How fast does the motor have to change direction?

Hi All,

I am wanting to build my own 2 or 3DOF sim, however I want to take a different approach and go with geared brushless DC motor. I have successfully got the brushless speed controller to go both direction and need to know if this is fast enough? Being in RC world for a while, I know rc servo are super fast, but I am not sure how fast does the motion servo need to be?

Here's a short video demonstrate how fast it can switch direction, however this is me turning the potentiometer back and forth as fast as I can, I am not sure whether it can be any faster with Adruino doing it. Advise?

No, I am not planning to use this tiny motor to power the system... if this work I will go with something a lot bigger running on 26volts.

FYI, there's a lot of slop in the gear drive.... might need to do something about that.

Well, my link doesn't seem to show up... because I need 5 post?

If you go brushless, then I recommend you to find a motor with a position sensor (you may know that from RC cars) since it will consequently reduce the power needed when changing direction or when starting the motor from a stop. Note that it would also reduce the lag in the same conditions.

I'm not convinced brushless is a better solution for our application but who knows? Just remember that a brushless motor uses a very, very big amount of power when starting/changing direction so you will probably have to oversize the controller.

Thank you for your reply. RC car motor are sensored motor. I am not sure if this is necessary, most of them tend to have a long pause built in between direction change. I think it have to decelerate and accelerate. However the speed controller I am using almost instantly go the other direction. RC car sensored esc are expensive, I am trying to use the cheap and power RC sensorless motor.

My main question is, does that direction changes fast enough? Anyone ?

It's hard to judge on a video but it seems to change direction quite fast. If that's your only concern, just give it a try.
I'm curious, have you measured the intensity passing through when changing direction like on your video and compared it to a full speed use?

I am not sure I know what you mean by measured the intensity passing. How would you measure that?

Ok, according to video editor, it take 2 frames for the motor to change direction, video was recording at 30fps.... does that mean 200ms to change rotation?

Sorry, my english is far from perfect I know by experience with RC products that the current (Amps) can heavily increase when starting a brushless motor from a stop (and so it will when changing direction). In fact, it's something we avoid in the RC world (or add capacitor on RC car motor controller). This peak can easily be 4 or 5 times higher than the nominal consumption, from what I've experienced.

My question was: did you measure the current consumed by your motor when changing direction like at the end of your video?

Beside this, I'm impressed by how fast it actually change direction

Ok. Here's some test result.

12volts
full power, no load pull .19amp
full power one direction, then change to reverse direction full power pull 5amps

My speed controller is rated 40amps constant and 60amps burst. So it isn't a issue for the speed controller yet... But that big of a surge of amperage is a big problem even at 66ms? (this is my calculation if it was 2fps).

Strange results, the peak is maybe to short to be seen. Again, I don't know specifically the kind of controller you are using and I'm just referring to what I know from RC project (and small, but scale 1, 3 wheels cars as well )

To be honest, when I see how fast is reacting your motor, my only concern would be the current peak. Otherwise, brushless motors are far more efficient and also full of torque

Can you tell us more about the type of motor you plan to use (power, kv and dimensions)? What about gearbox ratio?

hello!

you need speed under load
so you have to deal with power rather than only speed

yes arduino will be faster...
and it can easily ask more than the motor or power supply can give

If the back and worth are too quick : it can generate such high peaks that the PSU shut off

If they do something like this under load, you are about spot on

Or this, comes alive at 46 seconds

Thanks guys. I guess just have to try it and see. Since the controller can run on 26volts, I'm hoping when I switch to higher voltage it will drop the amp draw a bit.

Sorry to bother everyone again. But got a few more question.

1. I see most people are using the MM Dual H bridge controller, does this receive PWM signal?
2. I see there's Ardruino code to control RC servo directly, but these rc servo already have the pot inside the servo. But I would need to connect my pot directly into the Ardruino and run PWM signal to my RC speed controller.

Are there such written code for Ardruino already?

thanks

Hi. The answer to question 1 is yes. The answer to question 2 is since the answer to question 1 was yes, the standard h-bridge sketches available here output pwm. I couldn’t say if any of them are compatible “out of the box” with what your Rc controllers expect though since I don’t use either myself.

Btw. While no load tests are easy to set up and get some initial results, the only ones that count are full load tests to see if everything has what it takes. Good luck with it!

Thank you, if it's pwm, then should work...

@helisfreak , please keep us posted with your tests and the hardware used

no, it's not driven in the same way
Arduino RC servo code and pot + wiper code are different..

look in the Resources for arduino code "Download" menu http://www.xsimulator.net/community/marketplace/categories/firmware-for-interfaces.31/
or FAQ http://www.xsimulator.net/community/faq/arduino.6/category