MagLev C

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Re: MagLev C

Post by illusionist » December 4th, 2012, 1:06 pm

Is it possible to calculate how much thrust is required from my motor/propeller without worrying too much about friction and aerodynamics of the maglev vehicle?
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Re: MagLev C

Post by Balsa Man » December 4th, 2012, 2:12 pm

illusionist wrote:Is it possible to calculate how much thrust is required from my motor/propeller without worrying too much about friction and aerodynamics of the maglev vehicle?
It's not really a question of how much thrust is "required"- if you do a decent build, friction will be pretty low, and with pretty minimal thrust - a small, cheap motor and a pretty small prop, it will make it all the way down the track. So, in some way, I guess, the required thrust is enough to do that. The question- the design challenge - is how fast you can get it down the track. With enough thrust to just get it from one end to the other, you might be looking at....3, 4, 5...6...7 seconds.
Back on the previous page, I threw out a way to roughly calculate that, and to compare the thrust you can get from various motor/prop combos- measure the thust on a scale- that's your force for an F = ma calculation. You want mass right at the minimum; with as much thrust as you can get w/o going over the minimum. Good time for a meter should be on the order of a second....I think.
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Re: MagLev C

Post by iwonder » December 4th, 2012, 3:24 pm

I guess this hasn't come up, but I've never done this event before and I was wondering if there's ever any damage to propellers or motors and batteries with a sudden stop upon running into the cushioned barrier. Seems to me that the propellers would stop and the motors would stall... seems fairly destructive, is there some method that I'm missing for stopping this?
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Re: MagLev C

Post by Balsa Man » December 4th, 2012, 3:29 pm

iwonder wrote:I guess this hasn't come up, but I've never done this event before and I was wondering if there's ever any damage to propellers or motors and batteries with a sudden stop upon running into the cushioned barrier. Seems to me that the propellers would stop and the motors would stall... seems fairly destructive, is there some method that I'm missing for stopping this?
One way is to put a switch on the front of the vehicle, and a bar across the track (after finish line)- position things so switch hits the bar, and turns the switch/motor off. You can get button switches, where the first time you click it, it turns on, the next time it turns off
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Re: MagLev C

Post by harryk » December 4th, 2012, 3:39 pm

iwonder wrote:I guess this hasn't come up, but I've never done this event before and I was wondering if there's ever any damage to propellers or motors and batteries with a sudden stop upon running into the cushioned barrier. Seems to me that the propellers would stop and the motors would stall... seems fairly destructive, is there some method that I'm missing for stopping this?
That would only be a problem if your prop was on the front of the vehicle. Though you could still have something that sticks out further than the prop so that the prop never makes contact with anything, which is probably a good idea regardless.
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Re: MagLev C

Post by Balsa Man » December 4th, 2012, 3:58 pm

This.....aspect actually brings up a safety question. With a decent motor and prop combo, you have a serious finger slicer. I say that from.....direct experience; not stitches, but a badly sliced knuckle.

Running the vehicle into any sort of cushion/catcher, where its stopped, but prop is still going, and then having to reach in, grab it, and turn a switch off/pull a wire loose, how ever you power it down is.....a high hazard operation; as inherently dangerous as anything going on in any of the building events; I'd argue the most hazardous.

An obvious way to reduce risk would to run a prop guard- a ring or hoop - outside the prop- like a thin carbon fiber rod. Problem is, the rules prohibit that, by saying nothing but the prop can extend outside the plane of the inside of the track side rails. I'm sure that prohibition has it's reasons, but I have to suspect the impact on safety got overlooked. With the requirement for serious eye protection (the only need for which that I can imagine being like for a prop coming apart), really strange that protection from the much higher risk of prop bite isn't encouraged- or even required. That's why we went to the switch approach- it powers itself down.

S-O, btw, has been really good over the years about considering safety, even to the point of erring to the safe side on rules and required protective measures.
Last edited by Balsa Man on December 5th, 2012, 4:10 am, edited 1 time in total.
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Re: MagLev C

Post by iwonder » December 4th, 2012, 4:02 pm

That's one of those obvious things I knew I had to be overlooking... thanks!

Last question for you guys... what's the normal motor to prop attachment method? Are most people able to just push them straight on? or is there some magic bushing for this?
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Re: MagLev C

Post by Balsa Man » December 5th, 2012, 4:04 am

iwonder wrote:That's one of those obvious things I knew I had to be overlooking... thanks!

Last question for you guys... what's the normal motor to prop attachment method? Are most people able to just push them straight on? or is there some magic bushing for this?
In our local Hobbytown store, in the RC airplane stuff, they have prop adaptors- machined out of aluminum. One end fits motor shaft (they have 2, 3, &4mm sizes), then there is a section that has like 3 stepped diameter sections. Prop comes with a couple different collar inserts. Last part is a threaded shaft, and a rounded cone shaped spinner/nut- it tightens down on the threaded shaft to hold the prop on. Works like a charm.
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Re: MagLev C

Post by iwonder » December 9th, 2012, 2:38 pm

Got the vehicle running for the conest yesterday... aside from throwing a prop and almost hitting the protor's face( :o ) the vehicle averaged 1 second for a 1m run in 2 trials(before contest... we didn't get to run after it threw the prop). I was wondering, is anybody using LiPo batteries for their maglev? I've got an 8.4v NiMH pack now, should I switch over? I'm wondering if it'd be worth it... The time would definitely be improved, but at the cost of weight...
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Re: MagLev C

Post by mrsteven » December 10th, 2012, 10:27 am

LiPO are generally lighter than the NiHM equivalent in my experience.
Just more expensive, look into R/C types on weight search criteria
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