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-   -   HH Cobalt Puller- Reborn page 35! (http://www.rccrawler.com/forum/holmes-hobbies/86181-hh-cobalt-puller-reborn-page-35-a.html)

svt923 03-16-2018 02:18 PM

Re: HH Cobalt Puller- Reborn page 35!
I ordered my 16T as soon as I saw them hit the site a day or 2 ago. "thumbsup"

Out of curiosity, what tradeoffs do the magnum design make compared to the regular Crawlmaster? Price is an obvious one and I would guess increased amp draw as well but are there others?

JohnRobHolmes 03-16-2018 03:30 PM

Re: HH Cobalt Puller- Reborn page 35!
Slightly higher no-load losses is the performance tradeoff to gain the torque and smoother startup. Otherwise it is all upsides.

Voodoobrew 08-24-2018 07:45 PM

Re: HH Cobalt Puller- Reborn page 35!
what are no load losses?

JohnRobHolmes 08-25-2018 06:59 AM

Re: HH Cobalt Puller- Reborn page 35!
Amp draw when the motor is not doing work

Voodoobrew 08-26-2018 12:09 AM

Re: HH Cobalt Puller- Reborn page 35!
In practical terms what are the effects of this?
Higher load losses mostly cause more motor heat and shorter run times?

JohnRobHolmes 08-27-2018 08:38 AM

Re: HH Cobalt Puller- Reborn page 35!
yep, slightly more heat and lower runtimes. The runtime change depends on the average load, which in an average crawler is on the order of a few amps (2200mah battery lasting an hour). If you are burning 5ah per hour or in 15 minutes, it wouldn't be nearly as noticeable to add 0.2a more losses as compared to 2.2a per hour discharge rate.

The same can be said for any "upsizing" of active motor materials. A Puller stubby (17mm long rotor) has lower no load than a standard (26mm long rotor), which has lower no load than an XL (36mm long rotor). The smallest motor will produce the least amount of power and torque, but net the longer runtime if the average amp draw (load) is low where a sizable portion is made up of no-load loss. Same example of 2.2 amp hour discharge rate, the stubby will have the longest runtime all else equal. Go to a faster rig like a U4 race, and the average load is far higher, which puts no load losses as a smaller fraction as compared to copper losses, in which case the standard or XL might give longer runtimes because they can handle a higher load at a higher efficiency point.

The take home of this, is that it is always a balance to find a motor with "enough" torque for the tough spots without impacting efficiency at really low loads. The monkey wrench is the human variable. When people upsize a motor, they typically use the extra torque too, so maybe runtime goes down or maybe it is unchanged because the efficiency boost under peak load is higher than the smaller motor.

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