GNG mid drive Trials bike build

Thought I'd start a build thread for my Trials bike project, I'm starting with a Planet-X jack flash which I built for urban trials and dirt jumping, I like the geometry of this frame.
Since I havnt yet recieved the GNG kit I started by adapting a 45mm wide 24" downhill wheel with a 2.75 tire to the frame, this is a brutally strong wheel and the 24" size will help lower the gear ratio. I then started mocking up the battery compartment and built a mold for the rear fender to give it a moto-trials flavor, last night I layed up the initial carbon fiber for the fender, the fender is still way oversize in the picture but gives an idea of the look I'm after, I'll also make a front fender of carbon using the metal cruiser fender as a mold. Untill I recieve the kit the battery compartment will have to wait but it will fit the 14s 2p lipo pack easily, I am thinking of switching the fork to a dual crown downhill fork and mounting the controller to it as you would a number plate, we'll see.
For the drive train I am hoping to get away with a 4 speed cassette with the lowest gears fairly close ratio and the higher gear for traveling, I want to do this to keep as good a chainline as possible, along with a double chainguide in front I am hoping to avoid chain drop completely .
I also want to do a chain drive privary as I see the belt drive being a never ending problem under high torque conditions.
So, the objective is to have a lightweight motor driven bicycle trials bike with Moto-trials flavor that can be ridden to offroad locations and still be fun to ride techincal trails with.
And so it begins.

I like the fender! Why a hardtail however?

subcribed.

bzhwindtalker said:

I like the fender! Why a hardtail however?

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Well, of the dozen or so bikes I have the Maverick and Gary fisher have floating BB's , the Cannondale super-v has a lefty fork and would cost alot to adapt, 3 29ers are all hardtail , two proflex frames that I dont like the looks of, Zipp track bike and a bunch of others are not suitable and I'm not going to put a motor on my pure trials bikes,







This one already has an engine, it was fun to build but its finished so time for a new project.


so, that leaves the Jack Flash, too many bikes to buy another for this project , I am used to hardtail for trials and I like the geometry.

Anyone needing a project frame to butcher? I have a ton of stuff laying around.

Yeah, I know, I'm a bit compulsive.

Yes Denisesewa, I'm afraid your compulsive obsesive disorder is now clinically moribund and a further bike would certainly prove fatal. Strongly suggest you pack up the bikes, wheels, the lot and send them to my address here in Scotland in a twenty foot container poste haste for safe keeping.

Nice project! I would not put pedals on a trial bike. You even go for a 1000W brushed setup (due crisp throttle response and simplicity) and use a fixed ratio like on a scooter.

For example:
XYD-14 brushed motor, 11T sprocket
37V lipo battery
40 amps, 1500W brushed controller
150T custom rear sprocket
custom motor on the bottom bracket, which is easy to make when there are no pedals
a #25 chain
a throttle - that's it

The GNG or cyclone would work too. Would still not be as lightweight as the brushed drive I guess.

Battery could be 10s 5000mah 25C, which weight about 1,3kg, can take a bunch with you and change them frequently, keeping the bike as lightweight as possible.

For best weight distribution, the motor should be placed just in front of the bottom bracket, though there would have to be a chain guide that protects the legs from the chain.

crossbreak said:

Nice project! I would not put pedals on a trial bike. You even go for a 1000W brushed setup (due crisp throttle response and simplicity) and use a fixed ratio like on a scooter.

For example:
XYD-14 brushed motor, 11T #25 sprocket
37V lipo battery
40 amps controller
150T custom rear sprocket

The GNG or cyclone would work too, but I would still throw away the pedals.


Battery could be 10s 5000mah 25C, which weight about 1,3kg, can take a bunch with you and change them frequently, keeping the bike as lightweight as possible.

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Well its a bit late to change plans now, the GNG kit should arrive tomorrow , I have 14s 2p turnigy 25-35 c batteries coming as well.
I did build a brushed MX some years ago with a 1200 unite on 48 volt sla's, it weighed over 100 lbs but the performance was good and it handled well, I locked out the pedals on that one >>
http://endless-sphere.com/forums/viewtopic.php?f=7&t=2930 <
Since I already ride trials bicycles I dont think the pedals will be a problem, in fact they may be a benefit and I want to be able to pedal it around town to different riding locations which is why I kept the seat with a long seat post so I can raise it.
As for gears I am thinking 3 cogs on the rear, 34t for low gear trials and two more higher for trail riding , am I close with 34t or do I need to go lower, like dropping the tooth count on the chainring? any suggestions on what gears would be appropriate?

Oh and if you ride trials and do jumps the stock BB and crankset will fail. It did it two times for me and i'm only 65kg, not trialing really hard either... However if we manage to get the gng reliable it will be such an amazing trial drive, so much torque and control!

the less gears you can get away with on the rear the better, I found when I was experimenting with driving through the gears that the ratios were not wide enough apart and was changing from the smallest tooth count as soon as I started moving and going straight upto the biggest tooth count. My bike would pull away in the biggest tooth count and have a top speed of around 40+mph and didn't really need to use the gears to be honest even for some technical climbs but it was nice to be able to have the option. I found it to be more of a pain as the bike needs to be moving to be able to change the gear, so if doing something very technical that required a gear shift mid way though that gear shift had to be made whilst moving and this was not always practical. I ended up just having a fixed gear of a max speed of around 25mph and this had more than enough torque to do everything that I could possibly want to do. I don't know what the GNG kit output rpm is or what sort of power it can output so the whole dynamics may change as the motor I was using which was I was running on 48v at 75A if it had outputted less power it would have been a little better/easier on the gears maybe and looking at bzhwindtalker's videos the kit do look more than capable. Just thought I would put my experiences out there about using the bike gearing as regards trials.

Finaly got me kit today, Installed the motor and started working on the chain guide, kinda cool that one of the holes in the BB sheet was in a good enough place and the perfect size to accept a chainring bolt.


I drilled and tapped a hole for the second bolt.
Everything lined up nicely. I also built the battery tray but cant go much further on that untill the batteries get here ( still at least a week out), mounted the rear fender and fabed up a mount for the front fender, lots of work left to get them looking good so I'll stay busy.


Since I have had time while waiting for stuff to arrive I have been mocking up a battery cover which would be made out of carbon fiber but I'm not sure I like it, seems like it makes it look like a scooter or something , maybe I'll go with my original idea for just a battery box within the triangle, I can always add a cover later.





A little bit of progress eh?

gwhy! said:

the less gears you can get away with on the rear the better, .

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I agree with you GWHY , I will probably try it single speed with several different gears but I have a feeling it will end up as a 3 speed, I plan on building a 3 cog cassette and use a front 3 speed shifter along with a 9 speed x9 derailiur and try to calibrate it to work together, we'll see.
"D"

Denisesewa said:

gwhy! said:

the less gears you can get away with on the rear the better, .

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use a front 3 speed shifter along with a 9 speed x9 derailiur and try to calibrate it to work together, we'll see.
"D"

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I hope that this will work. You will have to keep an eye on the lever at your derailleur. Even 7speed shifters do not work with 9speed derailleurs I would go for a 7speed derailleur and shifter and use only 3 gears. You can lock the rest (simply by using the set screw on the derailleur) and over paint the label on the shifter Much easier and has the same effect. STILL I would go for a single gear setup and overvolt it Also if you have the right torque the pedals disturb more than they help, also they weight...

ATM it looks like you use a 14T sprocket on the rear and the stock 12T front. You could throw this all away using a single reduction. THEN there would be no belt which will crack soon...it's also a quetsion of safety.I would not want to drive your build trial style.

Now that you have this motor and the mounts just turn it around and do a single speed chain reduction, like 11T #25 on the motor and 120T one the rear, you'll like it The setup you do now does only 50Nm to the rear wheel. That's NOT ok for a trial bike, that's wannabe. IF you go for the 11/120T setup, and use a 30amps controller you can still go about 35km/h top speed and have 120Nm that ROCK your rear wheel! You could also go for 140T for 140Nm or 180T for 180Nm.....

Or you stay 2stage and swap your final reduction. Like for a single 32T on the back, stock 12T front and no pedals. This would be like a 168T single gear on the back, so you'd get 168Nm of torque@the wheel doing 30 controller amps. BUT the belt is still an issue. Try it and we'll see, but always keep in mind it CAN break. I REALLY dont want any dead forum members! OK I agree on going for 32T on the back, but you will only be able to use the pedals on technical passages, on faster passages your gear will be too is too fast for pedaling. You might gear up then but you can still not pedal since it's too fast. Your drive just isn't geared right for this. If you WOULD want to pedal you should have gone for these rules: http://endless-sphere.com/w/index.php/Gearing_a_mid_motor

Denisesewa said:

Finaly got me kit today, Installed the motor and started working on the chain guide, kinda cool that one of the holes in the BB sheet was in a good enough place and the perfect size to accept a chainring bolt.

I drilled and tapped a hole for the second bolt.
Everything lined up nicely. I also built the battery tray but cant go much further on that untill the batteries get here ( still at least a week out), mounted the rear fender and fabed up a mount for the front fender, lots of work left to get them looking good so I'll stay busy.

Since I have had time while waiting for stuff to arrive I have been mocking up a battery cover which would be made out of carbon fiber but I'm not sure I like it, seems like it makes it look like a scooter or something , maybe I'll go with my original idea for just a battery box within the triangle, I can always add a cover later.

A little bit of progress eh?

Click to expand...

I really like the cover! It does not look like a scooter to me, looks like a mini Trials motor bike! just put some shapes into it to make it less "boxy" and you'd have it!

I decided to go a different route and started the molding process this morning, so it will have a carbon fiber "cap" on both sides and aluminum side panels for the triangle of the battery box. the top tube will be half exposed.


More pics after the epoxy cures and the pieces are trimmed.

I cant believe that its taken hobbyking USA warehouse 10 days just to get my batteries shipped, looks like another week before they get here

So this is what its going to look like although the fender and Faux gas tank will be nice shiny carbon weave when its done
The battery box framed up -



The battery box sheeted



And with the top on with black trim around the edges







So what do you think ? go with this? suggestions ?

I am worried that once its up and running I'll be known aroud town as a " Pedatrial "

Denisesewa said:

I am worried that once its up and running I'll be known aroud town as a " Pedatrial "

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LOL@ Pedatrial

Subscribed, nice project loving the custom fiberglass work

KiM

I like the look! You should build a seat that looks more like a moto trials bike that still fits the seat tube! That would be the icing on the cake! How many AH can you get in there?

Hi Denise,

Look's perfect to me, good work

Black Arrow

Whiplash said:

I like the look! You should build a seat that looks more like a moto trials bike that still fits the seat tube! That would be the icing on the cake! How many AH can you get in there?

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I agree with you , I've mocked up several seat ideas but here is the problem ,I still want to be able to raise the seat so I can ride it normaly , in order to get any kind of decent look to the seat I'd have to cut down the seat tube and its just long enough now to get to a comfortable height ( still not really high enough) so the only way I can think of is to build a telescopic seat post, that in itself poses several problems, the concept seems easy enough but actualy getting it built not so much.
I have been trying to do this build without damaging the frame and so far I've only had to drill and tap 2 5mm holes, anyway I'm still thinking about other ways to do the seat and I am open to suggestions.
The battery box will fit 14 s 2p turnigy 5000 mah batteries so I'll have 10 AH on board, The wiring and controller take up the rest of the space, once I get the batteries I'll see if there is any way to go 14s 3p but I doubt it, I want a clean look with nothing exposed.

BlackArrow said:

Hi Denise,

Look's perfect to me, good work

Black Arrow

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Thanks !!

Denisesewa said:

Whiplash said:

I like the look! You should build a seat that looks more like a moto trials bike that still fits the seat tube! That would be the icing on the cake! How many AH can you get in there?

Click to expand...

I agree with you , I've mocked up several seat ideas but here is the problem ,I still want to be able to raise the seat so I can ride it normaly , in order to get any kind of decent look to the seat I'd have to cut down the seat tube and its just long enough now to get to a comfortable height ( still not really high enough) so the only way I can think of is to build a telescopic seat post, that in itself poses several problems, the concept seems easy enough but actualy getting it built not so much.
I have been trying to do this build without damaging the frame and so far I've only had to drill and tap 2 5mm holes, anyway I'm still thinking about other ways to do the seat and I am open to suggestions.
The battery box will fit 14 s 2p turnigy 5000 mah batteries so I'll have 10 AH on board, The wiring and controller take up the rest of the space, once I get the batteries I'll see if there is any way to go 14s 3p but I doubt it, I want a clean look with nothing exposed.

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maybe you could make something along these lines?

http://www.buttrest.co.uk

Ian

OOooofff !!! , Buttrest = Butt ugly in my book .

I'll get something done eventually, batteries are supposed arrive today so the seat is going on the back burner for now.

No gasgas Hah! I love it! That looks like a total blast!

grindz145 said:

No gasgas Hah! I love it! That looks like a total blast!

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All I need to do now is find someone with some graphics skills to design a cool " No GAS GAS " graphics to fit in the triangle, Anyone ?

The GNG has a really nice motor that we should find a source of. I'm ridng trials stuff a lot those days and the GNG is prooving to be a really nice plateform do do so, I had my bike stuck with the motor on a rock multiples times without damage.

[youtube]IKw_FpR6jc8[/youtube]

I just got the duro leopard 24x3" tire for my rear wheel 8)