Thinking about dyno's for brushed motors

[Dadio]

Interesting point , of course it would make no difference to the kyoisho 240 , 360 ... Numbering system that was based on seconds of run like on a 1200 mahr battery or so I think ? Could be wrong .

[Coelacanth]

You're right, actually...but there are images of their motors with comparable RPM ratings like this one...sometimes makes me wonder if they were all rated with the same input voltage. Kyosho wouldn't seem to me to be the kind of company to fudge their numbers.

EDIT: I just re-read the whole brochure and it mentions that they tested all these RPMs with 6-cell packs.

[coxbros1]

Great chart u posted! forget rpm, look what it says about the 480Gold!...its true too! thing rips!

[TheDiamondOne]

Coelacanth awsome pic and chart. This is exactly why lemans motors are by far the most classic best looking ever. Yeah there were faster motors, but these are legendary. Derek and me have done all that rpm dyno testing and its fun, but in my opinion, after actually testing all motors in same car, the results are just a number and deceiving. The best test is simply reading kyoshos description, its pretty darn accurate cuz that 480g whipped the crap out of the 240sb in the salute! 480GOLD4LIFE!

[juicedcoupe]

EDIT: I just re-read the whole brochure and it mentions that they tested all these RPMs with 6-cell packs.

I wonder if they mean 7.2 volts or a fresh charged 6 cell pack, which is over 9 volts. That peak voltage wouldn't last long (especially with 1200 mah) but should hold out for a dyno run.

[TheDiamondOne]

Very good question

[coxbros1]

EDIT: I just re-read the whole brochure and it mentions that they tested all these RPMs with 6-cell packs.

I wonder if they mean 7.2 volts or a fresh charged 6 cell pack, which is over 9 volts. That peak voltage wouldn't last long (especially with 1200 mah) but should hold out for a dyno run.

good point!

[juicedcoupe]

I've read that reflective paint will work instead of the tape. So I'm going to give this Tamiya X-11 chrome silver a try. I'll use the tape if necessary but would rather not.

[coxbros1]

You tryin to one up us? .....we'll u did! Nice!

[juicedcoupe]

You tryin to one up us? .....we'll u did! Nice!

Sometimes, my OCD flares up.

Thanks.

[Dadio]

Looked up a you tube review and one guy tried different reflective materials and even blue paint worked ! Seems they also run up to 99,999 rpm reliably !

[Coelacanth]

Now it's my turn to share how I'm building my motor dyno. A little late to the party, but I got to borrow from some of your guys' great ideas.

The trickiest part is finding a way to attach something to the motor shaft. I originally was thinking to use a spare motor pinion gear and somehow affix it to the shaft, and possibly a spare larger gear, but the idea of using a servo horn instead kept getting in the way of those intentions. Sticking a gear inside a spur gear would involve some kind of chopping and gluing. I opened up a beat-up old Futaba servo and found this white gear inside, it already has the splines for a large servo horn. I drilled a 3mm hole through the center and it snugly fit on the motor shaft.

The horn fits super-snug onto the splines, there's no way it'll ever slip. I actually need to put it in a vise to carefully pull it off once it's pressed all the way on. That's fine though because once it's on, it doesn't need to be removed.

Looking at the gear, I saw that the shoulder was thick and beefy enough for me to drill and tap a 3mm hole to install a grub screw. I cut down the rest of the outer part of the gear as it's not needed. I originally fabricated a motor mount from steel, but I found that the motor magnets, especially with the stronger motors, were significantly affected by the steel in the mount. I have a good feeling that would negatively affect motor RPM. So, if you're making your own dyno, use aluminum or plastic or some other non-magnetic material. I decided to use 2.5mm Kydex. I gave it the 90-degree bend by putting it in a vise and heating the area to be bent with a heat gun.

Next to do was the base plate. I didn't want to use up more of my Kydex sheet, and I thought wood would be too bulky. I have tons of this fancy acrylic sheet from my years doing computer case modding, so out came the Dremel and I chopped off a section of red UV-reactive acrylic. I don't intend to make it glow but it looks cool and it's lightweight and easy to work with, and I might as well use something that costs me nothing. I gave myself room to add the other dyno components, that's the next part of the project.

Here's the dyno station complete, I took a short video showing how it works...I just wanted to make sure it was functional and used a 360 Gold motor and a half-discharged 8.4V NiMH battery that was sitting in storage. All my LiPos are currently in storage mode so I'll need to charge one up and do some proper testing.

[Coelacanth]

Vid link to the functionality test:

[R6cowboy]

I originally fabricated a motor mount from steel, but I found that the motor magnets, especially with the stronger motors, were significantly affected by the steel in the mount. I have a good feeling that would negatively affect motor RPM. So, if you're making your own dyno, use aluminum or plastic or some other non-magnetic material. I decided to use 2.5mm Kydex. I gave it the 90-degree bend by putting it in a vise and heating the area to be bent with a heat gun.

I originally did the same, fab'd a motor mount out of 14 gauge steel today. I have some aluminum of the same thickness so I'll fab an identical bracket out of it. Now, for sh*ts and giggles, I'll test using both and see how much the steel bracket affects performance.

I borrowed juicedcoupe's pinion/spur combo idea. Drilled the center of the spur so the pinion fit tightly into it. Then tightened it onto an 1/8" drill bit and spun the drill full speed to make sure the spur was sitting true on the pinion. Then filled the small voids of the pinion teeth with epoxy.

[Coelacanth]

I originally did the same, fab'd a motor mount out of 14 gauge steel today. I have some aluminum of the same thickness so I'll fab an identical bracket out of it. Now, for sh*ts and giggles, I'll test using both and see how much the steel bracket affects performance.

Resized_20210221_202034_5145.jpeg

I think your steel mount might work better than mine did, as the motor would be mounted a fair distance above the horizontal foot of the mount. My initial design had the motor positioned only 1/4" or so from the horizontal foot of the mount. I could definitely feel the motor pulling into the foot while I tried screwing on the motor. I don't think the magnetic attraction of the vertical motor mounting part would affect performance much. Nice job epoxying on the spur gear, I considered that option too.

I kept some space open on my red base to mount an additional brushless ESC, so I can easily test both brushed or brushless motors.