UniRacer

The forward motor rotation will cause pitch-up under power, as commented above. There is also a Gyro-rotational effect that causes additional lateral weight transfer in the corners. However Tamiya designed their latest M-07 and M-08 cars like that as well.

Also I'm wondering about the forward placement of the steering servo. I'm unsure if it will give the correct ackerman geometry for the steering linkage. I was suspicious it may cause toe-in when steering is added.

wtcc

iTrader: (2)

Thanks guys!
I guess the motor rotation is not optimal and will add to the effect of tires, diff and cvs. Right now I like this simple gearbox design too much to add another pinion to it. It is definitly possible with little changes to the gearboxbulkheads, a turn of 180 degrees for the shocktower and motor, a position switch of motor mount and that arch on the other side. Sounds a lot, but only would need new gearboxbulkheads. Sensitized like this I will take a close eye on this topic on the first runs. Thanks for bringing it up

@UniRacer: We had that Ackermann discussion earlier here. I did practise days with different Ackermann settings and found that a slightly wrong Ackermann angle suits the car much better and reflects positive on laptimes.






I printed the rest of the chassis parts and did a provisional assembly. I am glad I did it! I found two mistakes and some improvements. Mistake number one, was a wrong hole distance for the rear armmounts. I needed to increase the distance to fit the arms in between and have the possibility to reduce or increas the wheelbase. The second mistake was another wrong hole distance. This time the servoarm plate needed to be corrected by 0.5mm.
The improvements involve a closer position of the rear dampers to the middle axle, added cut outs for more free movement regarding the active toe links, a new form for the front anti-roll-bar to avoid a collision with the inverted steering arm and a stiffer rear end design for the topdeck.

The rest of the "build" went on without problems. It looks like it could drive already. It would, but having super flex

Eotz

What material have you used for printing the gearboxes?

CTE

wtcc That looks awesome! Just realised you are running a 2 gear transmission. That is super interesting to me given i am trying to design a 4 gear for my FF03. Maybe i can make a 2 gear work and reduce height, weight and drag.

If you end up needing a 3 gear, i would worry too much. All you need is 2mm clearance between the diff and crown gears and add an extension to your bulkheads above them to fit a 27t tamiya idler. You would change much on the layout.

wtcc

iTrader: (2)

It is just simple plain PLA. I think it would be tough enough for the normal use, but in the end I always order sintered parts.

UniRacer

I looked back and found the discussion on the previous pages. Negative ackerman should normally cause a lot of understeer. Some possible reasons why it works:
1) If your diff setting is close to being locked, the Ackerman may not make as much difference.
2) Perhaps there is some bump-steer that causes toe-out when the front suspension compresses. That could be compensating for the negative Akerman. That type of bump-steer may also have some effect to stabilise the car's response, and change the way the car responds to spring rate and sway-bar settings.

BJS414

This is a lot nicer gearbox/motor layout than the current fwd trend (just 4wd with removed rear belt is all what professional RC designers can come up with?) that have the motor and battery way out to the sides.

CTE

wtcc What size spur and layshaft gear are you using? What FDR are you planning to run? I tried laying out a 2 gear transmission for my FF03 last night and it was hellish difficult! Ended up needing the 24t layshaft gear from a TA06 to move the shaft far enough away from the axle to clear a reasonable sized spur and still get a couple of decent gearing options.

wtcc

iTrader: (2)

I know the horror you are talking about.

The geardiff has 52 teeth (48dp) the counter gear is 20 theeth. That will come down to 2.6 internal ratio. My spur is 80 teeth (64dp) and my pinion 46 teeth. Like that I come to 4.52. With a 41 teeth pinion I get 5.07 ratio. The shortest I can do is 5.33 (39 pinion). I got space for a slightly larger spur, maybe 84 teeth, but never tried. And of course I can go lower than 4.5 with larger pinions and smaller spurs, but also never tried as I optimized the car for ETS and Tonisport Onroad Series.

What I found important while doing the gearbox layout, was to rise the differential to 19mm above the chassis plate (to center diff). That way you not only reach optimal cvd angles, but also avoid collisions with other parts. The spur should sit just several millimeters above the suspension arm. The spur gear shaft with counter gear sits 27.25mm above the chassis plate and 17.71 millimeters behind the gear diff (measurement is center to center).

I hope that helps.

CTE

That is SUPER helpful. Thank you. I think diff height is the key. It's only 16.5 above the deck on the FF03, and i thought keeping the diff low would be good.
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Bry195

When the car goes from 1 gear to the next does it disrupt anything in the car? For example the transition isnt smooth or there is a delay?

normally you calculate the average speed required to run a lap in at a lap time. When running 2 gears do you use one gear for infield and one for outfield or ...average corner speed versus average straights speed? It seems like 2 gears become an expertise in RMS temperature. Over driving one gear but getting your temperature under control with the other. 100% duty cycle on the motor but one gear at 150 and the other at 50.

wtcc

iTrader: (2)

Good joke pal!

Nerobro

iTrader: (2)

Negative ackerman is a thing in real racing too. As you reduce load on a tire, I understand that rubber tolerates less slip angle. By reducing ackerman, in the lightly loaded tire, you can get more overall traction.

UniRacer

I don't know too much really clear data, especially not for 1/10 scale tires without air pressure. Graphs I have seen in the past for REAL pneumatic tires at low normal-force loading, show generally mild and progressive break-away characteristics. I would not only look at the tire slip-angle to achieve peak cornering grip. For the case of the inside tire with reduced loading, I would look at the maximum tolerable slip-angle before the grip falls away. There may also be areas in the tire performance envelope between zero load and maximum load that perform as you say. I am not totally disagreeing with your point, but there is more than one way to look at the curves.

There is also a dynamic situation for cornering stability. With the negative Ackerman, it can make the car less stable in the mid-corner situation. As the weight transfers to the outside tire, negative Ackerman will cause the car to take a tighter line. It will force to the outside tire to load-up even more. That instability is likely to create an overloaded situation where both front tires loose traction. Generally smooth cornering and slow weight transfer is the best recipe for good grip - I think real racers know that lesson very well.

Apologies to wtcc if this discussion is off-topic. Its great that wtcc did his own testing to find some answers that work with his specific car.

wtcc

iTrader: (2)

The discussion is welcome
It helps to develop new ideas and overcome problems.
Sometimes I am „blind“ and do not see design flaws, but you guys see them and help the project to grow in a good way


As we talk about it...
Right after printing the chassis and doing the provisional assembly, I recognized the space behind the motor can. After doing experiments with the gearing, I verified, that I wasted space here. One goal with this car is to group all heavy components for more agility. So right after the "design freeze" it became time to redesign some parts



I deleted the wasted space and redesigned that central bulkhead to allow the battery to sit 11mm closer to the motor. All electronics behind will move with it. The right mounting was relocated, because on this side are the motorconnectors. Then I thought about the shocks. These could sit on the central bulkhead, too. Loooooong pushrods will connect them with the rocker arms. The cable tunnel needed a new design also.





And for more fun without tape on the racetrack, a new battery brace was drawn. It can rotate around its mounting on the central bulkhead and has a mount in front of the esc.

The more I design, the more I am looking forward seeing this car run for the first time