT is low enough to go up a very steep incline or pull a log. At this gearing, the limiting factor is going to be traction.

Try this logic flowchart to get the most pulling power out of your bike. There are three factors affecting pulling power: tire grip, overall weight, and gearing.

Let's say you have a bike attached to a log, but it's peeling out. You need a lot of tire contact, so you use ATV tires. The more rubber you put on the ground, the more you can pull. So you get the biggest tire you can find. Maybe you've already reached that point. You have some pretty big tires in your photo, and I'm guessing you aren't going to get bigger ones.

Now your tire peels out again. The only way to get more traction with that tire is to add weight to the bike. Once you build the frame, add your extra gear and luggage, and sit on the bike, that's pretty much your top weight.

The last factor is gearing, and it's a subtle point, so don't miss it. If you try to pull the log but your engine bogs down, you need better gearing. Also, if your engine can handle it but the tire is spinning like crazy instead of pulling, you need to slow the tire down. Both situations are remedied with lower gearing. But there's a point where gearing any lower will not do any good because of the traction limit set by the first two factors, tire grip and overall weight. You want to gear low enough to match the limits of the bike's traction, but not lower because it will make the bike slower with no further performance gain.

Unfortunately, this is one of those situations where you are building something weird and nobody has any first hand experience to give you gear ratios to start with. So you have to decide whether to use off-the-shelf components or get really crazy and build a bunch of radical parts yourself. Looking at what's available, you could use a CVT with an 8 tooth output, driving a jack shaft with 17T input and 8T output, driving a 60T wheel sprocket. This creates a 14.17 : 1 ratio, not including the CVT. Multiplying by the CVT's startup ratio of around 4 : 1 would give you a ridiculously low ratio approaching 60 : 1 before the CVT starts to shift. Surely that would be close to the absolute limit of your bike's traction, I would guess. Assuming 4000 RPM on the engine and a 1:1 ratio at top CVT speed, this drive train will give you a max cruising speed of just under 17 mph. This is pretty cool, considering that you can build it with only a CVT, plus one jack shaft, driving the wheel sprocket.

If you build it this way and find that you can't use all that torque because it exceeds your bike's traction capabilities, you may want to swap gears for more cruising speed. In that case it would be a simple matter to switch from 8T to 9T or 10T on one of your drive sprockets, or change the 17T driven sprocket to a 12T or 14T, without totally redesigning the drive system.

 

[jared8783]

Yeah im scared to run less than a ten tooth because ten is the smallest i can get fir 3/4 shaft? I really dont want a 5/8 shaft since the engines shaft is 3/4 i dont want to drop it. And yeeah the two gear ratios im shooting for if i do a two speed set up are 10:1 and 20:1 roughly so your ratio is right in the middle.

 

[mckutzy]

Hello, and welcome.

I have been doing some research on these things the last couple of years. I think I can be of some help or at least give a better perspective on thing to look at.
This type of clutch is typically used on large machines in lumber and other type of mills.

The best way I can think of doing this, is having dual rear chains, but if you have space then use a layshaft and single sided drive chain.

The trans you're describing is called a dog clutch.

It can be "done" using those love-joy flex couplers you describe. The major factor will be how the center coupler(s) (it has the shifter yoke linkage connected to it) slide well on a single splined shaft(eg. a keyed shaft). The splined shafts on a transmission of a vehicle allow the gears to shift smoothly latterly with the torque applied.
With the keyed shaft, you will most likely need another keyway milled into the shaft to have a stable shift with out binding on one point(180* opposite). The shifter will be rotating with the shaft, but allowing to slide and distributing the forces.
The shifter couplers will have to be relieved a thou or two(they are meant to be press fit on the shaft) in order to slide properly. You most likely will need to have them brass sleeved for a better smoother shift without allowing them to bind. Equally speaking the sprockets will most likely need to be sleeved aswell and the keyways filled at those points(like a brass key filed with a rounded top to match the shaft) as they will be freewheeling on the main shaft and could potentially introduce increased wear at those points.

So if this doesnt distract you from your task,(I hope it doesnt) then this will be some things to think on.

I am very curious as to your results. Any more questions please ask.

 

[jared8783]

Yeah dog clutch. Saw some pics, didn't read really too much. Some dude did it in a go kart or whatever talked bout the pros and cons. I remember the pics saying dog clutch.
Anyways he basically did what I'm thinking...I think. And plus I was just randomly watching a vid on manual transmissions the day before and then I thought about my idea but could only thing to run hubs as lugs as gear selectors. Holes drilled in idler sprockets that are ran to the rear wheel. I thought about this for days and just couldn't think of something I wouldn't be happy with.

Then while I went on a mission to tractor supply to measure things and try to get ideas....i then saw these nova jaw couplers that i described earlier. Never in my life did I ever discover what I thought was the perfect part for the job in my life.

Oh and I decided against dual rear sprockets. While I first planned that i decided against it because I have to run a jackshaft on the driven pulley, plus another jack shaft after that for further reduction to get my MAXIMUM desired top speed of 20mph. I really don't feel I will be happy with that, nor with 10 mph so I want to set up both. I can run two sprocket on a jackshaft shared by the driven pulley. Just look at my fancy ms paint skills. Now the nova jaw couplers/dog cluch part is not drawn in. But what I want to figure out is the easiest way to stop. Now one thing I do know for sure is that I will come to a complete stop and shut off the motor to shift. This is a utility bike first fun later. This is the only way I feel I can have a reliable two speed bike. As of now I plan on drilling and tapping the set screw holes bigger, then into the shaft and running a bigger bolt. I will of course tap it. Maybe 3/16 diameter hole. This way the clutches get a much stronger and more durable grip that can be tightened and loosened many times in the woods with a single wrench.

But if I did have to pick one speed it would be 15 mph. This bike is meant to go on some serious trails and some serious hills. It is meant to get me to remote camping areas at an off road park called Haspin Acres just south of indianapolis. 750 acre off road park. Lots of vw buggies, jeeps, quads, dirt bikes. And they let you camp where ever you like in the 750 acre park complete with two ponds and deep deep woods. I want to access and camp in the deep woods and I will push this bikes capabilities to the max. I will test it thoroughly.

Oh and I have surely decided against rear suspension. Not only do I hear it's rather pointless, but I can strap things on the side on the bike easier/better without suspension.

But yeah for real. I am completely NOT trying to shift this thing while moving, or while the motor is running. What do you guys think of it now that I explained it better? Input? Ideas?

 

[mckutzy]

You explained it well the first time. With a cent clutch/CVT you dont need to completely stop or have the engine off in order to shift. Just slow down and shift, there will be a bit of chatter but not that much. Just make sure the shift lever is in a good catch so bumps wont disengage the linkage.

 

[robbie]

If you feel that you really have to make a two speed bike, wouldn't it be easier to use belts? Put multiple pulleys on the two shafts to make multiple ratios, with an idler/tensioner for each set. Select your speed by engaging one of the idler/tensioner pulleys.

 

[mckutzy]

From what I understand, the multiple belt driveline can do but there is a loss of torque from not having a proper tension. Its been done by one member here, he didnt have good luck with it. cant remember who or when abouts it was posted.

 

[jared8783]

Yeah and chains and sprockets take up much less space than belts too. And last longer.

And Mckutzy, could you perhaps link me to some more info on that? I really don't want to talk too much more in the thread about shifting on the go since I don't see myself attempting that. Though I am curious to learn more. I just figure that shifting on the go won't last as long for one and two just won't be as tough.

 

[jared8783]

Thanks for the limk landluse. So the maximum center distance is 12 1/8" for a symmetrical 20 series. Does anyine know for sore if this will clear the cylinger head? I did measurements on the mock and it looks like it will but it willbe close. I need to buy the driven pulley from someone with a good return policy in case it wont clear the head or valve cover. And it is important to me to run symmetrical since it has significantly lower gearing than the asymetrical.

Where is a good place to buy the pulleys? Way i see it this project is waiting for me to build the base of the frame, the drive system, then build the rest of the bike around it.

 

[loud1]

I'll tell ya that suspension with fat tires isn't very important, my bike hits 30 and i don't get shaken up too bad.

 

[landuse]

Thanks for the limk landluse. So the maximum center distance is 12 1/8" for a symmetrical 20 series. Does anyine know for sore if this will clear the cylinger head? I did measurements on the mock and it looks like it will but it willbe close. I need to buy the driven pulley from someone with a good return policy in case it wont clear the head or valve cover. And it is important to me to run symmetrical since it has significantly lower gearing than the asymetrical.

Where is a good place to buy the pulleys? Way i see it this project is waiting for me to build the base of the frame, the drive system, then build the rest of the bike around it.

I have no idea if it would clear the head, but you can buy TC's pretty much anywhere, from ebay to CL to BMI

 

[jared8783]

Yeah i can buy it from lots of places...but i need a place with good return policy in case it wont clear the head.

 

[machinist@large]

Have you considered using a four speed Peerless gearbox out of a lawn tractor for your range box? Doc Sprocket, one of our moderators goes into some in depth detail of how to bullet proof one of these, and you've already stated several times that stopping to select the correct gear doesn't bother you.

The thing that has me thinking you might like to look into one of these is that for non racing applications, you could go with the stock grease lubrication, thus giving some options for mounting orientation, four forward gears PLUS reverse, and they are compact; about the size of a large Cantaloupe/ baby Watermelon. Add in the fact you plan to use a TC for the clutch, and you would then have some nice over lap between ranges (did I mention that you would have reveres as well?).

I don't know if this would be the right path for you (it's your project, which means you have every right to build it your way). It's just that as I was reading through this thread, it occurred to me that this might be a potential solution, and one I think I might look at come spring after I find out how bad the damages are going to be on April 16.....

Hope this helps..... Pat

 

[mckutzy]

For the ease of use and lack of need to engineer a good mounting solution without shafts ect. the gearbox is would be the way to go.
A bit more expensive and trickier to find, but the hassle is worth it in my bet.

 

[robbie]

Yeah im scared to run less than a ten tooth because ten is the smallest i can get fir 3/4 shaft? I really dont want a 5/8 shaft since the engines shaft is 3/4 i dont want to drop it. And yeeah the two gear ratios im shooting for if i do a two speed set up are 10:1 and 20:1 roughly so your ratio is right in the middle.

I wouldn't worry about a 5/8" shaft causing problems. You won't be able to stress it enough to break it. Your biggest issue is going to be tire slippage.

 

[jared8783]

Ok so im plannin on using the jaw coupler for the sprocket engagers. Now i will need one of them welded t each idler sprocket meaning i need to turn them into idler jaw couplers. Will have to bore it out to fit a bearing that will fit over the 3/4 shaft. What do you guys think? Suggestions?

 

[mckutzy]

Typically there is enough room to fit the sprocket on the coupler. So I would turn down the coupler to fit the sprocket(a weld on sprocket, that's meant to fit a weld on hub).

I don't think there is enough meat to have a bearing fitted in the coupler properly, unless you want to get fancy and get some thinner roller bearings. For all the work it will be doing a bronze or brass sleeve would do.