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3D tisk - zakázky a vlastní projekty
WLtoys A979 Battery (EN)
2016-01-09: High capacity battery upgrade

If you read my previous article carefully, you might have found a notice, that there has been a possibility of mounting a big 6-cell NiMH battery pack into this tiny car. I wasn't joking...
What do you need?
  • A 3D printer ;)
  • A pair of connectors: a BEC connector same as on the original battery, PSH (sometimes called "Tamiya") connector opposite of the NiMH battery pack
Using some 3D creation software, design two parts – front and rear battery pack holder. That's a very simple exercise, you only need to be careful about precisely measured dimensions on the car. 3D Print it, preferably from ABS, PETG etc. I wouldn´t recommend PLA in this case as the rear holder is very close to the electric motor, which can get hot when running, and thus the PLA will degrade.
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I decided to mount both holders on the car's differential casings using the already present screws. That's a noninvasive solution, which can be removed anytime. Also the antenna must be pulled out from the standing pole and left lying on the side.
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Solder the two battery connectors together, I had the BEC with a pair of wires, so I used them.
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Results:
  • The battery pack's nominal capacity is at least 4 time bigger than the original pack. That means much longer running time to get the right feel of this fast car (that's why I'm doing this). That also allows me to finally record some off-road video.
  • The battery pack is much heavier compared to the original LiPol pack. That means, the car now "sits" more on the ground. I like that ;) . We'll see the influence on the car's behaviour in the upcoming video.
  • And finally some very interesting result, that I didn't expect in such a light car. My NiMH battery pack is not capable of providing enough short-circuit current compared to the original LiPol pack. It means, the ESC gets restarted when you press instantly full-throttle (within a few milliseconds). The electric motor acts as short-circuit for a short moment, thus battery voltage drops under such level, which is no more acceptable for the ESC to run. The car stops.
    If you press full-throttle a little more slowly (250 milliseconds or so), that's enough to move the electric motor and prevent battery voltage from dropping too much. If I use a LiPol battery pack from the HG P402 (same 6-cell size), this does not happen, because these LiPol's are a much harder power source.
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2016-03-03: NiMH battery pack upgrade

As already noted, I've 3D printed my NiMH battery pack holders and mounted them on my WLtoys Vortex model A949 . Suprisingly, there is exactly the same amount of space above the front axle as on the A979 , so I really didn't need to change the 3D model for the holders.
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I hardened the front and rear springs (dismounted and stretched by hand :) ) and mounted the lower shocks's joints into their spare positions closer to car's center.
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That has helped me to gain some extra millimeters of road clearance (because I'll be driving primarily off-road) and also keep the car above the ground with the heavy battery. I can change car's setup to on-road configuration again moving the joint to their original positions.
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After a few short test runs the car is much more stable when driving. Of course, that's the effect of huge mass added to the chassis. Also, it is much less agile when cornering (more sliding!), so the drive looks more realistic. Stay tuned for first outdoor rally cross tests and video :) !

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