losi xxx

[Dunc]

Originally Posted by paulj

One thought springs to mind here which way does the motor spin in a 2wd? I've not got one to hand here, but depending on the direction of rotation it would want to either lift the front wheels or push them into the ground I'm sure this must have been thought about in 2wd transmission design? Mind you there are forces from the gears and diff spinning in the box and the pinion/spur too any ideas?

Correct, the motor on a 2wd spins such that the reaction torque pushes the rear of the buggy downwards (because it is mounted behind the rear axle). A classic example of Newton's 3rd law of motion. If looking at the left-hand side of a car, the motor would be rotating clockwise and so the reaction force would be anti-clockwise.

Another good example of this is helicopters. The tail rotor counteracts the reaction torque generated by the main rotor.

[Northy]

This is getting good, I'm enjoying it This is exactly how I wanted this thread to end up

G

[elvo]

Originally Posted by SHY

. When the weather is cold the viscosity is also in effect quite higher ('temperature stable' my AE).
.

SHY buddy, these people don't understand 'AE'.

[bigred5765]

Originally Posted by SHY

Much obliged Dunc!


First of all let me tell you that track is not that different from OR. It's not 2D vs. 3D, forget that. The suspension on track cars is just as important, and the oil is just as black after a few runs, I can guarantee that! The asphalt tracks are far from 2D! And after doing my first 1:10 OR race I must say that the driving style is also not that different - the basic idea is the same IMHO.

.

the suspension onroad may be as important .but when did you have to set it up to take a 20 foot impact from a landing, and i don't mean because you forgot to turn at the end of the track lol,

i made and manufactured gliders for a long time, and drag can both be good and bad, so can laminar flow, the difference between are wings we use, and one on full sized cars that work in the main is, we have no wing shape IE we use a upside down wing to produce down force, but it uses what we would call under camber. its of a singular thick thickness in a traditional wing curve shape,this produces poor laminar flow, if it was more a real wing shape IE a aeroplane wing it would produce better laminar flow and greater down force, as the air on the longer side of the wing has to travel further it also has to move faster producing a greater vacuum and down force, at less cost to drag and speed,

[bigred5765]

Originally Posted by Dunc

Correct, the motor on a 2wd spins such that the reaction torque pushes the rear of the buggy down wards (because it is mounted behind the rear axle). A classic example of Newton's 3rd law of motion. If looking at the left-hand side of a car, the motor would be rotating clockwise and so the reaction force would be anti-clockwise.

Another good example of this is helicopters. The tail rotor counteracts the reaction torque generated by the main rotor.

also its more the tyres that have a affect rather than the motor remove the wheels and try it in your hand it hardly moves then try it with wheels and tyres

[greeny]

hi all, im thinking of doing some work on my losi xxx. i was thinking about the mid motor change. is it alot of work? does it make the car any better? and do i need any knew bits to do it?

also ive been reading up on some of the convertions and is it advisable to solder the negative to he positive on a modified motor in order to get it going foward? and how would i get on about seting the timing to the euivilant that it is now with the negative and positive the other way round?

thanx jordan

[paulj]

Originally Posted by Dunc

Correct, the motor on a 2wd spins such that the reaction torque pushes the rear of the buggy downwards (because it is mounted behind the rear axle). A classic example of Newton's 3rd law of motion. If looking at the left-hand side of a car, the motor would be rotating clockwise and so the reaction force would be anti-clockwise.

Another good example of this is helicopters. The tail rotor counteracts the reaction torque generated by the main rotor.

So if the motor ran in reverse and the rotation at the diff was the same by use of gears in theory it would give more front end grip but loose you traction at the rear? How about the mid motor cars do they have the motor runing the same direction as a conventional 2wd? If not does this explain some of the differences in handling?

[paulj]

Originally Posted by bigred5765

also its more the tyres that have a affect rather than the motor remove the wheels and try it in your hand it hardly moves then try it with wheels and tyres

Is this due to the weight of the wheels or their position on the car? They also have a larger diameter and I would think that this may help exagerate the gyro effect? Could be complete b@ll@cks too

A good way to feel the gyro effects of spinning wheels and tyres is with a bike wheel, try holding a wheel flat in your hands and then flip it over, try it again with the wheel spinning and it will take a lot more effort to move it. This is one reason why a bike at speed is more stable than at slower speeds but conversely it takes more effort to change direction for the same reason.

[paulj]

On the subject of a light or heavy chassis how about a section of the track that has elevation changes and turns combined?
As you hit the top of the crest the momentum wants to keep the car rising so it goes 'light' over the crest, now combine this with a corner and your tyres are going to have less force pushing them down so have less grip and are not going to generate as much cornering force. A lighter chassis will be easier to lift off the ground compared to a heavier chassis at the same speed and will take longer to settle back down as it doesn't have the weight (this maybe better called mass by now I don't really know ) to bring it back down into full contact and full grip with terra firma.

[SHY]

Yes guys, now we're on the ball here!

@Elvo: if they pronounce the first three letters in the full name they will know what I mean... LOL! Dude, you tested some seasons ago a 'sectioned' rear wing (like Subaru first thought of I think) - was the difference noticeable?

As to the theoretical aspect, Elvo has thoroughly explained this aleady. Just give me a weeks time and I will post our long & interesting discussion. I find the topic fascinating as to full scale racing, it's very much a science that's not settled yet, just look to F1. We just gotta face that for model car racing we can't copy full scale solutions. It's a bit sad in a way, but true. The upside down wing shape for instance does not work in this scale as the air molecules are too big for our "insect wings" at this speed. But again, you'll get it all on a silver platter (in the meantime read Elvos articles). I can tell you straight away that insect wings as opposed to bird wings are totally flat, aerofoil wings and Bernoullis theorem don't scale down. A fly's wings just shove air around. I must say that that Predator car looks kinda cool, but I believe those wings are seriously undersized and too flat. Put on some big, steep wings! (If those shocks are progressive, that can be a good thing as that provides more traction. But it's probably like with Serpents Veteq at times difficult to figure out)

@bigred: yes, in full scale aerofoil wings are ideal. Since you mention gliders I can mention that I'm addicted to windsurfing as well. The sails we use are flat but curved (we adjust how much). Not ideal in theory compared to an aerofoil wing, but we want to surf both ways It works like hell! Still - let's stick to R/C - and aerofoil shapes are really 'fiddling around', we must take more extreme measures!

If you make a 1:8 scale F1 car (those bodies were used in the past, and Serpent has just made a dedicated F1 car now) it's absolutely rubbish, hardly no downforce at all. You need a big 'shovel' to deflect air (same pressure as you feel when you put your head out the window when driving) to get grip. As Dunc pointed out you can also just make turbulence. But a 'shoebox' for instance would not be very nimble when cornering etc. So it's also a matter of how the object moves through the air. The old Lolas were boxy and too nervous, the latest ones have even more grip and steering, and are also much more stable. This is due to a rounder shape and also a 'dome' in the middle. This I see is coming now also on the rear OR wings I wonder when we will see the first OR body with a serious dome in the shell itself. JC is already on that track with the Illuzion shell. Since the Pred has no shock towers in the way, why don't they... Not sure how much the EFRA rules would allow, but when looking at the TR501X shell there should be some room for playing about...

Now, of course aerodynamics is more important in 1:8 TR than in 1:10 OR. On the other hand keep in mind that the competition in R/C racing now is very very tuff, it's the minor details that decide which of the two experienced drivers get the upper hand. A 1:8 car really scoops up a lot of air and has probably tons of turbulece behind it (but no noticeable drag penalty as there's power in excess). The underside of the body probably also works as one large diffuser. This said, you can choose between different bodies and adjust the amount of trimstrip (Gurney). So just like in 1:10 OR there are choices to be made. To make a point: You can't win if you take off your rear wing... And... look at the X5's rear wing compared to the XX4's original wing. I'd ruffly estimate it to twice the effective size. And as I understand most guys leave the rear wings now with the 'rear wall' intact as opposed to before.

Something that's kinda surprising (to me at least) is that the wings and shells (for track) also do a lot at low speeds. Just try and take it off... remember that R/C cars are insanely fast relative to the size! When watching an onboard camera you see this very clearly!

Now - let's focus on 1:10 OR - what can we test? (I'm not thinking only XXX-CR)

Here's some ideas:
-5 cells, did anyone else try?
-4 cells (follow up with lower wind motors), anyone tried? Only for 2WD I think.
-put back weight in other areas, test 'when' it's slower
-LARGE & steep front wing, max out the rules - did anyone ever try it?
-LARGE & steep rear wing (combined with front), max out the rules - did anyone ever try it?
-move the cells around, use wires in stead of bars for testing
-make a wing mount directly on the rear hubs (only 4WD), look at the 1:8 TR solution. Accompanied with a monster wing.
-move the wing mount more to the front? (piano wire)
-where can I find springs & shock oil that is softer/thinner than what Losi and AE sells (that fits AE and Losi shocks)?

@Chris: I'm sure Atomic Carbon could do some interesting testing together with you? It takes skills & tools to make some of the solutions, especially the hub mounted rear wing. Only if you/them find it worthwhile of course. I'd really love to see a thin, molded carbon wing btw I once got hold of a molded carbon gurney, it was extremely durable!

Let me stress my point though: I believe the way to go is to make you car as light as it can be as to the EFRA min. weight (is it possible???). Then generate as much downforce as possible front & rear as can be done without violenting the same EFRA rules. Then work on setup and weight distribution. THEN as our last operation we can start adding weight here and there to see if it's any help or not. Anyone agree???

[bigred5765]

5 cells we run on very loose slipper conditions, loads running it in the states. we run it at tiverton before now, it takes out the torque hardly any top end speed lost, but on high grip tracks ull get left for dead buy the 6 cell boys,

[SHY]

I see. Unfortunately those running by ROAR rules must still have that cell in their car as dead weight, as rules over there state 'miniumum 6 cells' (while EFRA stated max. 6). Here up north we don't have high grip tracks, it's very far from 'blue groove'

Is it possible to use the slipper as a traction control device on low grip tracks btw? Will it wear out quickly if set very loose? (I know it's mainly intended for saving the driveline from jolts). I tried loosening it a lot on my B4 without really feeling any difference. Same for the X-5, it's slight belt skip helped on the other hand. Anyone experimented with different materials for pucks? (in 1:8 TR we experiment a lot with clutch plates, chlutch bell materials, shimming, springs, load and so on)

[bigred5765]

yeah we leave the dead or unused cell in also, it works well on low grip or loose tracks like in the the states dirt etc,
slipper can be use as a aid but shouldn't really as it kills the pads,but hey every edge helps.
the yokomo white ones are best more controlled slip

[SHY]

Thx! # no for them Yokes? Webshop link? Are there different plates as well? Do they fit both the B4 and X-5?

PS. I added some to my previous posts

PS2. If anyone's looking for upgrades for the XX4 or X-5, I've made a little something here to save you from spending 2 months vacuuming RC-forums (make sure you have sound on)

Zzzzzzzzz...

[elvo]

Originally Posted by SHY

Dude, you tested some seasons ago a 'sectioned' rear wing (like Subaru first thought of I think) - was the difference noticeable?

Not really

It's standard in the XXX-CR kit now though...

[SHY]

Hm... I thought it would be just 'fiddling around' yes. I saw some guys use it for 1:8 TR as well, but not anymore...

Subaru rear wing: (for those who haven't seen it)
http://www.tamiya.com/english/produc...apan/index.htm

XXX-CR:
http://www.teamlosi.com/Products/Def...rodID=LOSA0032
-a totally new wing with sections, or did they just put a front wing on top of the rear wing to make two extra fins? (saw a local hero do that)

Btw. as I see it a lot of the 1:10 OR cars have quite large drag downforce devices in the front, namely the front shock tower. For instance the S4 and the BJ4 have a quite large area vertical carbon plate in the front.

Elvo my man, as to theory I have a few detail questions:
-will a totally vertical plate generate more downforce than one that is angled (I presume yes)?
-will a vertical plate generate more downforce if the top is totally level as opposed to rounded/other shape? (more 'gurney like')
-will the turbulence from a large area and vertical front shock tower (or wing) decrease the effect of the rear wing? (do a drag downforce device request 'clean air' or can it work with air that's already turbulent?)
-If a vertical plate (wing) provides more downforce than an angled one, how about a plate that's vertical and then at the top bent forward (like a large Gurney)?

A sidetrack:
I btw know a cracy norwegian that used to be a speed windsurfer. He mounted a small wireless camera (normally used on his sail) on his 1:12 car to see how the suspension was working. Did you guys see the Klemm Films onboard video from Vienna? Supercool!!!

A TOTAL sidetrack:
http://www.oople.com/rc/photos/tiverton2007national/
Elvo, is that our Danny boy?

[rich_cree]

I'll give you these two points to discuss amongst you:

1. In 2wd off road the single bigest improvement in laptime tends to come from when you can hook the power up best, i.e. get lots of drive off slow turns (assuming your corner speed, balance or bump handling isn't really bad). In this situation where you have excess power and are having to delicately feed the throttle in, wouldn't extra load on the tyre through extra weight be beneficial to lap time?

2. What if the plastic chassis we use (graphite or plastic stylee) are way stiffer than we need already and the difference in feel is purely down to the shock absorbing characteristics of the material when it physically hits the track surface, i.e. how much energy is returned in the form of a kick, and how much is absorbed (damped) by the material?

[elvo]

Originally Posted by rich_cree

2. What if the plastic chassis we use (graphite or plastic stylee) are way stiffer than we need already and the difference in feel is purely down to the shock absorbing characteristics of the material when it physically hits the track surface, i.e. how much energy is returned in the form of a kick, and how much is absorbed (damped) by the material?

Couldn't agree more with that. People talk about flex in absolute terms, but I feel it's more a matter of absorbing energy than of displacement - torsional or otherwise.


And yes, that is "our" Danny Boy :-)


There's a pic on here somewhere of Danny McGee bolting on an almost vertical front wing..flap..pice of lexan. With comments on how it worked. Lemme see if I can find it.

[elvo]

Originally Posted by rich_cree

...when it physically hits the track surface,

... or when the shocks "pack up" from hitting a bump or jump at speed.

[rich_cree]

Originally Posted by elvo

... or when the shocks "pack up" from hitting a bump or jump at speed.

Good shout, never thought of it like that