Open Class: drbhuntnfish 2x2 hydrostatic minibaja

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drbhuntnfish

New Member
#1
#1
My entry for the 2013 OldMiniBikes open class is an attempt at turning a minibaja MB165 into a 2x2




This has been an idea I've had for several years. Several years ago, I bought two MB165's...



One of which I modified by adding a rear rack, a mesquite tree shield (windscreen), and a platform where the fake tank mounts. I've used this one for several seasons for packing me, a shotgun, a dog, a blind, and a blind-bag into the woods. This is an early pic from the first season...



This is the current rendition of this bike with a TAV added...



Now I'd like to modify the second bike to be a 2x2, sort of a mini-rokon type affair, except I want to have this be a hydrostatic bike. The plan is to use a variable displacement piston pump along with two fixed displacement motors plumbed in series, one mounted on a truss across the front forks, and the other mounted near the rear tire. Each motor will use chain to drive the wheel sprockets.

Here goes...!
 
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drbhuntnfish

New Member
#8
#8
The Raccoon bike is indeed the inspiration for my build. There is a wealth of information about the raccoon and other hydraulic machines available on the Hydraulic Innovations forum.
The main difference between my build and the raccoon is that the raccoon does not use chains or sprockets, and the bike is purpose built. Since my build is an adaptation, it will use chains and sprockets, because it will allow much smaller hydraulic motors (less weight), and more adjustment in gearing, and since I haven't done anything like this before! :shrug:
 
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drbhuntnfish

New Member
#10
#10
ICE, hydraulic pump, and hydraulic motors

I stepped out into the shed just long enough to take a picture of the planned powertrain for my 2x2 hydrostatic minibike project:



This shot shows the 196cc internal combustion engine (ice), the 1.1 cu. in. variable displacement piston pump, and the two, 2.5 cu. in. hydraulic motors that I will use.

There are several interesting characteristics of this setup used in a 2x2 application, I have learned.

1) The pump has a swash plate that increases or decreases the pump internal volume. If the swash plate is at zero degrees (nuetral), no fluid will flow, and the bike won't move. If the swash plate is moved one way, the flow is such that the bike moves forward. If the swash plate is rotated the other way, the bike moves in reverse!

2) Since the swash plate moves smoothly from zero displacement to 1.1 cu. in. displacement, the pump is like a continuously variable transmission. Infinite gearing between zero and 1.1 is possible. I will talk more about the overall gearing I chose later on in the build.


3) The ICE throttle is independent of the swashplate position. That implies that one could run the engine at its peak torque setting, and use the swash plate to control the forward and rearward speed of the bike. You could for instance run the ICE at full throttle, and barely crack open the swashplate, and have a tremendous amount of torque available to you, albeit at very slow forward or rearward bike speed.

4) The 'hydrostatic' term implies that the system is closed loop. Simply put, for this project, with the motors plumbed in series, hydraulic fluid runs from the piston pump to rear wheel motor to the front wheel motor and then back to the pump. There is a reservoir required, but it is not connected in this loop.

5) The motors will be plumbed in series which automatically provides a posi-trac effect between the front and rear wheels; whichever wheel sees the most load receives the most power from the hydraulic fluid. For instance, if the rear wheel is on ice, and the front wheel is on pavement, the pressure drop across the rear motor is much lower than across the front motor, and the power goes to the front wheel automatically.

Edited because I forgot one important point...

6) Because the ICE/pump is connected to the motors by hydraulic hoses, it doesn't really matter what the ICE driveshaft orientation is relative to the plane of the rear sprocket. The driveshaft could point to the rear, left, right, forward, or any orientation in-between. A V-twin with a rear pointed driveshaft is no problem, for instance.

End edit...

The one thing I really have to watch is the weight of the bike. Each motor weighs 15 lbs, and the pump is about 10 lbs, iirc... The added weight will probably be on the order of 60 lbs. However, all is not lost, as I will show in my torque calculations to come...

Cheers!
 
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RobertC

RobertC

#14
#14
Hey drbhuntnfish,

This is going to be great !

I continue to be impressed daily with the depth of knowledge, and experience, from the folks here at OldMiniBikes.
 
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drbhuntnfish

New Member
#15
#15
Trial mounting the front sprocket and hydraulic pump

Hey friends,

I don't have a great deal of progress to report, but worked on two things this past week - getting the front wheel mounted with the sprocket on it, and mounting the pump to the ICE, and checking for clearance on both.

For the front wheel, I bought a slightly used rear wheel assembly with the brake and sprocket attached, and mounted it in the front forks. I want all the chains (rear wheel, front wheel, and pump) to be on the same side of the bike for now. So that forces the brake to be on the RHS with the lever forward - a tradeoff. Also, I am trying to go with the least amount of mods possible to the bike, so the front tire will not be in the center of the forks (no fork mods) - you can see in this photo that with the sprocket on the bike, the wheel is offset to the right a small amount. I had to have a thin aluminum spacer fab'd to get everything to fit:



This picture shows the front sprocket with the chain draped over it to check clearances. The aluminum split-clamp that is on the front fork was obtained from McMaster-Carr - I'll be using four of these to mount the hydraulic motor to the lower forks via a aluminum bridge mount (to be fab'd). The split clamp has about 3/32" clearance between it and the sprocket. So far, so good...



The first mod to the frame was to remove the jackshaft tab on the ICE mount. It was easy to remove after using a hacksaw to saw vertically through the tab down to the mounting plate. Then I took some vice grips and broke each tab half off separately, then cleaned this edge up with a file...



Now for the fun part - the overall implementation plan is to use as many commercial-off the shelf parts as possible to make this build easy for anyone else to duplicate if they want... Sometimes this works out great... I lucked out in the area of the pump mounting plate - I modified a Comet TAV2 aluminum mounting plate (BMI karts) by having the driven support milled off flat, and also machining a hole for the pump to fit onto the mounting plate. Then I mounted the plate to the ICE. The hydraulic pump mounts directly over the ICE, and luckily, the whole thing mounts into the frame of the minibaja...



Here's another shot of the assembled power pack from the RHS...




The TAV2 plate isn't thick enough for me to feel comfortable with cantilevering the pump over the motor like it is shown, so I used some .10 galvanized metal to make a bracket to tie the pump to the ICE. I made a template from cardboard...



...fitted it to the pump and ICE...



and then cut it out using a throatless shear (Woodward Fab) to cut out the bracket, and a bench vise and a plastic hammer to bend it. I tried to keep the bends gentle to avoid any stress risers. Here's the bracket in place...



Next, is to figure out how to mount the front hydraulic motor to the forks.
This is a work in progress (I plan to use four split clamps, not just the two shown below). I'll be using 3/8" alum to make the bridge mount. Hopefully something like this will work...




'Til next time! Thanks everyone for all the great comments. I am watching all the great builds in the buid-off - what a blast!

Cheers!
drb
 
Stangrcr1

Stangrcr1

New Member
#16
#16
Nice work!

One question. How will you tension the belt from the motor to the pump? Idler?

1/4" plate would probably suffice....

Also, you could build it where the top was level and use the bracket as the front fender too..
 
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N8ball

Member
#17
#17
This is very interesting. The hydraulic 2x2 is going to be unstoppable. I have wanted a Rokon since I was little. It's cool you are building your own version. I am going to have to check out the Raccoon to see the source of your inspiration.
 
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