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  1. P

    Kv * turns = constant?

    Wow that thread is gigantic! I'm having a lot of trouble following the discussion. From what I can tell, liveforphysics agrees with me? Let's use pronghorn's notation and speak in math terms. Sorry, it is my weakness here, but I think I have difficulty understanding the English. Equations...
  2. P

    Kv * turns = constant?

    What if we also double the gear ratio in addition to doubling the kv? We get the same speed, torque, and power for the same voltage and current input. But we also have 1/4 the resistance, so effectively double the current capability, and double the max torque?
  3. P

    Kv * turns = constant?

    Quick question, for a given motor geometry, is Kv proportional to 1/turns? Corollary to that question, for a given motor geometry since motor_internal_resistance = constant * turns^2, motor_internal_resistance = constant / Kv^2. Max_motor_current = constant * Max_motor_power = constant *...
  4. P

    RC motors, rated current and power?

    Gotcha, makes sense. Thanks guys!
  5. P

    RC motors, rated current and power?

    This is for a skateboard application, but the motor principles should be the same. I'm very curious why skateboards seem to use much smaller motors than bike guys, I assume its because bike guys go faster in general. Boosted seems to achieve quite reasonable performance with a pair of (what...
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    RC motors, rated current and power?

    Why do RC motors have power ratings quoted? What does a power rating even mean, since 1 kW at 10V draws much more current and produces much more heat than 1 kW at 100V? Is the quoted power just a made up marketing term? Take a Turnigy SK3 6374 192 Kv for example, specs quoted by HobbyKing...
  7. P

    Integrating Lipo Charger into E-Board

    Why not just make the wiring loom from the second photo, leave the charger off-board, and plug in the primary serial-charging leads when you get home? It's what I did since I didnt want the extra weight of the charger on-board. The plan was also to only balance charge when necessary (I've got...
  8. P

    ESC restarts itself?

    Good ideas with the motor testing. My results: Option A Yeah, I have no idea what I'm doing... My multimeter says each of the three leads are all shorted together, but I dont know if thats normal. I can't really test the resistance since my multimeter basically says 0 resistance, I guess I'd...
  9. P

    ESC restarts itself?

    Yeah, I've been fiddling with the programming, changed the timing, acceleration settings etc etc successfully. I've occasionally gotten the motor to turn a few degrees, but never as much as even a quarter turn. I've recalibrated the GT2b trigger throw as well. Yup, ESC definitely connected to...
  10. P

    ESC restarts itself?

    Pics and video below I dont think they burned out, given that the test ride was so brief, but I'm not sure how to tell frankly. Didnt see any sparks or anything. Dont think I hit a rock and nothing got jammed at any point (or I would have been thrown off the board). I dont have another motor...
  11. P

    ESC restarts itself?

    I tried fiddling with motor timing, and within 30 seconds of plugging everything in the motor is already very warm, without actually ever turning (ESC restarted itself again). My guess is there's some sort of motor short that is drawing a lot of current which is heating up the motor and...
  12. P

    ESC restarts itself?

    I recently finished my build and took it out for the first street-test. It ran fine for a couple minutes, and suddenly the ESC restarted itself. Now, even with no load, when I engage the throttle the motor will turn a revolution or two before the ESC restarts itself. The batteries are...
  13. P

    Screw-reinforced printed motor mount?

    I do have the ability to run stress tests, but frankly not sure what the right kinds of analyses would be. I feel like the real trouble would be fatigue-type issues?
  14. P

    KV vs Gearing?

    Tangential but related question. Mechanical power is Pmech = T x w Where t is torque and w is angular velocity, aka rpm. T = kt x I w = kv x V = V / kt Put it all together Pmech = kt x I x V / kt = I x V = I x I x R = copper losses Does that mean that our motors all waste half the power as heat?
  15. P

    Screw-reinforced printed motor mount?

    I am still building my first board so not yet. But if anyone has a 3d printer and can help me out, ill gladly pay for materials and document the process?
  16. P

    Screw-reinforced printed motor mount?

    3D printed motor mounts seem to be quite failure prone, but maybe we can reinforce them with metal bolts to make for a relatively cheap mount alternative? What do you think? I'm not really sure what the common modes of failure are, but maybe we can overcome the challenges. My gut says set...
  17. P

    KV vs Gearing?

    Ah, you're right, I messed up my math, the resistance for the low kv motor is 4x higher, not equal to that of the high kv motor. And since they both draw the same current per unit torque at the wheels, you want to use the highest kv motor practical.
  18. P

    KV vs Gearing?

    Ok, so I've done a lot of thinking about this and I'm pretty sure I got this figured out. Given two different setups: 1) 150 kv motor, geared 24:36 with 83mm wheels, 6s LiFePo, theoretical top speed of 19.2 mph 2) 300 kv motor, geared 12:36 with 83mm wheels, 6s LiFePo, theoreitcal top speed of...
  19. P

    Estimating accelerations?

    Hah good point. What do you mean by applied torque, and quantitatively, how is it related to speed?
  20. P

    Estimating accelerations?

    I'm trying to estimate acceleration times, and as long as my math is right hopefully it'll be helpful for others too. Someone mind helping me double check the physics? Question: how long does it take you to reach top speed if you weigh 200 lbs and are running a 6s LiPo setup with a Turnigy SK3...
  21. P

    KV vs Gearing?

    Ah, Vedder's analysis makes a lot of sense. Thanks!
  22. P

    KV vs Gearing?

    Is there any advantage to running a lower kv motors with a lower gear ratio (larger motor pulley) vs higher kv/higher gear ratio? I read that kv is also the motor torque constant (via some unit conversions, kv = N*m/A), and ran some numbers, and it looks like for a given board speed, it doesnt...
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