Timeline for DC motors not spinning at same RPM?
Current License: CC BY-SA 3.0
17 events
| when toggle format | what | by | license | comment | |
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| Mar 30, 2016 at 17:22 | comment | added | WhatRoughBeast | @SMD01 - Welcome to the world of real engineering. First rule is Murphy's Law: "Whatever can go wrong, will." Second rule: "It's never as easy as you thought it would be." Third rule is Finagle's Law: "The perversity of the universe tends towards a maximum." Good luck on your project. | |
| Mar 30, 2016 at 17:17 | comment | added | SMD01 | @WhatRoughBeast Alright I managed to get two 9926A dual n-channel mosfets off a board by putting it in a toaster. I see why you didn't recommend SMD. I didn't really have the right mounting hardware and being pressed for time i had to use what was available to me. I ended up breaking 4 legs off one of them, which led to me having to dremel it to expose more metal, soldering hair width wires to each stub, and epoxying it as they break off with little force. Not a fun experience. At least it works and the motors spin as expectedly now. Thank you for your help! | |
| Mar 30, 2016 at 17:16 | comment | added | WhatRoughBeast | @ChrisStratton - +1 for "a size class dangerously large for experiments" | |
| Mar 30, 2016 at 17:11 | vote | accept | SMD01 | ||
| Mar 26, 2016 at 3:05 | comment | added | Chris Stratton | DMN2041L should be good for a quad up to 50 grams all up weight (a couple of amps per motor) if not more, while letting you keep the entire PCB assembly (excluding any GPS) in the 2-4 gram range. If you are carrying a GPS you must be flying outdoors and may want larger FETs for a larger vehicle. | |
| Mar 24, 2016 at 19:25 | comment | added | WhatRoughBeast | @SMD01 - Not remotely adequate. Has the same gain problems as the 2N2222, although the current capability is adequate. Remember that, when you use a BJT as a switch, the rule of thumb is to assume a gain of 10. And this package is not a whole lot smaller than the TO220 of the PHP. If the weight of the PHP is an issue, you'll need to go to surface-mount devices. | |
| Mar 24, 2016 at 19:21 | comment | added | SMD01 | @WhatRoughBeast What are your thoughts on using this if the mosfets don't work (due to size/weight limitations) BD135 - fairchildsemi.com/datasheets/BD/BD135.pdf | |
| Mar 24, 2016 at 15:56 | comment | added | SMD01 | This project is part of my mechanical engineering degree so I can't abandon it! I only included a schematic for the motors but in reality it has an MPU-9250, 4 IR distance sensors, an ultrasonic distance sensor, and a GPS. So far, this has amounted to 40g being added to our quad, whose max thrust was initially 130g. Programming and flight mechanics I have ample experience with, the electrical aspect of it, not so much. | |
| Mar 23, 2016 at 15:40 | comment | added | Chris Stratton | If soldering an sot23 mosfet is a dealbreaker, the project should probably be abandoned. Getting something to actually fly will be far, far more complicated than the poster imagines, especially on the software side. They'll probably need to spend some time with existing boards and source code first, and until a size class dangerously large for experiments, those are surface mount. | |
| Mar 23, 2016 at 14:56 | comment | added | WhatRoughBeast | @jms - How experienced are you? Do you think the poster is in your league? Why? | |
| Mar 23, 2016 at 14:05 | comment | added | jms | The PHP79NQ08LT is certainly is a nice part to have in your component box for prototyping and general messing about, but OP specifically wrote that the thing is supposed to lift itself off the ground. A quadcopter powered by 4 coreless DC motors will certainly suffer from 8 g of extra weight from bulky TO-220 packages. While SMD parts, SOT-23 packages are still quite benign from a soldering perspective. | |
| Mar 23, 2016 at 13:49 | comment | added | WhatRoughBeast | @jms - If you go to the Digikey page and search for 2-volt Vgs MOSFETs, the PHPs are the lowest cost, through-hole units in stock with current of 1 amp or more. The OP does not seem at all experienced, and I'd hate to recommend a SMD to a beginner. | |
| Mar 23, 2016 at 3:40 | comment | added | Chris Stratton | Sot-23 Mosfets are typically suited for small quads up to a few amps. See rcgroups for specific part recommendations. | |
| Mar 23, 2016 at 1:28 | comment | added | jms | Rated 75 V and 73 A, the PHP79NQ08LT is overkill in every respect, why would you introduce it as the "best candidate"? The little quadcopter would have to lift 4 heavy TO-220 packages. A 1N4001 is not optimal either, as they are designed primarily for rectifying mains frequency AC and have a poor transient response and reverse recovery time as a result. | |
| Mar 22, 2016 at 21:22 | comment | added | WhatRoughBeast | @SMD01 - Go to digikey.com and search on discrete semiconductors, MOSFETs, and search for Vgs of 2 volts. The best candidate I see is PHP79NQ08LT, which will run you about 1 1/2 bucks each. And other than that, I don't see any problems with your circuit, except that you should put a flyback diode across each motor. A 1N4001 is probably adequate. | |
| Mar 22, 2016 at 19:45 | comment | added | SMD01 | Excellent! I'll try this as soon as I can! Would you recommend anything else? Different resistors maybe? | |
| Mar 22, 2016 at 19:22 | history | answered | WhatRoughBeast | CC BY-SA 3.0 |