## Search found 22 matches

Aug 29 2018 11:05am
Forum: E-Bike Technical
Topic: Kv * turns = constant?
Replies: 10
Views: 876

### Re: 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 though, I ...
Aug 29 2018 12:29am
Forum: E-Bike Technical
Topic: Kv * turns = constant?
Replies: 10
Views: 876

### Re: 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?
Aug 26 2018 11:52pm
Forum: E-Bike Technical
Topic: Kv * turns = constant?
Replies: 10
Views: 876

### 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 * motor_inter...
Aug 25 2018 12:13am
Forum: E-Bike Non-hub Motor Drives
Topic: RC motors, rated current and power?
Replies: 7
Views: 823

### Re: RC motors, rated current and power?

Gotcha, makes sense. Thanks guys!
Aug 24 2018 7:35pm
Forum: E-Bike Non-hub Motor Drives
Topic: RC motors, rated current and power?
Replies: 7
Views: 823

### Re: 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 appear t...
Aug 24 2018 1:53pm
Forum: E-Bike Non-hub Motor Drives
Topic: RC motors, rated current and power?
Replies: 7
Views: 823

### 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: Turns: 14...
Aug 15 2015 10:53am
Forum: Stand-up E-scooters and E-skateboards
Topic: Integrating Lipo Charger into E-Board
Replies: 10
Views: 1332

### Re: 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 a cell...
Aug 14 2015 9:34pm
Forum: Stand-up E-scooters and E-skateboards
Topic: ESC restarts itself?
Replies: 11
Views: 1571

### Re: 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 need a ...
Aug 12 2015 8:09pm
Forum: Stand-up E-scooters and E-skateboards
Topic: ESC restarts itself?
Replies: 11
Views: 1571

### Re: 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 channe...
Aug 11 2015 8:12pm
Forum: Stand-up E-scooters and E-skateboards
Topic: ESC restarts itself?
Replies: 11
Views: 1571

### Re: 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 unfortu...
Aug 08 2015 10:31am
Forum: Stand-up E-scooters and E-skateboards
Topic: ESC restarts itself?
Replies: 11
Views: 1571

### Re: 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 triggering s...
Aug 02 2015 4:35pm
Forum: Stand-up E-scooters and E-skateboards
Topic: ESC restarts itself?
Replies: 11
Views: 1571

### 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 charged, the L...
Jul 13 2015 8:29pm
Forum: Stand-up E-scooters and E-skateboards
Topic: Screw-reinforced printed motor mount?
Replies: 14
Views: 2097

### Re: 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?
Jul 12 2015 3:52pm
Forum: Stand-up E-scooters and E-skateboards
Topic: KV vs Gearing?
Replies: 46
Views: 5080

### Re: 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?
Jul 12 2015 3:43pm
Forum: Stand-up E-scooters and E-skateboards
Topic: Screw-reinforced printed motor mount?
Replies: 14
Views: 2097

### Re: 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?
Jul 12 2015 10:29am
Forum: Stand-up E-scooters and E-skateboards
Topic: Screw-reinforced printed motor mount?
Replies: 14
Views: 2097

### 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 screws are...
Jul 08 2015 5:32am
Forum: Stand-up E-scooters and E-skateboards
Topic: KV vs Gearing?
Replies: 46
Views: 5080

### Re: 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.
Jul 06 2015 8:14pm
Forum: Stand-up E-scooters and E-skateboards
Topic: KV vs Gearing?
Replies: 46
Views: 5080

### Re: 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 19.2 ...
Jun 30 2015 10:07pm
Forum: Stand-up E-scooters and E-skateboards
Topic: Estimating accelerations?
Replies: 4
Views: 588

### Re: Estimating accelerations?

Hah good point. What do you mean by applied torque, and quantitatively, how is it related to speed?
Jun 30 2015 7:28pm
Forum: Stand-up E-scooters and E-skateboards
Topic: Estimating accelerations?
Replies: 4
Views: 588

### 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 6374 ...
Jun 27 2015 10:56pm
Forum: Stand-up E-scooters and E-skateboards
Topic: KV vs Gearing?
Replies: 46
Views: 5080

### Re: KV vs Gearing?

Ah, Vedder's analysis makes a lot of sense. Thanks!
Jun 27 2015 11:11am
Forum: Stand-up E-scooters and E-skateboards
Topic: KV vs Gearing?
Replies: 46
Views: 5080

### 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 matte...