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2 Similar RCs w/ Different Speeds

2 Similar RCs w/ Different Speeds

Old 03-11-2021, 02:03 PM
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Questions?? 2 Similar RCs w/ Different Speeds

I am a novice RC user & have been searching on the web for an answer to this for a week or two now. I bought my kids a couple of generic hobby grade RC trucks (which I am very happy with) from different sellers on Amazon. Both trucks appear to be by the same manufacturer. With the shells removed, they are nearly identical minus a couple aesthetic differences. However, one truck is quite a bit faster (as it was advertised when I bought it). I'm just curious why the one is faster. I've gone through the parts lists in the instruction manuals & except for the tires & batteries, the systems use the same parts.

Parts list for slower (sold by DEERC):
  • RC 390 brushed motor (M16034V2)
  • ESC/Receiver (M16032V3)
  • 7.4v 800mAh Li-PO battery
  • wheel diameter: 78mm
  • wheel width: 41mm
  • gear ratio: 1:10.71
Parts list for faster (sold by Fcoreey):
  • RC 390 brushed motor (M16034)
  • ESC/Reciever (M16032V2)
  • 7.4v 1000mAh Li-PO battery
  • wheel diameter: 75mm
  • wheel width: 40mm
  • gear ratio: 1:10.71

The conclusion that I have come to by watching some tech videos on YouTube is that the ESCs are programmed differently.But as I lack experience, I don't know for sure that is the reason. The videos that I found about ESC programming didn't specify anything about the speed of the machine. If anyone has any insight for me, I am very curious about this.

I don't yet have permission to create hyperlinks to external sites or add images, but if you would like to see them side by side with the shells removed you can translate this link: postimg dot cc/zHKSjMkz/6ef13186
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Old 03-14-2021, 04:19 PM
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All things being equal... larger wheel diameter will produce a higher top end speed...
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Old 03-16-2021, 01:49 PM
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Makes sense to me, but the truck with the larger wheel diameter is the slower one (lower top speed).

These are the two models:
  • Haiboxing 16889 (slower) (sold by DEERC)
  • Haiboxing 16890 (faster) (sold by Fcoreey)
I have swapped motors but the 16890 is still faster. Both motors have the same number on them: XO 390-6022-63D FF (I don't know what any of that means except I think the "390" has something to do with the size of the motor). I've also swapped batteries. But I need to do a little more testing to be sure (got to get my son to help me so we can test them side by side because I don't have a speedometer or radar gun). As ESC stands for "Electronic Speed Controller", I'm assuming it can serve as a speed governor & be programmed for different speeds. Is that accurate? The videos that I looked up showed all different kinds of settings, but nothing about speed.
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Old 03-16-2021, 02:23 PM
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probably a combination of the battery being slightly higher mAh's which will maintain a slightly higher voltage, plus the difference in motor (one says v2 so gotta be something) and the biggest thing would be the tire diameter.
This greatly affects the 'roll out'.. or the distance traveled by the vehicle for each revolution of the motor. Remember that math you were to learn back in middle school? Here we are..
tire diameter * 3.14 * (pinion / spur) = rollout
foam tire racing pretty much lives by it.

one car may start off a little faster and the other will have higher top end later on so it depends on how far you are going with them.
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Old 03-16-2021, 05:32 PM
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With the motors swapped, they appear to be around the same speed. Swapping battery doesn't seem to make much difference.

Edit: I need to get some equipment for testing this stuff.

Last edited by AntumDeluge; 03-17-2021 at 03:16 PM.
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Old 03-21-2021, 01:24 PM
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Could be transmitter settings.
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Old 03-22-2021, 04:49 AM
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I wouldn't overlook things like build variability too. If these are low-cost or entry-level RCs and came ready-to-run, the slower one could have more drag in the driveline or other issues. The ESCs could be capable of different current loads and as was said, the transmitters may be adjusted differently. Each ESC has to be calibrated to the radio in one way or another, so if that wasn't done correctly that can influence things too.

Since you said the motor swap made them approximately equal that explains at least part of it - and again - those RTR motors are likely very low cost, mass produced pieces. So they could be different internally (different part numbers) OR you could just be seeing part-to-part variability.

I understand the desire to understand "WHY" but for a cheapie car, if the kiddos are happy, call it good. I certainly wouldn't buy any specialized equipment to analyze them...unless you just like a challenge.
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Old 03-22-2021, 05:56 AM
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Not sure if the transmitters offer much in terms of adjustments, but that could make a difference if throttle endpoints are different.
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