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

[Honza 704]

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.

 

[Honza 704]

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?

[cstorckiii 153]

53301-TL01 Suspension Shaft Set.

[Honza 704]

@cstorckiii Thanks, unfortunately that's a 3mm shaft, I need 2.6mm for the XV-02 hubs.

[cstorckiii 153]

Ream out the hole in the hub?

 

[Honza 704]

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

[Honza 704]

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:

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

[Honza 704]

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.. 

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

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.

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

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.

[Honza 704]

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.

[Aerobert 1975]

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.

[Honza 704]

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. 

[Aerobert 1975]

 

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. 

[Honza 704]

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.. 😀

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.

 

[Honza 704]

(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.

[Honza 704]

Disassembly didn't happen yet, I'm preparing some replacement parts... 😉

[Honza 704]

V2 prototype is nearly finished

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

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.

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