Motor RPM throttling problem

Discussion in 'First Build' started by Steven.H, Jul 13, 2018.

  1. Steven.H

    Steven.H New Member

    I'm building a video quad. This is my first build. I've got a couple of others that I've bought ready to fly.

    I've got a set of T-Motor MN3110 KV470 motors for this build. I've been trying different props with this. Started off with some 10 x 3.3 CF from TMotor as well, those work fine, and I get the expected thrust based on the datasheet on Tiger Motors page:
    ... apparently I can't post links until I've made 3 posts... look up tiger motors home page then search on their page for MN3110 and select the 470 KV motor.
    Was using a 6S battery with that propeller.

    However, when I tallied my total drone weight I realized the 10 inch prop just wasn't really going to cut it. While it would work and maintain right at the recommended 2:1 thrust weight ratio, the flight time was going to be lower than I desired. My goal is a theoretical 30 minute hover time as like I said this is for a video drone so I want to get a good amount of time in the air for recording. With the 10 inch props and my drones total weight at around 2100 grams with battery, that was going put me closer to 20 minutes.

    So, I decided to bump up the frame and prop size. I had started with a 500 frame, found a 650 frame and decided to give the 15 inch props a go as they should have the most efficiency for the lift required according to the T-Motor specs. I'm using a 4S battery in this configuration. This is when I started having problems. The motor starts to spin, but the just throttles at a really low RPM. The watt meter I'm using to monitor amp usage on my little test bench is barely registering any amperage draw. But the motor refuses to spin any faster. Every now and then I can get it to spin to full speed, but I have not been able to determine what is different when it does. And it can be infuriating that it'll spin up to full speed one time and then if I lower the controller back down and try to speed up again it throttles RPMs again. I've tried swapping batteries, escs, and the motor itself and the issue repeats.

    Here is a video of what it's doing:
    ...again apparently I can't post links. It's at youtube /watch?v=mcEKsXYpPXU to the end of the url.

    Anyone got any idea what is going on here? The motor does this from sitting for hours, so I don't think it's an overheating motor. Same for the ESC, I don't think it's overheating. If it were I would think that it would still have issues ramping up the RPM after taking the propeller off immediately after having it throttle RPM, but it doesn't. I also would think if it was a heat issue it'd at least build up more speed before showing signs of issues. The battery has plenty of charge, voltage around 15.8 volts during testing. I was wondering if the arduino I'm using to control the ESC on my test bench might be the problem but that doesn't seem likely either because if it were it would also have problems with no propeller or a 10" propeller as well.

    Really hoping someone can help me figure this out. I'd like to make progress on this drone, and I've already thrown to much money at it buying different propellers and frames and such trying to get a setup that works lol.
     
  2. Jackson

    Jackson USA member at large

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