Project Phoenix

[Stollenritter]

I recently got hold of a pile of used MRC parts, and, having a look at my parts bin, it`s time to bring these parts back to life
This comes right in time as a christmas gift for a young lady

As this will be built (mostly) out of abandoned parts, I call it the "Phoenix"

So let`s have a look at what we got:





- two gearboxes with stock motor
- two axles
- lower and upper links (the hated Y-links)
- two not so good looking driveshafts
- four shocks (missing upper balljoints)
- chassis plates and body posts
- body (nearly full intact)
- stock servo
- battery tray

And that`s what`s laying around:





- set of slightly used wheels
- stock receiver
- stock esc
- HS-225BB servo
- Turnigy U-BEC
- LiPo low voltage alert
- another (new) stock motor
- 3Racing CVDs (as the Losi CVDs are discontinued )
- Spectrum radio (steering doesn`t work - we will see if it can be fixed)

This will be a fast build, never the less I plan on modding the suspension to a quick and easy four-link, as the body roll caused by the stock Y-link can be a pita.
Better steering will be achieved by using CVDs over the stock dog bones and the "mighty mini" Hitec servo, which, powered by the Turnigy BEC set on 5V can strip the M2 screws out of the stock plastic knuckles . The BEC can also set on 6V, but this would be to much until the knuckles and links are upgraded.

Next will be cleaning, disassembly, lots of grease ... you know the drill


Stollenritter

[Stollenritter]

Starting with examining the gearbox:



Everything looks nice inside, so: grease please



Next to the axles:



After disassembling and cleaning comes the first modification. I shorten the small noses on the knuckles, which act as a bump stock and limit steering angle.



For comparison, left side stock, right side modded:



And in action:



This mod is only usefull in combination with the CVDs. The stock dog bones won`t go any further regardless modded or not.

CDVs in place:





Next mod, preparation for the four link. Drilled and countersunk the servo plate:



This will be the attachment point for the new upper links.

[Stollenritter]

Started modding the chassis. Bent the upper chassis corners inward:



And attached the chassis plates back to the gearbox / skid plate:





Next are the upper links. The links are made from 3mm solid rod stainless steel.







I made some cross braces from 1,5mm aluminium sheet. The braces are fixed to the chassis with ball screws from the shocks.



I have to scrape some more rod ends together for the front axle now ...

[Stollenritter]

Next up are the shocks.



Cleaning and refilling with 27 wt shock oil.



Made a quick home brew outboard shock kit :



Looking nice so far:



And then - BAM! My wife found a "more suitable" christmas gift for the young lady
Ok, nothing wrong with that. That leaves me with a very nice set of MRC axles

I have the dim feeling this project will run into a comletely different direction now

Let`s see what we have: a chassis



A Subaru Brat body from my younger days of rc cars:



Set of SDi 1.9 Trail Docters:



Which look nice on the chassis ...



... and not even too bad with the body on





All in all not what it was ment to be, but hey, that could be a fun little rig!

[Stollenritter]

I recently had some time for the Mini, so I started to set something right. I allways hated the poor steering geometry of the MRCs. Due to negative Ackermann effect the outer wheel is turning further inward than the inner wheel. There are some zero-ackermann knuckles available, but that`s only half the battle.
This is how it looks stock:





To get a positive Ackermann effect, the easiest way is to draw a line from the pivot of the knuckles to the center of the straight / rear axle. The fixing points for the steering rod have to be on that line.

So I started a little sketch (dimensions in mm):



107mm is the width between the pivots of c-hub and knuckles of the front axle, 215mm is the MCR stock wheelbase and 245mm is the wheelbase for the Subaru.

I made some simple knuckles with interchangeable steering arms:



As the drilled holes for the bearings go straight through (for the ease of manufacturing), I had to use flanged bearings to prevent the CVDs popping out:



The outside bearing is a standard ball bearing:





Complete knuckle with steering arm on top. The knuckle is made from of simple stainless steel pieces welded together, the steering arm is made of aluminium. No perfect beauty, but easy to do without a lot of machinery:

[winnerone23]

Awesome work sir! Continue on and keep up with the Great pics!

[Stollenritter]

Front axle complete with positive ackermann steering and new steering rod:



Steering angles for comparison:
(new)


(new)


(stock)


A further benefit is the "behind the axle" steering rod, this will give some more clearance up front

[Stollenritter]

Originally Posted by winnerone23

Awesome work sir! Continue on and keep up with the Great pics!

Thank you, I will do so. Even if it will take some time.

[j0e]

Awesome work on that steering!

[Stollenritter]

Originally Posted by j0e

Awesome work on that steering!

Thank you!

If there is some interest, I could post a few more detailed pics and a little sketch so people can build their own "positive" ackermann knuckles. Just let me know.

[pauly383]

Digging those knuckles

[OTHGbronco82]

Originally Posted by Stollenritter

Thank you!

If there is some interest, I could post a few more detailed pics and a little sketch so people can build their own "positive" ackermann knuckles. Just let me know.

Hell, I'd take a sketch. Just have to make sure to include a Square for accuracy and scale. Like a 1in x 1in or a 10mm x 10mm.

[Stollenritter]

Originally Posted by pauly383

Digging those knuckles

Thank you!

Originally Posted by OTHGbronco82

Hell, I'd take a sketch. Just have to make sure to include a Square for accuracy and scale. Like a 1in x 1in or a 10mm x 10mm.

You`re welcome. Good idea on the square for scale, I will take care of that. I will redo my sketches and add a sectional drawing to show all the dirty details

[OTHGbronco82]

Originally Posted by Stollenritter

You`re welcome. Good idea on the square for scale, I will take care of that. I will redo my sketches and add a sectional drawing to show all the dirty details

Cool. I should be able to draw them up in Auto CAD and have a pair machined as I don't have any brazing or welding stuff. I could always use a little more steering on my MRC though.

[Stollenritter]

Originally Posted by OTHGbronco82

Cool. I should be able to draw them up in Auto CAD and have a pair machined as I don't have any brazing or welding stuff. I could always use a little more steering on my MRC though.

Please keep in mind, to gather more steering angle you have to put in some CVDs. As the Losi CVDs are not longer available, I bought some 3Racing CVDs for mine.

I got some time to do start with the drawings. The first one will show the difference between the stock knuckles and the selfmade knuckles. To simplify manufacturing, I replaced the welding joint by a bolted connection. This cannot be seen in the first picture due to the sectional representation, but we will take care about this later.

The upper one is stock, the lower one is modified:



The next big difference is also justified by the ease of manufacturing. The stock knuckles have the seatings for the ball bearings done from either side, so there is a small "truss" left in the middle. So the bearings have to be put in from each side. This is neccessary to prevent the shaft from moving out of the axle housing. As I haven`t been able to mill the seatings from different sides, a have a straight through hole through my knuckles. To prevent the shaft from moving out, I used a flanged bearing on the inner side, which can be seen in the lower picture. To take care of the thickness of the flange, I had to offset the distance for the kingpins to align the kingpins with the center of rotation of the CVDs.
This is just for explanation, all these calculations will be respected in the later drawings.
The attentive observer will have noticed the small green spacer between the ball bearings in the lower picture. This is a small ring made of paper-clip wire (0.6mm diameter). This spacer is a must to prevent the bearings to be jammed togeher.
As some of you will use 3Racing CVDs, they have a little bug. The aluminium sleeve is to long and will also jam the bearings. The aluminium sleeve has to be shortened by just about 0.5mm. I have done this by simply shaving it on a piece of sanding paper. In the picture above the sleeves are shortened.

So this is a lot of information and I hope I haven`t butchered it up with my poor language skills.
For any questions, feel free to ask.

[OTHGbronco82]

I have CVD's so that isn't an issue. It all looks good. Can't wait to get some measurements and make some of my own.

[Stollenritter]

So, first part is the center piece of the knuckle. This one can be made of steel, brass or aluminium, whatever you have at hand or prefer to work with. Mine are made of steel, as I wanted to weld them to the lower brackets. Steel will add about 2.9 times more weight to your axle as aluminium. Brass will be 3.1 times heavier than aluminium.



Dimensions are in mm, projections of sideviews are "metric", which is opposing referred to the imperial projection method (which in fact is irrelevant for this part, as it is symetrical in two axis).

[OTHGbronco82]

Finally got my computer up and running again. I'll see what I can come up with in auto cad so I can have them machined in brass.

[Stollenritter]

Originally Posted by OTHGbronco82

Finally got my computer up and running again. I'll see what I can come up with in auto cad so I can have them machined in brass.

Weight in brass should be 7,8g. You can add some more weight if you enlarge the width from 12mm up to 15mm. It could be looking like this:



This would have a weight of 10,4g. A nice kind of knuckleweight

[winnerone23]

Love the design! Couldn't a larger bearing be put into place with this as well?