G2 (GRC Rep) 50cc Banshee Conversion and Flex frame

After trying multiple styles of pocketbikes and never really felt comfortable I decided to start building my own. I am basing it on the G2 (GRC RR rep). The geometry is basically the same and decided to design and build a rear triangle that flexes like the Euros. Now being 125lbs, the material used with my calculations gives me roughly 1/8" movement at the rear. Also by changing to aluminum, I have lightened this bike 9.6 lbs thus far. I am expecting a 13-15lb lighter than original.

I also added an aluminum front end with hydraulic's and is much lighter and the steering response is so much quicker. I have pretty well customized this bike for my riding style and feels awesome.

This is normally a reverse motor but found enough room with some slight frame modifications and installed my Banshee motor. I just installed a 21mm carb and is a rocket.

Now for the test.

I was nervous for the first couple of laps but pitted and changed to a 7/60 gear and now was at 52mph. Cornered like a Euro went perfectly straight and no failures other than slight loosening of engine bolt and a few others.

Here are a few pics and testing of my bike on the track. I have never rode this bike prior to this video other than straight line testing. Check it out

http://img1.putfile.com/thumb/9/25304102032.jpg

http://img1.putfile.com/thumb/9/25419271127.jpg

http://img1.putfile.com/thumb/9/2541927129.jpg

Click below to watch the video

Click here to watch Mosport-frame-test

nice stuff! :P

Its so good to see original stuff on here. Top marks from someone who appreciates how many hours of hard work and head scratching went into that. I was thinking as I watched the video how fast you were closing on those a/c cags and how much of a mess one of those novice riders could do to your pride and joy. maybe fit an air horn? Keep us posted and be careful out there.

Thanks guys,

I appreciate the positive comments. I know I am not DM or BMS but I know I can make a complete light weight race frame with a flex design that truly works. The main frame is still steel and will be finished in aluminum soon. I wanted to make sure the rear flex design would hold up and did with flying colors.

As for the slower riders, my rule of thumb and is 98% correct is stay to the inside of a left turn passing newbies. They always want to stay wide and cut in. Also before going on the track, the Newbies were informed not to make sudden moves if they hear another faster bike coming up on them. I will be safe... Always.

I will post some future upgrades and will post a helmet cam video showing the rear triangle flexing in real time.

I just want to add that this setup bolts directly on the G2 frame. So if someone has the bike they could just add the parts without no hassel. I plan on making the Polini 911 frame next but from 6061 heat treated aluminum not the cast crap. I will keep the same geometry but will create a little more handspace and openings for easier access.

I really enjoy creating my own designs from the original. The finished product will be polished aluminum and am looking into annodizing. I make a ton of aluminum parts already and have saved a ton of money by doing so. Well, maybe not. I have spent alot but the ability to make your own stuff does save $1000's in the long run. I just want to add the parts are brazed not welded and keeps more strength opposed to welding. I also do a final heat treat process. I have not seen 1 aluminum brazed frame yet. Not easy to do but if done correctly is stronger than the aluminum itself.

I have a few more rear triangle designs in store and will build 3 prototypes of this type of frame (G2)

I just finished the rear 6" hydraulic brake conversion and works beautifully. Easy to modulate and stops on a dime without lockup.

Here are a few pics.

http://img1.putfile.com/thumb/9/26216435413.jpg

http://img1.putfile.com/thumb/9/26216435417.jpg

what benefits are you hoping for with that "flex design"? racing motorcycle frames are designed to be as stiff as possible, because flex in the frame weakens the bike's response to the rider's orders.

the pictures are a little small....

r

You forgot to mention that all motorcycles run a suspension. Pocket bikes do not. Also in having a 28" axel to axel, flex in the design smoothens out the rough spots and keeps the tires to the pavement. The rear triangle is the only part that flexes and that helps keep the tires glued.

You seem to be a little weiry about a flex design so BMS and DM are doing it wrong too I guess.

I would be more than happy to put my design up against any bike out there and have raced DM's and BMS's with success so I know I am the right track.

Sorry about the small pictures

Nice job. Would love to see some better pics but, i am sure you are worried about some one stealing the design.

Brazed alum huh? Is that the alum rod you can buy and use with a propain torch?? I tried that stuff and was amazed on how strong it really is.

Keep up the good work.
DK

I believe these pictures will give more detail. Sorry about the small pics.


http://www.putfile.com/pic.php?img=3451096


http://www.putfile.com/pic.php?img=3381831


http://www.putfile.com/pic.php?img=3381832


Much better.

I just worry about the flex and aluminum. If you are flexing aluminum your are fatiguing it. It isn't a matter of if it will break, it is when. Aluminum doesn't give away nicely either. It usually just snaps with no warning.

What kind of stress is the swingarm seeing? With 6061-T6 you can get away with 16Ksi for quite a long time, ~1 million cycles. Once you go over that fatigue life drops very, very quickly. At 25ksi you are under 10,000 cycles.

I would also avoid anodizing it. Anodize reduces the fatigue life by 1/2. The anodize layer cracks easily since it is very hard. Those micro cracks create stress risers that travel down into the base material.

I've had a lot of experience with fatigue and aluminum. I design underwater autonomous vehicles with aluminum pressure housings as my day job

The flex design does have a lot of merit though. You need to soak up the bumps some how.

From my testing with my weight 125lbs /bike 44lbs I am having no more than 1/8" flex. That is way in the "flex" boundaries in aluminum from my understanding.

I understand the pros and cons of aluminum and a flex design. I appreciate the input and expertise.

With such small flex I seem to think that the Aluminum is much more predictable than steel where you focus more on rigid. The steel bends and stays that way where as the aluminum springs right back. Plus it is much lighter and that in PB racing is a big+.

I believe the setup I have is safe and will continue to be safe for many more races to come. I know all aluminum has a short life expentency compared to steel but is worth the weight savings, comfort and handling overall.

I raced mountain bikes and would purchase a new Aluminum frame every 4 years beacuse they would warp from all the banging, dropping and twisting.

Again banzairx7, I appreciate the input and will keep everything you have mentioned in mind.

anodizing , is used on big bikes for some time. more stress on them then the little turds.
i saw the bike first hand this weekend , good job mnkay

I just proved the anodize fatigue this week. Took two identical tubes, 2.250" OD X 2" ID. One anodized, one not. They were pressurized internally to 3,000psi. Anodize one failed at 2600 cycles, unanodized failed at 9,000. Wether or not someone is doing it doesn't mean its right. A full size bike frame isn't flexing either.

Don't get me wrong I think this whole idea is great. Just giving some pointers on getting the best life out of the part.

Thanks my devilish friend. By the way, got the carb tuned and fouled a plug and couldn't run it. Did not have a spare (thought I did) and had to go home. Thanks for the carb help.


I appreciate the input guys but do not think I will be annodizing the frames anyways. I did think about it but I will powder coat them or polish them nice and shiny.

Will keep you updated and thanks for your expertise guys.

please post better pics!!!!!!!

I did... Look at page 2.