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InstaSpin questions


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Hi All,

 

***I just answered my own question... InstaSpin isn't for use with hall sensors.***

 

I have a little commission in working on and am wanting to use an MSP430 in it.

 

My customer wants and extremely simple BLDC controller to drive a Maxon EC 90 Flat BLDC motor in a farming application.

 

The functionality will be very simple. Power comes on, motor ramps up to 500RPM and stays there. The motor has hall sensors which I will use to keep the speed constant under load.

 

Power turns off, motor coasts to a stop.

 

Is InstaSpin capable of such a simple task or is it more designed for advanced motion control? This is an ongoing requirement so I want to be able to program the MSP430 once and not have to configure each and every one of them (happy to calibrate the first one of course).

 

Thanks in advance.

 

Alec

 

 

 

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Hi Alec, seems to me that of your motor has hall sensors, use them! You will get much better reliability than a sensor less algorithm. They also help with speed. I have a pretty old project called BLDC booster for MSP430g2553 that you can check out of git hub: https://github.com/lgbeno/BLDC-Booster. Don't get me wrong instaspin is cool be no need making if more difficult on yourself...

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Hi Alec, seems to me that of your motor has hall sensors, use them! You will get much better reliability than a sensor less algorithm. They also help with speed. I have a pretty old project called BLDC booster for MSP430g2553 that you can check out of git hub: https://github.com/lgbeno/BLDC-Booster. Don't get me wrong instaspin is cool be no need making if more difficult on yourself...

Hi there! Totally agree, see my edit at the top of the post :)

 

I have bookmarked your project. Super useful thanks! I'll likely have a few questions but that answers a few of them :)

 

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What is really funny is that I did my testing on the same Maxon Motor!ne3uhavu.jpg

 

Oh nice haha. This is a bit off the subject of the original thread, but seeing as it was pointless anyway ill ask anyway :)

 

My customer is using the 48V version on a farming truck (4 of them). How do you think the components you have chosen would last in an industrial situation with lots of vibrations etc?

Reliability is the key for my customer so i'm wanting to keep operating temperature down and over spec the FET's. 

 

I was planning on using FETs and a FAN7388 driver IC, but it looks like you used NPN transistors??

EDIT: Just noticed your PRO version used a FAN7888 which must be similar :) They say imitation is the highest form of flattery...prepare to be flattered :) *With credit given of course!*

 

I was also considering operating the PWM at 55kHz as that is what the Maxon ESCON 36/3 controller operates at. How did you find the lower frequency you have chosen operates?

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My primary goal was to generate the lowest possible BOM cost for the board so that is why I went with discrete transistors.  For a real product like you are suggesting, a proper driver chip is absolutely the right way to go.

 

FAN7388 looks like an awesome part, it is also very inexpensive compared to other solutions from TI or Allegro.  I never did build to pro but thought that it would be much better from a efficiency point of view.  Using High side NMOS is also a big improvement which FAN7388 enables.

 

I think you're on the right track for reliability, keep the solution as cool as possible.  It can be a little bit of a delicate balance when specing MOSFETs because RDSon and Gate Capacitance work opposite of one another.  So higher gate capacitance means inefficiencies in the driver vs Higher RDSon means losses in the switch.  It is however easier to get the heat out of a FET.

 

About the PWM frequency, I think that I was using ~20kHz, it worked fine, at first we were doing 10kHz and there was some audible sound coming from the motor, I still found some noise but we thought that it was related to the commutation of the motor, that should be better if you actually have a load and also it's a farming truck so it probably is not a quiet environment...  Thinking about the timer clocks for MSP430 to know what PWM duty cycle resolution that you could get with a higher frequency.  16MHz=62.5ns 55kHz=18180ns so thats about 290 clock cycles meaning that you have about 8bits resolution and a step size of 0.34% not too bad...  Just remember that switching losses go up as frequency increases.

 

The design is open source so use away!  It would be great if you fed some of the code back to the community, understand if you can't though.

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There is nothing particularly secret about this project. I'm in sales, but I have a customer who is somewhat lacking in electrical knowledge ask me to create a small BLDC controller for him so he doesn't have to use the awesome, but massively over-speced (for his application) controller from Maxon. This wont be commercialised beyond that so happy to contribute where I can.

 

I am a bit of a novice, and really only know enough to adapt what I read online from projects like yours so hopefully I can add something.

 

I planned to use the MSP430G2452 to keep the size down*, but I hadn't thought about using timers to measure the speed from the hall sensors! Might as well keep it simple and use what you've made available.

 

* I have a goal to keep it below 25mm x 50mm. I have been given a very limited space in a sealed enclosure, right behind the motor. Fertilizer does nasty things to electronics, so we are trying to keep everything together in one compact unit to avoid unnecessary connectors.

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G2452 should work, G2412 would be ok if you don't have a use for an ADC, which it sounds like you do not.

 

Using a timer for speed detect is more of a nice to have than anything. For the simplicity of this design, you can just use the one timer and CPU and get fine accuracy.

 

How many of these things are you making?

Edited by Lgbeno
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G2452 should work, G2412 would be ok if you don't have a use for an ADC, which it sounds like you do not.

 

Using a timer for speed detect is more of a nice to have than anything. For the simplicity of this design, you can just use the one timer and CPU and get fine accuracy.

 

How many of these things are you making?

 

About 100 per year is an estimate. I'm in New Zealand, so our volumes aren't quite as high as most other countries!

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