Motor, Battery and Control Selection for Kids Race Challenge

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BlueBell
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Motor, Battery and Control Selection for Kids Race Challenge

Post by BlueBell » Nov 05, 2017 7:22 pm

Looking primarily for some motor recommendations for our entry into the SMUD Solar Challenge next May in California.
We are given (loaned) four, used MSX-64 solar panels putting out about 300 watts at best.
We are allowed 180 watt-hours in a sealed marine battery.
Our hull speed is about 6 MPH and we have a selection of model airplane propellers to test which is optimum under two different conditions: solar panels only and battery only.
For the battery only section, we need to travel as far as possible in 25 minutes. If we run out of juice before 25 minutes, we are disqualified!
For the other two events, we can use panels only.
Propeller changes are allowed between events.
No motor or battery changes are allowed.

We need to purchase a motor, controller, solar-charger, 180 watt-hour maximum battery, kill switch (on a lanyard), momentary fwd/rvs switch (dead-man-throttle), and a 3-way power switch.

The poorly worded rules are found here:
https://www.smud.org/assets/documents/p ... packet.pdf
Pages 17, and 22 - 25 are of special interest here.

We have great advice and mentorship on everything but the above mentioned items.
That's why we're here, on this forum looking for suggestions, help, or recommendations.
The lower the RPM and higher the propeller diameter the better.
Gearing would be a challenge and no where near as simple as a four foot shaft straight off the swivel mounted motor on the aft deck, like a long-boat in Thailand.

Thanking you in advance.
Last edited by BlueBell on Nov 08, 2017 3:27 pm, edited 5 times in total.

BlueBell
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Re: Motor, Battery and Control Selection for Kids Race Chall

Post by BlueBell » Nov 08, 2017 3:19 pm

I have learned wattage is more like 250 from the four used solar panels combined.

Is there a better place for me to put this thread?

It's for a kids scout project. Maybe I should have put that in the title!

BlueBell
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Re: Motor, Battery and Control Selection for Kids Race Chall

Post by BlueBell » Nov 11, 2017 11:37 am

Okay, looks like we're leaning towards a 6:1 internally geared brushless motor (https://www.aliexpress.com/store/produc ... 80679.html to give us our 500 RPM propeller speed.
Comes with a controller.
With a 13s, 2p lipo for the 25 minute endurance heat.
A digital volt/amp meter will allow the pilot to maintain a >30V throttle setting via a HALL twist grip on the end of one of the steering sticks.
What charger could we put between the battery and the panels?

Does all this sound reasonable?
Thanks.

BlueBell
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Re: Motor, Battery and Control Selection for Kids Race Chall

Post by BlueBell » Nov 14, 2017 2:44 pm

We've switched our proposed battery to four of these in series in an effort to keep the voltage down through the charger:
https://hobbyking.com/en_us/turnigy-bat ... xt-60.html
Would you like to comment before we go ahead and order these along with the motor: https://www.aliexpress.com/store/produc ... 80679.html
And charger: iMax B6 https://www.ebay.com/sch/i.html?_from=R ... 5573.m1684

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fechter
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Re: Motor, Battery and Control Selection for Kids Race Chall

Post by fechter » Nov 14, 2017 2:57 pm

The internally geared motor is a good idea. I don't think you could get a good match to the propeller with direct drive.
The Lipo batteries will handle the load easily. Just be real careful when charging and don't drop them. Some kind of protective case (plastic ammo box?) might be a good idea.

Getting the motor to run off panels only might be tricky. There will be a tendency for the motor to draw a bit too much on startup and trigger the low voltage cutoff on the controller. A really big capacitor across the controller power input might help. Once you get it going, it should be OK.

Where do they run the race?
"One test is worth a thousand opinions"

BlueBell
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Re: Motor, Battery and Control Selection for Kids Race Chall

Post by BlueBell » Nov 14, 2017 5:13 pm

Thanks Fechter.

The battery will be mounted in the boat.
So long as we don't drop the boat, we should be okay.

The race is held in California in May.

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fechter
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Re: Motor, Battery and Control Selection for Kids Race Chall

Post by fechter » Nov 14, 2017 11:24 pm

Where in California? I might want to watch.
"One test is worth a thousand opinions"

BlueBell
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Re: Motor, Battery and Control Selection for Kids Race Chall

Post by BlueBell » Nov 15, 2017 12:28 am

Sacramento.
Check out the original post on this thread.
See you there?

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fechter
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Re: Motor, Battery and Control Selection for Kids Race Chall

Post by fechter » Nov 15, 2017 9:20 am

OK. Not so close, but who knows?
"One test is worth a thousand opinions"

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