Electric Vehicle C

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Electric Vehicle C

Postby robotman » August 22nd, 2015, 2:39 pm

Discussion for Electric Vehicle C.

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Re: Electric Vehicle C

Postby windu34 » August 31st, 2015, 4:33 pm

What brand or style of brushless motors would be the best for this event?
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Re: Electric Vehicle C

Postby iwonder » September 1st, 2015, 5:14 am

windu34 wrote: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.
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Re: Electric Vehicle C

Postby retired1 » September 2nd, 2015, 3:22 pm

Considering that there is not a significant weight problem, what advantage would a brushless motor have over a less expensive brushed motor?

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Re: Electric Vehicle C

Postby windu34 » September 2nd, 2015, 7:40 pm

Speed, Torque, integratability to a microcontroller
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Re: Electric Vehicle C

Postby Flavorflav » September 4th, 2015, 7:48 am

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.

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Re: Electric Vehicle C

Postby JonB » September 4th, 2015, 9:31 am

Flavorflav wrote: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).

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Re: Electric Vehicle C

Postby iwonder » September 4th, 2015, 7:30 pm

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.
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Re: Electric Vehicle C

Postby windu34 » September 4th, 2015, 8:16 pm

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.
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Re: Electric Vehicle C

Postby iwonder » September 4th, 2015, 8:40 pm

windu34 wrote: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]
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Re: Electric Vehicle C

Postby windu34 » September 5th, 2015, 11:24 am

Regardless, it will be interesting to see which direction teams decide to take whether it be fast motors with creative breaks or precise motors with creative speed increasing (gearing).
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Re: Electric Vehicle C

Postby retired1 » September 7th, 2015, 1:48 pm

If you are using a stepper motor it will need to be geared so that the driven tires do not spin.
I seriously doubt if many teams will get to sub centimeter accuracy. Everybody should be able to get to under 5 cm which is going to make speed very important since time is multiplied by 10.
It would be nice if all states had photogate timing because 3 people can rarely time within 0.1 seconds of each other.

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Re: Electric Vehicle C

Postby windu34 » September 7th, 2015, 3:03 pm

The time problem was a huge problem during the 2008-2009 season which is probably way they changed the event from predicting a time to just going as fast as possible because at the regional and state level, there shouldn't be too many people with really good time and at the nats level, there will be a photogate system so it won't be a problem.
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Re: Electric Vehicle C

Postby Flavorflav » September 10th, 2015, 11:04 am

JonB wrote:
Flavorflav wrote: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).

Well, there goes my credibility! I was expecting to see |predicted-actual|/actual again. This makes for a very different event.

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Re: Electric Vehicle C

Postby windu34 » September 10th, 2015, 3:01 pm

Yeah I was expecting that too, I even built a perfect vehicle over the summer with stepper motors for extreme precision. Back to square one.
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