Test driving the Piranha P2

aaron_ · #1 26-11-2006

As this is my first post on the "new" forum, I'd like to introduce myself first.
My first contact with rc was quite some years ago. I first tried planes (5min flight, 1 week repair), then boats (well, not much action going on when there's no big enough pond around) and finally came to offroad rc-racing.
I'm doing it only just for fun, so no sanctioned racing for me. Apart from driving these things, I'm quite into the technical aspect so I did several articles on ball diffs, dampers, etc. and reviews which you can see at www.offroad-cult.org.

Regarding my reviews - big thanks to jimmy for showing what great photos should look like!! To put it bluntly: they taught me not to show just "something" but use depth of field, angle of view etc. to create a special "feeling" - though it's sometimes hard to get such things with a small sensor compact/bridge camera.

Now, let's move on:

The piranha P2 is a concept car of a friend of mine that's aim is to show off what is possible with today's technology.
Apart from several donor parts at the rear and front end (which are not hard to guess

) everything from the carbon/kevlar tube chassis up to the PET body is handmade.

The P2 may not look like a typical 2wd buggy, and neither does it handle like one. Driving the piranha feels more like driving 4wd since the rear end is soo stable yet responsive. (now I understand what Charles Sinclar - www.2wdrc.com - meant when he compared the rear end of conventional 2wds to a pendulum)
The P2 is not only stable but very predictive, so there are no nasty tendencies while accelerating, braking or cornering.
On the other hand, there are still some things to get right: Steering isn't quite where it should be, featuring only ~ 70% of other 2wds steering throw, which together with the not yet tuned front suspension adds quite some understeer.

Because of its stable driving characteristics, the piranha P2 could benefit from a good amount of oversteer which would make it very agile, yet controllable I guess.
However, due to LIPO battery (NiXX Sub-C won't work weight-wise), some other nasty stuff and a mere 1200g, it will never be legal under sanctioned racing.

xx4-nutter · #2 26-11-2006

good god !

that thing looks shit hot

very nice, any pics of the guts ?

PaulRotheram · #3 26-11-2006

Pics of under the shell:

http://30486.rapidforum.com/topic=101474415088

Lew · #4 26-11-2006

Well that look's shit hawt!!! so slim though :O!! good job on making it.

xx4-nutter · #5 26-11-2006

Quote:

Originally Posted by PaulRotheram

Pics of under the shell:

http://30486.rapidforum.com/topic=101474415088

hahaa a few mins after i noticed

cheers

jimmy · #6 28-11-2006

Hi Aaron and welcome! Thanks for the kind comments, the photos look GREAT

indeed, this project just looks amazing! really like it! The body off shots are really really cool.

BenG · #7 28-11-2006

Dude, I love that car. I wanted to build a 2wd car not too differnt to that, only with a Bj4 transmisiion. How did you make the chassis? Is it possible to buy a kit to do it?

Thanks

Ben

jimmy · #8 28-11-2006

yeah you can buy it, is it called pre-preg carbon fibre or something ? There are some online shops that sell the stuff, you lay it up over your mould with some special epoxy juice and leave it to harden / cook it I think.

BenG · #9 28-11-2006

Quote:

Originally Posted by jimmy

yeah you can buy it, is it called pre-preg carbon fibre or something ? There are some online shops that sell the stuff, you lay it up over your mould with some special epoxy juice and leave it to harden / cook it I think.

Thanks Jim

I would like to thank aaron, that design has inspired me to finish mine. Lookign at the moulding technique has solve a big problem for me too, so thanks alot my friend

I dont need my chassis machining no more yay

DCM · #10 28-11-2006

well, the resin you use depends on your procedure, but you must get advice on what to use, cold cure with pre-preg sheet is the best I would assume. The more weight you can put on it, the better, as you get more carbon than muck, which makes for a stronger lay-up.

Be warned, do not get the two part mix, as it generates an exothermic reaction (gives out heat), and if you put a tiny to much accelerator in the mix, you will have a lot of smoke at least, at worst, nasty fire and toxic smoke.

So, pre-mix stuff is good.

BenG · #11 28-11-2006

Steve, how would I go about applying weight to that sides of the design? If it was curved? Could I make the mould so I can just put weight on top? I think it will have to be cold mix, due to the fact I cant really heat it in the oven

DCM · #12 28-11-2006

you could make a pug and mould affair, so you layup the carbon on the plug, then slide the mould over, there are ways and means.

BenG · #13 29-11-2006

Quote:

Originally Posted by DCM

you could make a pug and mould affair, so you layup the carbon on the plug, then slide the mould over, there are ways and means.

I see, so you kinda mould it from both sides

albertobdq · #14 29-11-2006

Great design!!! I really like it!!! the issue with lipos isn't weight, you can make the car heavier just making the chasis thicker.

I'd like to drive that amazing machine.

aaron_ · #15 30-11-2006

Thanks for the kind comments!

albertobdq, the car weighs ~ 1200g and minimum weight is 1474g I guess - so the chassis has to be something of a carbon-fibre brick to bring the wheight up

On the other hand, more weight will set the CoG way off: look at the X-Factory X-6: with a heavier battery, it has to be split in a 4+2 pack to move more weight back to the rear end. You'd never get away with the weight of a 6 cell NiXX pack in the piranha's layout because it will move the CoG too much to the front.

albertobdq · #16 30-11-2006

Hi Aaron, I'm just thinking aloud...

Maybe a motor plate made from iron, or just T6 rear A-arms could do the trick, or aluminium wing mount, you can also go for an aluminium rear shock tower. Going a little crazy you can even think about a machined gearbox. All these things are heavier and place more weight at the back.

I believe that a 4mm thick chassis could also help on a car so light.

I'm aware that some of the ideas beside moving CG further back (and adding weight) will also rise CG and that have to been considered and tested.

I really love these desing and believe that with some mods you could use Ni-Mh cells, with minimum legal weight and perfect CG.

aaron_ · #17 01-12-2006

BTW, if you want to know how it all started ~ 1 year ago, take a look at the Piranha P1!

It's in German, but the pics are self explaining.

Performance-wise, it was - well.. not so good

Chris Doughty · #18 01-12-2006

I have to say Aaron, full credit for such a unique car! both the P1 and P2.

I have played with mid-motor and it looks like ou are using a XXX box, you should be able to reverse the box with some dremel work, from the looks of your car this should be easy for you to do. the gear cover is not a good fit after though. might need tomake one of those too!

OldTimer · #19 02-12-2006

Aaron - Really nice job and refreshing to see something a little different.

Tyrc - The best place to get Carbon fibre fabric and epoxy is http://www.cfsnet.co.uk/ they are pretty fast, look under Fibreglass mat & fabrics > Carbon Fibre fabric. And if you want a pretty good guide how you do it have a look here http://www.mashie.org/guides/cfbalsa01.html, and there is no need to pop it in a oven

but don't use the balsa, just plenty of layers of CF.

Attached a pic of what kind of things you can do with it

aaron_ · #20 03-12-2006

Just to clarify: I did not build the piranha, credit goes to Mad Max as stated in the first post.