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Electric Vehicle C

Posted: August 22nd, 2015, 2:39 pm
by robotman
Discussion for Electric Vehicle C.

Resources:
2009 Thread
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Re: Electric Vehicle C

Posted: August 31st, 2015, 4:33 pm
by windu34
What brand or style of brushless motors would be the best for this event?

Re: Electric Vehicle C

Posted: September 1st, 2015, 5:14 am
by iwonder
What brand or style of brushless motors would be the best for this event?
Really everything here depends on the rules and what they're looking for out of the vehicle. Brushless motors may not be the best option, but we won't know until rules are published.

Re: Electric Vehicle C

Posted: September 2nd, 2015, 3:22 pm
by retired1
Considering that there is not a significant weight problem, what advantage would a brushless motor have over a less expensive brushed motor?

Re: Electric Vehicle C

Posted: September 2nd, 2015, 7:40 pm
by windu34
Speed, Torque, integratability to a microcontroller

Re: Electric Vehicle C

Posted: September 4th, 2015, 7:48 am
by Flavorflav
I strongly suspect speed and torque will not be very important in this event, but as iwonder said we won't really know anything until we see the rules.

Re: Electric Vehicle C

Posted: September 4th, 2015, 9:31 am
by JonB
I strongly suspect speed and torque will not be very important in this event, but as iwonder said we won't really know anything until we see the rules.

Rules are out. Speed is part of the score (time score). Basically, it's how they determined run time for scrambler.

I must say that I am really, really surprised there are not more restrictions in the rules (brushed vs brushless).

Re: Electric Vehicle C

Posted: September 4th, 2015, 7:30 pm
by iwonder
Just to throw this out there, I would personally find a nice high torque stepper motor for this event and focus on the motion control to allow it to hit the target.

Done properly, which will require a significant, but reasonable, amount of effort, I believe sub-centimeter positioning is pretty reasonable. With the right setup such a motor could also move fairly quickly.

Brushless motors are nice, but precise speed control isn't really their thing. They can spin fast but the hobby level ESCs aren't designed to maintain speed to within an RPM or two, so you'd need some sort of position feedback, and a closed loop control system.

Both systems are reasonable, the stepper is open loop, so no position feedback is required, which makes the software easier, but you have to worry about accelerating stepper motors (they have these ugly things called resonances, microstepping is a decent work around). The brushless motor is closed loop, which means some sort of feedback and perhaps something like a PID loop, and some trial and error to make it work right. I believe both systems could achieve similar position and speed at the upper end of competition.

The disclaimer is that I haven't gotten my rulebook yet so I don't know all of the details, just the general idea. Oh, and in case you couldn't tell, this is arguably my favorite event in the whole of scioly. Like ever.

Re: Electric Vehicle C

Posted: September 4th, 2015, 8:16 pm
by windu34
There are brushless motors that will go 60mph in less than a second. Correct me if Im im wrong, but stepper motors will not come even close to that. Granted, steppers are easier to get precise distance wise, but this set of rules does not favor purely perfect distance; high speeds are needed to do well at high levels of competition.

Re: Electric Vehicle C

Posted: September 4th, 2015, 8:40 pm
by iwonder
There are brushless motors that will go 60mph in less than a second. Correct me if Im im wrong, but stepper motors will not come even close to that. Granted, steppers are easier to get precise distance wise, but this set of rules does not favor purely perfect distance; high speeds are needed to do well at high levels of competition.
Uhhh... Motors spin, but mph is a linear speed, so that doesn't even make sense. Certainly, brushless motors can accelerate fast, but both types of motors put out maximum torque from a standstill.

Next, you're not going to get your vehicle to 60mph on the track. Sorry. That's a safety issue even if it were technically possible. There are plenty of other options that will go as fast as your vehicle allows that aren't brushless.

[rant]
Look, brushless motors are great, they work well in airplanes, quadcopters, cars, and lots of R/C hobby things. They did well in MagLev when they were allowed. But they're not the end all be all magic bullet to solve all your problems. There are specific needs for this event, you need to determine what they are and research options for motors, picking the one the data says will do best. Don't go with the most expensive or the one that everyone hypes. This is engineering, go with the data.

I'm not saying steppers are perfect, in fact, I said, "Both systems are reasonable", (certainly there are even more options out there as well) and I'm not sure which way I would go if I were still competing. But I would have to sit down and work out designs with each and see what would get me the better score. It's best to not be locked in to 'Brushless, Brushless, Brushless' simply because that's the most hyped technology.
[/rant]