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  #46   Spotlight this post!  
Unread 25-06-2014, 09:17
Lil' Lavery Lil' Lavery is offline
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Re: Motors: Past and Future

Quote:
Originally Posted by Julian Gabriel View Post
Have any of you used the snowblower motor this year? I saw that it was added, but I hadn't heard much about it.
It's actually been around a couple years, but I have not used it.
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Unread 25-06-2014, 10:55
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Re: Motors: Past and Future

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Originally Posted by Lil' Lavery View Post
It's actually been around a couple years, but I have not used it.
Oh I hadn't realized, I had just assumed it was new. My bad. Anyway has anyone found a good use for it on their robot?
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Unread 26-06-2014, 08:23
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Re: Motors: Past and Future

It seems that many teams chose other motors since only one snowblower motor was allowed. I did inspect some robots with the motor, but I would put it in the less than 5% range.
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  #49   Spotlight this post!  
Unread 26-06-2014, 13:26
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Re: Motors: Past and Future

Snow blower motors. We all should clearly absolutely totally use those.
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Unread 21-11-2014, 23:31
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Re: Motors: Past and Future

First Post
Ok, so I have gone through the search for over 20 mins and have also read last years rules and I cannot find where it prohibits using a DC/DC converter to raise the voltage to 18vdc to run a RS-775-18 at 18vdc. Wouldn't this be covered under custom circuits?

Whether or not that would be advisable is a different question.

Thanks in advance for your patience
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Unread 21-11-2014, 23:39
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Re: Motors: Past and Future

Quote:
Originally Posted by Ragingmain View Post
First Post
Ok, so I have gone through the search for over 20 mins and have also read last years rules and I cannot find where it prohibits using a DC/DC converter to raise the voltage to 18vdc to run a RS-775-18 at 18vdc. Wouldn't this be covered under custom circuits?

Whether or not that would be advisable is a different question.

Thanks in advance for your patience
I don't know why this would even matter.

The PDB will only supply 40A (at 12 volts) to a motor, or the individual breaker will reset.

That means that only 480 electrical watts can run through your motor anyways.

Stepping up the voltage to 18V drops your maximum amperage to just 26.6 amps.

I haven't looked at the specific motor torque/rpm/current curves, but barring inefficiency, they can only operate at the same maximum power
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  #52   Spotlight this post!  
Unread 22-11-2014, 01:03
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Re: Motors: Past and Future

Quote:
Originally Posted by Al Skierkiewicz View Post
It seems that many teams chose other motors since only one snowblower motor was allowed. I did inspect some robots with the motor, but I would put it in the less than 5% range.
It's also a pain to mount/interface with, even moreso than the window motor (actually, I've gotten a lot of mileage out of the window motors in my time in FRC).
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  #53   Spotlight this post!  
Unread 22-11-2014, 08:37
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Re: Motors: Past and Future

Raging,
R53
CUSTOM CIRCUITS shall not directly alter the power pathways between the ROBOT battery, PD Board, motor
controllers, relays, motors, or other elements of the ROBOT control system (items explicitly mentioned in R64). Custom
high impedance voltage monitoring or low impedance current monitoring circuitry connected to the ROBOT’S electrical
system is acceptable, if the effect on the ROBOT outputs is inconsequential.
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  #54   Spotlight this post!  
Unread 22-11-2014, 10:12
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Re: Motors: Past and Future

Quote:
Originally Posted by BBray_T1296 View Post
I don't know why this would even matter.
It matters a lot. See below.

Quote:
The PDB will only supply 40A (at 12 volts) to a motor, or the individual breaker will reset.
The breaker doesn't reset instantaneously.


Quote:
Stepping up the voltage to 18V drops your maximum amperage to just 26.6 amps.

I haven't looked at the specific motor torque/rpm/current curves, but barring inefficiency, they can only operate at the same maximum power
The power you are referring to above is the input electrical power.

Operating at higher voltage makes the motor much more efficient. The output shaft mechanical power at 18 volts and 26.6 amps is much greater than the power at 12 volts and 40 amps.


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Unread 22-11-2014, 10:23
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Re: Motors: Past and Future

Quote:
Originally Posted by Ether View Post
Operating at higher voltage makes the motor much more efficient. The output shaft mechanical power at 18 volts and 26.6 amps is much greater than the power at 12 volts and 40 amps.
But what is the efficiency of the DC-DC converter and at what cost, considering the high current draw?
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Unread 22-11-2014, 10:34
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Re: Motors: Past and Future

Quote:
Originally Posted by Joe Ross View Post
But what is the efficiency of the DC-DC converter and at what cost, considering the high current draw?
That's a separate question (but a good one).

There's also the question of motor speed. To get the higher output mechanical power, the motor would be operating at a higher speed, thus (potentially, depending on the application) requiring another stage of gear reduction with the attendant additional inefficiency.

But the point is, the RS-775-18 was designed for 18 volts, and it is far more efficient at that higher voltage.



Attached Files
File Type: doc 775@18V.doc (22.0 KB, 23 views)
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Unread 22-11-2014, 16:32
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Re: Motors: Past and Future

Ether
Thank you for that document. That is exactly why I was thinking about this. V=IxR. So if the voltage increases the amps go down. Less heat, more efficient and as shown more power. But from reading the rules a bit closer it appears it is a no no. Thanks for all of your help
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Unread 22-11-2014, 17:56
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Re: Motors: Past and Future

Quote:
Originally Posted by Ragingmain View Post
Ether
Thank you for that document.
Here's a link to the app that created the output, in case you'd like to experiment with it.


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Unread 22-11-2014, 21:48
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Re: Motors: Past and Future

Quote:
Originally Posted by Ether View Post
It matters a lot. See below.

The breaker doesn't reset instantaneously.

The power you are referring to above is the input electrical power.

Operating at higher voltage makes the motor much more efficient. The output shaft mechanical power at 18 volts and 26.6 amps is much greater than the power at 12 volts and 40 amps.


The number crunching began, and then I discovered that the 775-12 stalls at 30 Amps anyways, so a clear victory to the -18

I concur that there is plenty of leeway in the breakers before they pop.
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Unread 23-11-2014, 00:10
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Re: Motors: Past and Future

So why allow an 18v motor if we can't effectively use it???
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