Re: Motors: Past and Future
 

It's actually been around a couple years, but I have not used it.

Re: Motors: Past and Future
 

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?

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.

Re: Motors: Past and Future
 

Snow blower motors. We all should clearly absolutely totally use those.

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 ;)

Re: Motors: Past and Future
 

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

Re: Motors: Past and Future
 

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).

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.

Re: Motors: Past and Future
 

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.

Re: Motors: Past and Future
 

But what is the efficiency of the DC-DC converter and at what cost, considering the high current draw?

Re: Motors: Past and Future
 

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.

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:)

Re: Motors: Past and Future
 

Here's a link to the app that created the output, in case you'd like to experiment with it.

Re: Motors: Past and Future
 

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.

Re: Motors: Past and Future
 

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