Twin motored PK Ripper--A little over the top!

Ok, Ok, Ok, I have been holding out for long enough. I really wanted to wait untill the bike was finished before I revealed it. But, what the hey, here are some "Not quite finished" pics.

The frame is a 2007 PK Ripper Team.
Fork is an aluminum, Echo trials item (very lite and super strong).
Cranks are Echo FW cranks with a White Industries FW.
Front hub is a Hope mountain bike item (36 spoke).
Rear hub is an extremely exotic (read expensive) Tri-All trails hub (also 36 spoke).
Front rim is 34mm wide double wall Sun brand.
Rear rim is a Nimbus aluminum double walled 44 mm wide unicycle rim.
Tires are Nimbus unicycle 110psi tires (1.9inch front 2.1inch rear).
Brakes are Hope Hydraulic 4 piston, floating rotor (160mm rear, 183mm front).

The bike was built from scratch as an EV.

I wanted to make the bike as close to an electric only vehicle without losing "Any" pedalling capability. I love to pedal. So, the pedals are not only for looks. The bike pedals just fine, no drag.

It will be geared (innitially) for 35 to 40mph. I want huge power and accelleration. Top speed is not really a concern.

I made sure the bike is built as strong as possible. Oh, I am also looking at several suspension fork options. If I go that route, I will also suspend the seat for a smoother ride. But, for now, I want to get it running.

The entire drive is overbuilt as much as possible for durability. There are 3 White Industries freewheels to allow the motor to run with or without pedalling without any drag or interferance between the pedals and the E-drive.

The rear sprockets are setup by using a White Industries 22 tooth freewheel drilled 12 times to be screwed to an aluminunm adaptor I made that, in turn, I have a 54 tooth, 94mm BCD chainring mounted to. This was a friggin pain in the neck to do. But, in the end, it turned out fantastic!

The rear end of the bike is pretty much taken to the limit. I cannot fit any wide rim or tire in the frame. I cannot run wider chains without interferance (BMX chains are fine). I had to widen the rear triangle/dropout area to fit the 116mm wide hub into the 110mm wide frame. It fits fine and the dropouts are still parrallel.

The battery is a 12S, 4P Lipo with a 9AH total capacity. Those are 20C cells. So, they should be up to the task of 10kw bursts.

I am hoping for about 47 pounds AUW. That will give me a shade over 3pounds per horsepower. This bike will have roughly 3 times the power to weight ratio of a two stroke motorcross bike!

So, who's got some questions?

Matt

Hehe, that's cute, Matt

I love the way the 2 chains are "mirrored"..

Awsome chain setup !!!
...and bike!
But I like those chains.

50cc counterpart... sort of





Just kidding!

OK - questions.

- Thumb throttle, I presume?
- Capacitance (details, please!) for the 2x HV 110s?
- Battery mounting intentions?
- Would you be offended if we set up a PayPal pool to get you a tripod??

Thumb throttle. Yup.

Capacitance. Six 1,000mf caps.

Batteries. In the frame triangle and in front of the rear wheel.

Tripod. Sure. :wink:

Matt

Very nice matt,
I am very interested to see how well it performs. Defo NOT over the top, do you think with the gearing that you are working with the bike would loop from a standing start i.e not move forward at all but pivot on the rear wheel. Im having major problems with the little setup im playing with ( its geared down a lot less but it is only a 2.4kw motor ) its crushing my output shaft bearings on the initial reduction stage!! they are very small so I think I will have to have a re-think . If I thought I could get away with having a fixed gear on the rear wheel ( that will easily loop the bike ) with say a top speed of 15-20mph then I can have a re-think on how the gearing is done and put nearly all the force straight on to the rear hub.

wow
thats going to do pretty nice wheelies !!!

gwhy! said:

Very nice matt,
I am very interested to see how well it performs. Defo NOT over the top, do you think with the gearing that you are working with the bike would loop from a standing start i.e not move forward at all but pivot on the rear wheel. Im having major problems with the little setup im playing with ( its geared down a lot less but it is only a 2.4kw motor ) its crushing my output shaft bearings on the initial reduction stage!! they are very small so I think I will have to have a re-think . If I thought I could get away with having a fixed gear on the rear wheel ( that will easily loop the bike ) with say a top speed of 15-20mph then I can have a re-think on how the gearing is done and put nearly all the force straight on to the rear hub.

Click to expand...

I know it would flip off the line. No question at all.

The bearings are 1/2 inch ID 1 and 1/8 inch OD. I may install an outer bearing support on the FW output shaft. That may be needed. I wil also install a strut from the drive to the bottom bracket just in case the frame mount clamps are not strong enough to keep the drive from scooting on the frame.

Oh, did you notice the drive clamps are machined in teh same oval profile as the frame tube? Another pain in the neck to machine!

Matt

recumpence said:

Oh, did you notice the drive clamps are machined in teh same oval profile as the frame tube? Another pain in the neck to machine!

Matt

Click to expand...

Yes I did notice and I think nessessary from some of the problems I have been having with the clamps moving around . The mounts need to be sound and solid. Looking forward to seeing it wired and running

Make me some too?
I don't want your drive to be a paperweight on my desk any more

Very very nice. I love how this one is turning out. Completely insane.

F-Yeah! freakin sweet bmx Matt!!
That is a great frame, pk ripper has always been one of the top bmx frames I know of even when I rode bmx back in the eighties.
I'm totally excited to see how this turns out, I just bought a bmx bike not 2 weeks ago and have plans to make it electric.
Im planning a slightly simpler build though as I dont have a shop just a hand saw and a drill press.
I got a specialized fuse 1 bmx, its way over built as its more of a freestyle bike, but it has stock a rear hub with threads on the left for left side drive setups
Im going to attempt 1 stage from motor to wheel.
Oh yeah, I'm about halfway done with my thumb throttle also
party on bmx bro 8)

Whoa....! the bike and drive system look really nice Matt.
8) and

Those tires look like they have some grip. It looks like a crazy
e-enduro sport-bike hyrbid.

It will never work.

Let me know how those batteries work. They are my most popular packs, and I use them in a ton of my RCs.

Awesome bike! She is going to be a handful!

I'm very excited to see how it runs

WOW, looks great!

I thought we were going to have to hold out quite a while to even get a peak at the bike 8)

Any chance we can get a close up of the rear wheel from the disk side? I'd like to see that caliper mount and the motor's rear sprocket from the back.

Looking forward to maiden voyage video footage! :lol:

I definately want to see circle burnouts if not stand up curb hopping wheelies! :wink:

One question: What is the reasoning behind the rear brake mount location? It seems a little exposed to curbs and other objects.

Man, you should be getting those freewheels at a discounted price as many as you have. 8) But seriously, I have been looking at all the expensive BMX bikes for sale and none of them even have the White freewheel, and now you go and put disc brakes on one, never seen that either. Sicko !

Really nice work

Show up with the bike and drive at one of those indoor BMX bike races and you'll have a mob scene trying to get a look at the bike. You could single handily start a whole new class of BMX racing. Well if the stuffy old folks don't get in the way.

Mark

recumpence said:

Oh, did you notice the drive clamps are machined in teh same oval profile as the frame tube? Another pain in the neck to machine!

Matt

Click to expand...

Very nice attention to detail! How did you measure the tubing? I could see using a contour gauge, taking a picture of it, and importing that picture into CAD.

Ahh, someone finally asked about the disc brake mount!

Yes, it is exposed there. The reasoning behind its location below the dropout is because of the slotted BMX dropouts. If the caliper were on top, the braking force would tend to push the rear wheel backward moving the wheel in the dropout slots. There is an axle stop bolt for chain tensioning that keeps the wheel from moving forward in the slots. So, mounting the caliper under the dropout puts the braking stress on that adjustment bolt, therefore eliminating wheel slip under braking.

I will try to get a rear wheel pic for you. I have one or two, but they are not high rez. :?

Paul,

I measured the tubing from the top and sides. Then I split the shape into sections and programmed it in G-code. Then I test cut a sacrificial part to varify its shape.

Matt

recumpence said:

Paul,

I measured the tubing from the top and sides. Then I split the shape into sections and programmed it in G-code. Then I test cut a sacrificial part to varify its shape.

Matt

Click to expand...

Is G-code limited to constant radius curves? I seem to remember that from my high school machining days.

Not really. There are exotic commands that add an algarythm (spelling?) to each successive line of code, whereby making and increasing or decreasing radius. Those are batch files, though, normally included in certain G-code softwares and/or in the mill driver/compiler.

I never learned that, however, because I have never had a use for it. Honestly, the tubing on this bike is sort of two .5 inch 180 degree radiuses connected by two .6 inch long straights. It is not quite as simple as that, but close.

Matt

Some electronic goodies to show, courtesy of JohnRobHolmes.

The packs are 25C. This 48 volt, 8.8AH pack is capable of puting out 10,500 watts. Perfect for my 10kw burst drive system. I will add more cells in an add-on pack for increased range when I want to go more than 10 miles or so.

Matt

Here are a couple more pics for you.

The rear wheel (sorry for the crappy pics. My hand is not too stable, nor the lighting very good).

I added a few pics of the drive unit (for those who haven't seen the other thread).

Matt

Wow, nice setup. Rethinking my next ebike conversion. Can you tell me more about the motors and where you got them.

Kin

They are made by Astro Flight. These motors are originally designed for very large scale RC airplanes.

They are listed at $400 each on their web site.

Matt