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MF-01M - A mid motor 4WD rally M-chassis

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Prototype of the entire axle is done. I used XV02 caster blocks, as they have some improvements over the XV01 ones. Also had to move the inner top link mount down for proper camber change.

The arm is really just slightly modified rear arm (although it'll need more modifications to fully clear the rim). The damper mount is now closer to the inner axle relative to length of the arm, so the damper feels much softer.

 

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Welp.. back to the drawing board.

While the suspension seemed to work quite well, The arms didn't like direct hits from cobblestone track on this weekends race. Both arms failed after couple of meters. Looking at the state of the rear arm, I'm not surprised. At least the rear suspension mounts appear to be strong enough to withstand direct blow.

Btw, anyone knows about a 2.6mm hinge pin with grooves for E-clips?

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On 7/14/2023 at 3:40 PM, cstorckiii said:

Ream out the hole in the hub?

 

That's something I wanted to avoid - weaker material, potential inaccuracies - but there might be no other choice

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Ok, so I reprinted the whole front suspension just to scrap it and start again. The reason is movement of the driveshaft, which would require some longer differential outdrives, which would require custom manufacture... something I don't want to do (yet)

So back to stock front end. It seems, that reason why it doesn't work, is lack of any leverage between the arm and damper - the damper is nearly at the pivot point. It somewhat works with stock dampers thanks to their angle, but the longer shock I use, cannot be laid down as much.

So I decided to replicate the original arm, but with damper pivot moved inwards by similar amount to the rear suspension. This somewhat worked to make the suspension softer, bit it also raised the pivot point of the damper, resulting in very non-linear characteristics.

To address this issue, I designed the Bananarm:

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The curved shape moved the damper mount some 4mm lower. First test shows that it could work, but it needs some adjustments.

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Today I printed V2 of the Bananarm. It looks like the V1, but I draw it from scratch. The damper ball was moved 1mm further to the center, moving it further lower while also allowing me to add some clearance around the damper eyelet. The center of the arm has more material and modified shape to clear the C-hub properly. Overall, the front is now much softer, with wider range of movement.

Unfortunately it's been raining all day, so I couldn't test drive it yet.. 

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From left to right - stock arm, stock arm, flat arm with relocated damper mount, Bananarm V1, Bananarm V2

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Reason for the bananarm name. The curve have no adverse effect on the ground clearance and hopefuly minimal effect on rigidity, but big effect on suspension stiffness and linearity.

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Mounted on the chassis. Ground clearance is now limited by the driveshafts.

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Same limitation at the lowest point. The dampers could go lower, but the driveshaft mashes into the diff cup. It's still improvement over the stock.

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Results of the test drive. It took a few direct hots. I think it's better when the printed parts are ones that fail. I'll try to get my hands on the 53301 set, to strengthen it a bit.

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On 7/3/2023 at 8:49 AM, Honza said:

Btw, anyone knows about a 2.6mm hinge pin with grooves for E-clips?

What length do you need? There are some for the F103GT with a length of 35 mm.

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56 minutes ago, Aerobert said:

What length do you need? There are some for the F103GT with a length of 35 mm.

Thanks, I need something around 28mm. Longer shaft won't fit inside the wheel. 

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12 hours ago, Honza said:

Thanks, I need something around 28mm. Longer shaft won't fit inside the wheel. 

Unfortunately the F103GT ones are 35 mm. If I see something suitable I will let you know. 

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After summer break, I could finally take the car to a race. The front suspension finally worked! Well, it wasn't as stiff and actually lead the front. Here's video I made, hoping that it'll help me to tune it further.. it won't, but I think it's a nice shot anyway :)

Btw, I reprinted the arms out of softer PETG. They survived the race, but the bashing afterwards.. well.. 😀

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Btw, I also got a tip how to make my own 2.6mm shafts with e-clip grooves. So I might revisit the long span suspension concept.

 

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(Photo from a fellow racer)

Last Saturday, the car finished the last race of the season

Although it competed only in 5 races out of 8, it still accumulated 21km - with just a single failure, which was loose pinion gear. I'm gonna disassemble and inspect whole chassis for wear.

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V2 prototype is nearly finished :)

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This version has several improvements:

- The most obvious is new vent over the motor. Its grill is a separate part that can be replaced with a fan to further improve cooling, which wasn't ideal on the V1.

- the motor mount is now mounted from the outside. That necessitated a separate gear cover, which improves serviceability of M-chassis gears. Speaking of motor, it's now fixed via stock screws, and other non-original screws were eliminated as well. Also, the design can also supports mount made of aluminium sheet, which is something I'd like to do in the future.

 

- motor is moved a few milimeters forward, which allowed me to add some material around gears, so they should be able to handle more power.

- suspension mount is now a separate part. That opens more options for setup and makes repairs easier.

- new design of suspension tower mounts. It supports layout from V1, but also M05 adjustable top links. Finally, I got rid of those weird extensions

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I still need to do some finishing touches, like drilling a new hole in the driveshaft, since rear bevel gear has been moved to the front - again. But the model itself went together well, maybe better than V1- after some adjustments, I may release it. 

Also, I played a bit with old rallyblock tires. So far, it looks promising.

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Unfortunately, winter has come here, so I won't be able to do any tests anytime soon.. well, time to work on another projects 🤫

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Nice work. Looking forward to see the results of these changes and improvements.

 

BTW is a rally car immensely fun on snow or hoar frost.

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2 hours ago, Andreas W said:

BTW is a rally car immensely fun on snow or hoar frost

Thanks! Well, the driving is fun, drying the car afterwards, not so much 😀 Although the receiver is in a box and ESC should be waterproof, I don't like driving in wet conditions.

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I finally had some time to work on the project. Today I printed parts that are pretty close to the release model. I also disassembled the current version to check internals.

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You can see some dost got in, but nothing too bad. The gears are worn a bit, but they'll work well for another season.

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Spur damage caused by loose pinion. I'll reuse it as well.

Now to the build of new parts.

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The new design is more optimised for printing, all bottom surfaces are bridges to reduce amount of support material. I'm quite happy with the finish, considering it won't be visible. 

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New gear holder, now fixed in three points around the gear - I could hear some gear skipping on the previous version, this solution should be stiffer.

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With differential, fan and the other gear in place, the gearbox can be closed now. 

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The diff case is clamped together by the suspension mount. I added M3 nuts, since I expect that this part will be changed quite often.

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The motor mount is now mounted from the outside. This makes maintenance easier, and opens possibilities for modifications, like aluminium motor mount. That's something I want to do in the future, but for now, ASA plastic will be good enough.

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And gear cover fitted.

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All went together with M3x10 screws only.

I found some snall issues during the assembly, that need to be fixed, but afterwards, I can finally release the model files :)

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Done! I'm happy to share the V.2 files :)

https://www.printables.com/model/712311-mf-01x-midship-motor-conversion-v2

I reverted to long top links and kit shocks to test the stock damper stay design. This is only temporary. What is not temporary is the small aluminium piece of wrong color 😀 Unfortunately I didn't find red or black 5mm hexes in my local shop (they are available now) and it will be hidden under the wheel anyway.

Edit: I also forgot that I finally got to modify the propshaft, so it's 4WD again! 😁

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That is PERFECT! 👍👍👌

Now, if only I could get my 3D Printer out of storage... and LEARN how to use it!! 😮🙄😪😭

.... Unless someone in the United States could print and ship me the parts. 🙏🙏🙏  I've got a MF-01X, DYING for a mid motor!

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Last few adjustments and I think that the car is ready for the next season. I just need to finish the other two DIY rally block tires and test if they stay in one piece 😁

Since I switched to a different RC unit with a more compact receiver, I could design a new chassis extension piece that could fit the receiver inside. It looks much better without all the wires running to the rear

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I'm still not happy with the front suspension. Custom "banana" curved arms with damper pivot moved closer to the inner hinge pin helped to get softer damper action, but also resulted in non-linear spring rate with long front dampers due to their more upright position. So I returned to old black Tamiya dampers, which could fit into original damper mounts, with YR piston shaft to gain 2mm of length. Thanks to custom arms, they have just enough active length to cover whole suspension travel.

(Picture that compares two types of damper didn't upload)

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I also designed a new bumper prototype, which should be stronger against hit from the bottom and act a bit as a skid plate. I also found a piece of black foam, which I thought would look better than the white foam I used before.

I'm thinking about getting TT-01 foam, which comes in variety of sizes and is 5mm thinner, which would gain some ride height.

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(Photo showing bottom of the bumper didn't upload)

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Once I finalise the design, it'll be printed out of the same black plastic as front arms, which has slightly better impact resistance than the red PETG.

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And photo of the complete chassis, before a little teaser - I went through parts left from the previous builds and realised, that I'm not that far from completing another MF-01X... Or should I say TL-02? 😁

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Btw, I also checked the weight - without the body, the car weights 1390g, with 48/52 F/R split. My target was slightly above 50% for the front axle, so it's not that far off.. and vast improvement over the stock :)

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This is a fantastic build. The engineering here is fantastic and I bet the car is transformed. 

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I finally finished something I wanted to do from the start, but didn't get to it: Suspension blocks which will hopefully work with M-05 V.2 arms ( I don't have them to test), but what's more important, with different toe-in. For the start, I did 0, +1 and -1 variants. I  installed the -1 variant and will test it tomorrow

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Hand since I have several replacements, I did crash test of the stock part. It worked as intended with crash from the front. But impact from the rear was a bit unpredictable and nearly torn away the chassis mounts. I will have to do some changes.

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Two weeks before first race of the season, Mazda's driver needed some practice. I tried to make some photos, but my phone couldn't keep up, so they are blurred from cropping and motion.

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