Attitude Control

Something I didn’t realise about gas-powered RC offroaders (until I got my own recently) was the amount of control one has when they are airborne.  I’ve seen many examples of them in action, and I thought jumping was all about the speed and angle of entry.  Not so.  Here’s what I’ve worked out through trial-and error (including a broken front suspension wishbone) at the local BMX track:

  • Speed of entry is critical for distance.
  • Angle of the ramp is critical for height.
  • Landing attitude is controlled by throttle (or lack of) and brake in the air.  And possibly a tiny bit by how you leave the ramp (under power or not).

Here’s how throttle control works for me.  Imagine a tabletop jump (or a long double).  Assuming I have the speed to carry the truck across the top and onto the downslope, here’s what happens:

  • If I back off the throttle in the air, the nose drops way down, resulting in a heavy nose landing and often a crash (rollover or cartwheel)
  • If I keep the throttle pegged in the air, it flies flat or slightly nose up, resulting in a rear-wheel landing. Better, but still rough and sometimes resulting in a rebound which causes a rollover.
  • If however I keep the throttle on just long enough, and back off as I clear the ‘table’, the nose drops nicely and the truck lands perfectly parallel with the downslope.  Very smooth.

I seem to have got the grip of this fairly well, such that I can adjust the landing attitude for most jumps.  Short triples are still a hassle because it’s hard to judge the entry speed and decide whether to clear one or two of the jumps.

[tags]rc, radio control, jumping[/tags]

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  1. Hmmm I don’t remember that from my physics classes, but I suppose yeah if the wheels slow down the spinning energy has to go somewhere right?

  2. Sure! I replaced the broken suspension bit. Damn I forgot how cheap this hobby is once you’ve overcome the initial purchase: a set of all 4 upper and lower swingarms for the front suspension was $8.

  3. A set of things for $8…?! Someone has their retail psychology calibration all wrong. It’s not about constant markup ratios, it’s about how much you would pay on the spot having travelled all that way for something that your machine won’t work without… viz. Sony’s earbud spongy bits: new headphones with spongy bits = $35; set of replacement spongy bits = $20. Awesome!

    And meantime, Ben, go play DirtBike for an hour or so and rekindle that instinct for throttle on = backspin, throttle off = nosedive. Good-o!

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