Le pourquoi du comment sur les configs 1/8 à un ou deux lipos

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Le pourquoi du comment sur les configs 1/8 à un ou deux lipos Empty Le pourquoi du comment sur les configs 1/8 à un ou deux lipos

Message par Pulse le Mar 3 Mai 2011 - 19:41

On compare souvent les deux et voilà ce que m'a répondu un gars de chez rctech qui conçoit des châssis chez HHH. Désolé c'est en anglais Razz

Quote:
Originally Posted by Pulse_
I'm wondering why they did 2 lipos setups actually. As a guy said above 1 lipo per side means that the car can't be balanced as soon as the motor is on one side.

Answer:
As a necessary prerequisite to designing and manufacturing hi-performance chassis for electric 1:8 scale buggies I have personally logged hundreds of hours in R&D related to this very topic. The results of my on-going study show that you can actually achieve a perfectly balanced buggy from front-to-rear and from left-to-right with either a single-battery configuration or with dual-batteries in a saddle pack configuration.

In response to the quote from Pulse, you are correct the weight of the 2 lipos (1 per side) cancel each other out, however, the weight of the motor (the 2nd heaviest component) can/should be canceled out by the sum total weight of the steering servo, ESC, Rx, Rx box, steering servo linkage, steering servo mounts, servo saver, etc. which can be precisely calculated and positioned for optimum balance.

Of course, you can balance virtually any RC car on all four corners by just adding weight to the areas that need it. However, to balance any given RC vehicle on all four corners without the addition of any weight (actually reducing weight whenever possible), and by simply using the weight of the required components arranged in such a way that will maintain their functionality while achieving equal balance on all four corners, and without raising the center-of-gravity(CG) of the vehicle (i.e. stacking components etc.), can be a somewhat difficult task to say the least.

When using a single 4s LiPo battery in the HHH Ve8 chassis I found it to be relatively easy to balance the vehicle from front-to-rear and from left-to-right without adding any weight. This would be a measurable improvement for the majority of 1:8 scale RC cars and will gain you most of the noticeable benefits from having a balanced vehicle. However, it is not the same thing as balancing on all four corners which is substantially more difficult to make happen and has proportionally fewer noticeable benefits that can be gained. I do not believe it is (reasonably) possible to realize either of these standards for balance with several of the single-battery configurations currently being used in the 1:8 scale platforms of at least a couple of the major manufacturers, without the addition of weight.

The only way I have been able to achieve equal balance on all four corners of a 1:8 scale buggy while also maintaining a full race ready weight below 8 lbs., is with dual batteries in a saddle pack configuration. As it is explained above, this will likely yield a few additional benefits that may only be noticeable to those with very advanced driving skills. Therefore, by itself, the ability to balance all four corners is NOT the reason why dual-batteries in a saddle pack configuration can have an advantage over single-battery setups.

There are measurable improvements in performance that can be realized when running dual-batteries in a saddle pack configuration. These advantages are primarily the result of the combined total effect from the following three features which are typically not found in single-battery setups.

1) Centered Driveline: By centering the driveline to allow for balanced placement of dual-batteries the more important by-product of this is that it also effectively eliminates all of the left-to-right scrub that occurs with an offset driveline. Scrub is the equivalent to driving your 1:1 scale car around town with the parking brake just slightly engaged 100% of the time. The more severe the offset = the more severe the scrub = the more engaged the parking brake.

2) Improved Balance: As mentioned above, this by itself offers only minimal gains. But in combination with these other features it can amount to substantial performance increases due to the total weight of all the components being more narrowly and uniformly distributed along both sides of the centerline axis of the chassis. This results in a more nimble vehicle that transfers the load quicker and smoother from side-to-side and front-to-rear.

3) Lower Center-of-Gravity(CG): The single heaviest component on a 1:8 scale off-road buggy is the LiPo battery. Sometimes it is even more than double the weight of the 2nd heaviest component which is the 40-42mm brushless motor. A typical 4s 5000mAh - 5200mAh ROAR Approved LiPo battery weighs approx 600 grams (1.32 lbs) and all of that weight is typically perched on top of a raised battery tray and rises well above all of the other components on the chassis. As you can imagine this will promote a number of undesirable handling characteristics i.e. traction rolling, instability when jumping, etc. the list is long.

By running dual-batteries in a saddle pack configuration (preferably secured directly to the chassis without a tray) you are lowering the elevation of the entire amount of weight/mass from the battery (approx. 600 grams total) by 50%. Essentially slicing approx. 300 grams of weight off the top, from the highest point on the vehicle and repositioning it to the lowest point possible which is directly against the chassis. It shouldn't require a PHD in Engineering to understand the potential benefits that can be realized from this.

Pulse

Nombre de messages : 3034
Date d'inscription : 21/05/2009

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Le pourquoi du comment sur les configs 1/8 à un ou deux lipos Empty Re: Le pourquoi du comment sur les configs 1/8 à un ou deux lipos

Message par Hugo le Mar 3 Mai 2011 - 19:55

Perso je trouve que mon losi est pas trop mal équilibré, apres je serais curieux de tester un buggy équilibré au gramme prés Very Happy

Par contre un moment le mec dit (si j'ai bien tout compris) qu'il fraudais fixer les accus directement sur le châssis pour gagner en hauteur et donc en poids mais le règlement nous oblige a avoir un bac a accus non? scratch
Hugo
Hugo

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Message par carino le Mar 3 Mai 2011 - 20:50

les explications sont bonnes, plus le poid est bas mieux c'est.
plus le poids est équitablement répartit, mieux c'est.
tout ça c'est de théorie, que je ne remet pas en question, je suis même d'accord, mais quel serai le gain à notre niveau 7 ou 8 secondes au tour ? je ne pense pas.
carino
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Message par Pulse le Mer 4 Mai 2011 - 22:28

Je relaie une explication qui me semble assez claire, mais perso j'ai pas de préférence une config en saddle à ses inconvénients (pièces ne plus, manque de commodité, suppose de changer ses lipos etc...). Par contre quel que soit le niveau du pilote le châssis joue tout de même. Par exemple la DEX410 a été une petite révolution en 1/10 et a permis a beaucoup de tourner plus vite qu'avant. Je ne dis pas que ce sera le cas avec la DEX408 mais l'équilibre des masses peut très vite se ressentir au pilotage. Je pense qu'il y aura tout de même des différences entre un châssis nitro converti et un châssis pensé à 100% pour le brushless. Après pour du bashing c'est clair que ça n'a pas la moindre importance Wink

Pulse

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