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Old 05-29-2013, 07:49 AM
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Foxy
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Default RE: Hpi Sprint 2 flux upgrade 90+mph

Perhaps the people on other forums didn't know how to go about telling you that what you've listed there is not suitable for the stated goal.

For a start, 1/10th is not the best scale to do this with. 1/8th would be much easier. 1/10th are small and light and will be prone to take off at anything above 60 mph. Tiny rocks will have a dramatic effect on direction of travel as well as eat your belts in an instant at those kinds of speeds. It is achievable with a belted 1/10th touring car, but not without significant and expensive trial and error regarding the necessary body modifications to generate enough downforce to prevent the car taking off, but not generating so much drag that the goal cannot be achieved, as well as thoroughly cleaning the surface you will run on (yes, all of it).

Then there's your choice of electrics...the biggest issues are the motor and battery. The motor is a 3500kv, this means it will turn 3500rpm for every volt supplied. 2S batteries nominally supply 7.4v. 7.4 multiplied by 3,500 equals 25,900. Consider that your average .12 nitro engine turns 40,000rpm and will get a touring car to about 45mph on moderate gearing. Electric has a torque advantage, but I highly doubt that the gearing you will require to hit these speeds will even fit in the car...for example, to hit 70mph you are going to need an 80 tooth pinion, which doesn't exist, so int he first instance you are going to need a MUCH faster motor. Regarding the battery, you are definitely going to need to go 3S (11.1v) if you are serious about going over 60mph, but the gearing to achieve that with a velineon 3500kv even on 3S again, does not exist.

While we're talking about motors, I should also point out that you would be better off with a 4-pole. The stock motor in the Flux is a fairly quick 4 pole 5900kv, a motor which is SIGNIFICANTLY faster and more powerful than the Velineon. The Velineon is actually a huge downgrade from the stock motor. The stock motor is actually a decent choice for a 80+ speed car.

Why are you buying Traxxas stuff anyway? Did someone tell you it was good? They have very few products that could help you achieve your 70-90mph goal, and all of those products are designed for 1/8th cars.

If you said to me, I want to make my sprint 2 flux go 100mph, I'd say get the Mamba Max Pro speed control, a motor with at least 8500kv, run it on 3S and gear it to the moon.

You also realise (I hope) that this car that does 100mph will be able to go up and down once, then require time to cool? It won't be any good for anything else except speed runs, and very short ones.

If I were you, I would return everything, not buy the Sprint 2 Flux if you haven't already. Instead get a second hand OFNA DM-1 or GTP2E and a 2650kv motor, run it on 6S batteries and stick a 25t pinion on it. That should get you there or thereabouts. Bear in mind you will need a lot more money than what this traxxas stuff cost before you are even hitting 80 no matter what you choose. If your goal is a 100mph rc car as cheap as possible, again, a whole different set of recommendations would be put forward.