Losi xxx mid motor nosedives?

[Ferret]

Today I finally completed my Losi xxx mid motor conversion and took it for testing on the the track.
I was really surprised how well it handled "out of the box" with my guesswork setup.

However, there was a fly in the ointment; it had a strong tendency to nosedive off ramps unless I launched with a lot of throttle, to the extant of actually flipping forward many times.
The car uses an extra gear so that the motor is spinning in the same direction of the tires.

Did anyone else with a conversion experience this?
Any ideas how to resolve it?

Thanks,
Avner.

[Benh]

What's your drag brake settings, or did you not come off the throttle?

[CBRDEAN0]

Try some lead under the lipo - the xxxCR was designed to have a motor out the back and NiMH cells.

And orange springs would seem a bit hard for the rear - I would have gone with a softer setup - perhaps pinks.

The hard rear end will probably be kicking the back up over the jumps

[Ferret]

No drag brake.
It did happen off throttle, but in the same situations my standard xxx-cr would just get a little or no air. It would not nosedive, land on the front bumper ald flip over.

I could drive around it in testing, but I am real apprehensive about racing the car like this, a small mistake and it's a long wait for the turn marshal...

[CBRDEAN0]

you could always look at the Atomic Carbon CR2 thread (mid engine xxxCR ) and try the setups from there.

The CR2 has won a national so they are pretty dialed with the car.

[Ferret]

I am using the innermost lower shock mounting hole so the spring are relatively "soft". I started the day with reds and the car understeered, switching to oranges made the car pretty neutral.

I want to know if this nose dive tendency is common to mid motor conversion, or particular to mine. It feels too severe to be a simple setup problem. I've been racing conventional 2WD buggies for more than 15 years and never had one nosedive like this regardless of the setup.

I feel my conversion also had a tendency to roll over to the side but this was not as severe and felt like it could be impruved with a better setup.

I'm concerned that maybe the center of gravity is too high or the wheelbase is too long.

[CBRDEAN0]

Originally Posted by Ferret

I am using the innermost lower shock mounting hole so the spring are relatively "soft". I started the day with reds and the car understeered, switching to oranges made the car pretty neutral.

I'm concerned that maybe the center of gravity is too high or the wheelbase is too long.

I would have softened the front first. And put some weight further forward.
Then used softer springs on the rear and moved the shock bottoms out.

If you have used the same wishbone mounting block as the std setup - the wheelbase should be the same as the xxxCR.

How could it be longer ? - have you made a custom rear plate or wishbone mounts ?

[Ferret]

You're talking about track width. I got a long wheelbase by by using a xxx-T chassis for my conversion.

[lochness42]

My XXX-CR mid conversion didn't have such problem - it was surprisingly stable in air, I just had problems with spinning out of corners. I just have custom made slim alloy heavy chassis.
When I got my X6 and I added weight as it was recommended I had nose diving car as well, I moved part of weight to the rear and is very nice to drive now.

p.s. here is link to my conversion for comparison with yours http://www.oople.com/forums/showthread.php?t=27655

[CBRDEAN0]

Originally Posted by Ferret

You're talking about track width. I got a long wheelbase by by using a xxx-T chassis for my conversion.

No - i was talking about wheelbase (length of car) - i assumed it was an xxxCR chassis used

Can the conversion not be done using a standard xxxCR chassis ?

Looks like you have enough room the run the shorter chassis.

[migsy]

try running flu yellows at the back with a 35w oil and orange piston

blues at the front with 30-35w oil and orange piston.

works for me.

cheers.

[Ferret]

Lochness,
regarding the weights you used on your X6, what were the original and final locations?

CBRDEANO,
sorry, I misunderstood what you meant about the wishbone mounting block. I decided to use the longer chassis because the track I run the car at is very bumpy and when dry very slippery so I wanted a very stable car.

Migsy,
did you have nosediving before using this setup?

[migsy]

Migsy,
did you have nosediving before using this setup?[/quote]

yes, i had the same prob. i now use some sticky weights placed around the chassis to help keep it more flatter when taking the jumps. also keep the throttle on abit.

to stop the front popping up, i made a weight "35g" out of melted led and left it to dry in a mould so it would go straight into the the bulkhead, upinsde where the bumper screws on to the chassis.

hope that helps

[CBRDEAN0]

Originally Posted by lochness42

p.s. here is link to my conversion for comparison with yours http://www.oople.com/forums/showthread.php?t=27655

I remember reading this - looked good. Was it longer wheelbase too because you have a stick pack up the centre of the chassis ?

Looked cool with the cat shell on

[Ferret]

Originally Posted by migsy

yes, i had the same prob. i now use some sticky weights placed around the chassis to help keep it more flatter when taking the jumps. also keep the throttle on abit.

to stop the front popping up, i made a weight "35g" out of melted led and left it to dry in a mould so it would go straight into the the bulkhead, upinsde where the bumper screws on to the chassis.

hope that helps

I'm a little puzzled, are you saying that you had the nose both diving AND popping up?

I seems to be a contradiction to me, to fix nose dropping you need more weight to the rear and to fix nose popping you need more weight to the front.

[lochness42]

Originally Posted by Ferret

Lochness,
regarding the weights you used on your X6, what were the original and final locations?

I cut one 50g weight into halves and moved it from servo to sides of motor. That cured my problem completely. I don't remember exact weights and positions off my head of rest but can check it if you want.

[lochness42]

Originally Posted by CBRDEAN0

I remember reading this - looked good. Was it longer wheelbase too because you have a stick pack up the centre of the chassis ?

Looked cool with the cat shell on

I'm not sure what was wheelbase of std car as I've got both disassembled, but it has wheelbase of X6 - I used it as reference when I was trying to figure out how to place battery along chassis. Biggest help to be able to run stick pack up the centre was using standing low profile servo. Everything is quite tight fit - I've got only about 1mm gap in front and rear of battery.

[migsy]

these days our motors are so powerfull, i use a 7700kv and it just so powerfull the car was up on its back wheels.
how you can say its a contrdiction i dont know. there is a element of balance with these and the name of the game is to keep it on all 4 wheels.

get it weighted up right and it should jump perfect and keep its nose down on accelaration.

[madmax]

hi m8 nice conversion, as regards to the nose diving problem i would first try a softer rear i would try a yellow spring with blue piston and 25wt oil thats what i run at southport and bury and find it very stable. if not that have you thought about a bigger rear wing x60`s and x6`s run a larger rear wing for this reason, as ive experimented with different wings for this reason. also you have to remember that with the motor rotating in the same direction you have the toque of the motor wanting to push the front of the car down.

[Ferret]

If I summarize what understood; the consensus seems to be that the mid convrsions do have a tendency for the front to drop down off ramps, and that the common cures are soft rear springs, weights to the rear and big wings.

I will try these changes and see how it goes.

Thanks everybody,
Avner.