Thinking about dyno's for brushed motors

[coxbros1]

those #'s sound right. I had 15x2 turn 32,2xx recently on 7.2.v. watch out turning those 12 turns too fast on free rev....i have had the winds snap

[Coelacanth]

Awesome...I wonder how fast a brushed 540-sized motor can spin, theoretically, before it's at risk of grenading? There has to be a limit or else brushless wouldn't have been invented.

[coxbros1]

yup....it was a Reedy 12×2. I had it on that Trinity Motor Machine back in the day. (loved that machine, should never have sold it) It was going over 40k then SNAP!. It broke one of the windings going to the comm best i can remember. I think they are relatively safe if u keep em below 40k

[juicedcoupe]

I don't know how fast it was turning on 7 cells, but it was screaming. I thought I seen it flash 60 something and then error.

[Frankentruck]

I haven't hooked up a voltmeter yet and don't have an ammeter, but gave some of the motors a trial run on a freshly charged 6 cell pack. The Trinity X-Star stock motor was in the mid 28k RPMs, the CAM modified was an almost identical 28k RPMs, a brown label Associated was 24k RPMs, and what I think is a Black Magic marine motor was 22k RPMs. I've only run the X-Star and CAM in a vehicle so far, but with same 96T / 18T gearing the CAM was significantly faster acceleration and top end. No load RPMs are leaving some important details out, so will ponder the next setup evolution a bit.

[jeekelemental]

Great topic, very useful. I'm always in doubt with my old motors or with the used I refurb and pretty desperate because dynos are going rare and expansive. I will take inspiration to build my own dyno, thanks for sharing.

[Dadio]

The thing I've found is my motors run cooler after adjusting the timing for a lower amp draw and the performance is not hugely effected compared to the longer run times before it gets hot .

[Frankentruck]

I picked up some Dymond motor setups that are supposed to include a blank armature to wind yourself. One already had been wound. It isn't balanced, but puts out a respectable 40k rpm on a 6 cell pack. I put a Trinity speed gems 11 triple armature in another. It ran up to 45k rpm. I need to source some wire for my own custom armatures, but haven't decided what gage to use.

I also have one motor that keeps burning up brush springs. The last one was on the positive side. The tang that contacts the brush is turning blue and deforming. I'm not sure if it's a brush or endbell issue.

[Frankentruck]

I think I need a flex coupling of some sort, like a tiny Rexnord that has a floating damper.

[coxbros1]

Nice setup!

[Dadio]

That does look good , you might be able to link up the motors with a short section of rubber tube as a flexi joint at some point on the shaft ?

[Frankentruck]

I'm thinking about incorporating an extra 2.6 ratio gearbox with an outdrive and dogbone that connect to the load motor. But if I only connect to one outdrive, the ball diff might just spin the other unloaded outdrive. I'd like the diff to basically be locked, but I don't think I should just super tighten the tension bolt. That doesn't seem like a good thing to do to parts that might go into a truck in the future. At least I'm not quite committed to locking it up yet, and I need to get a sacrificial dogbone. Maybe a 6 gear would be a better gearbox choice. Hmmm....

[juicedcoupe]

I'm thinking about incorporating an extra 2.6 ratio gearbox with an outdrive and dogbone that connect to the load motor. But if I only connect to one outdrive, the ball diff might just spin the other unloaded outdrive. I'd like the diff to basically be locked, but I don't think I should just super tighten the tension bolt. That doesn't seem like a good thing to do to parts that might go into a truck in the future. At least I'm not quite committed to locking it up yet, and I need to get a sacrificial dogbone. Maybe a 6 gear would be a better gearbox choice. Hmmm....

The diff in a six gear works the same way.

And, don't you dare! RC10 transmissions cost as much as some RTR's.

[Frankentruck]

Not that I've ever had a 6 gear, but isn't the diff the spur and balls setup that's on the outside? Tightening that to lock the diff seems like it just involves a generic spur gear setup.

[juicedcoupe]

Yeah, the spur gear is generic. But potentially trashing a diff tube or outer hub doesn't seem like a good idea.