Kyosho PureTen Martins EP convertion to FWD

[Germano]

Hi Guys,

I'm from Brazil. I'm not good talking in english but I'll try to share with you my last project. It is about converting the Kyosho PureTen Mantis EP RWD to FWD.
Kyosho PureTen Mantis EP RWD was my first hobby grade rc car. I bought in 2006, I guess. I upgraded the chassis with parts from orthers cars.

That was my car:









Novak brushlees combo 3.5 10500kv (first brand to make a brushless sensored), hpi super star wheels/tires, hpi Pro4 shocks, carbon fiber shock towers (that was replaced by carbon fiber shock towers from Xray T2'007).
Unfortunately somebody stole my car in 2008. Wheels and bubble remained. Fortunately, I had another chassis mantis because it already was hard to find parts of that car in 2008.
When I saw EvolutionRevolution converting the same chassis to FWD, I decided to do that too.

So, here is my backup chassis:

I put some electronic to see how that car would be.

I'll install the following motor:


I'll try to run with foam tires in the rear. RWD slid too much, even in "off steering".



That hub is an optional part for Kyosho Optima e Javelin. that vintage cars was re-released in 2016. There isn't that optional in 1985, when those cars was released for the first time:






Left, standard diff gears, made with antimony. Right, the upgrade, made with steel. That upgrade is a standard part of Kyosho FW-04 and optional for Alpha 2.









Upgrade in the transmission. Cvd's for HPI RS4 Sport 3. Before, it was dogbone, even in FWD version.










Rear hub has bushes to set the toe. there are marks to inform the degrees.



I decided to replace stock suspension arms by Kyosho TF-2/TF-3 arms, hard version.



I had to sand a bit to fit the car. On the left, is the modified part:






Left, new suspension arm. Righ, stock suspension arm:



Now, right side with new suspesion arm too:








Front suspension arms was replaced too by Bv3 suspension arms:






I adapted those shock towers from Sakura XI Sport:


Shocks from HPI Rs4 Sport 3 Drift:


Rear finished:



Aluminum C-Hubs and turnbuckles, from Jazrider. Those are opcional part for Kyosho Javelin and Optima.


Front finished:






Replaced stock diff cups by a heavy duty version. It's made for HPI NItro 3:





New diff cups installed:



Now, chassis with servo installed:


Steering system is ready:


Esc Mamba Monster:



Receiver frysky for my futaba 4pk.



Battery zippy 2200mah 3s. It was the only battery that fitted.




Car is ready to run: 5900 kv motor, 3s, 31 tooth pinion and sorex tires.









After first run, I realized the rear sliding easily during the corners (RWD configuration has the same behavior). So, I put foam tires on the rear and that issue disappeared.





But there is another problem yet: dump steer

After talking to some members of this site, I'll install stock suspension to check that issue persists. As EvolutionRevolution said, the modifications should have changed the car geometry.

[Coelacanth]

Germano, although I don't have a Mantis, principles for reducing bump-steer would be the same for most cars. Looking at your pictures, it seems like the bump-steer could be improved:

There appears to be a lot of spacers where the outer tie rod ends bolt to the steering hubs. It looks like much of this extra space could be removed, and the tie rods would more closely match the angle of the front arms, even if you kept that rather large servo horn. I'd change that horn to a much shorter one though, as that would help to raise the inner tie rod ends and that would help reduce the bump-steer too.

I see the outer tie rod ends thread into a weird angled plastic piece and I'm wondering if it wouldn't be simpler to just install ball-studs in the steering knuckles and pop ball-ends directly onto the studs? Like these items, 4.8mm low profile ball studs and 4.8mm ball cups. I believe your tie rods are 3mm threads, and ball cups like these would screw right on, and do away with the weird angled ends. (Unless of course those are required to avoid some kind of obstruction, but I can't see that from the pictures...)

EDIT: I do see on the right side that, with the oversized servo horn you've chosen, the right tie rod might contact the blue gear gearbox cover...but with a shorter horn, you might still be able to raise the insides of the rods and also lower the outsides by removing some of those spacers, and get quite a bit closer to a parallel angle matching the arms.

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Capture2.JPG (24.71 KiB) Viewed 1442 times

[Germano]

Hi Coelacanth, thank for spending your time to help me

I bought the following servo saver:



I hope that decrease the angle of steering links.

It is complicate to lower the steering links. Left side doesn't have obstruction. Right side is necessary to take care with the link not hit the gear case.
Those aluminum knuckles have different design. With the stock steering knuckles, it isn't necessary the spacers.

[Coelacanth]

I'm not sure how much clearance you have between the body and the top of the steering servo, but could you also mount it a bit higher, i.e. raising the servo higher by drilling a few new mounting holes? Raising it a bit there might give you just the bit of angle you need to make the tie rod angle more parallel to the arms.

Another option, if the right side has more obstruction issues due to the gearbox...is flip the servo over so the shorter end relative to the servo gear is to the right instead of the left. Then just reverse the servo direction with the transmitter.

[Germano]

Another option, if the right side has more obstruction issues due to the gearbox...is flip the servo over so the shorter end relative to the servo gear is to the right instead of the left. Then just reverse the servo direction with the transmitter.

Servo horn would hit the spur cover
But you made me remember an option I was considering when I was starting this project: flip the servo to front. This way I wouldn't have clearance issues.