Furadi

I've known about this feature on my Mamba X but just now getting around to using it.
- 94 amps peak
- 31.8k rpm
- 175F motor temp (after 10 minutes)

This is on 3s 2650kv. Curious to see how it compares to a typical 4s / 1900kv buggy.

robert@castle

Everything looks pretty good to me. Ripple is under control. Battery and BEC voltage is stable. It looks like the first datapoint it captured might be bad because of how low the BEC and battery voltages show in their min value, but I don't see anything that looks like it was an issue during the run.

Just in case you didn't know, you can zoom in by dragging a rectangle over the graph to see a smaller section of the data. You can also turn off data sets by clicking their label down at the bottom.

Furadi

Thanks for the reply! How do the temps look? This was in 80 degree weather...

robert@castle

They look absolutely fine to me. You shouldn't have any issues with that setup.
I find it interesting that the ESC temp starts 10 degrees high and the motor temp starts 10 degrees low. If it was a fresh run, both should start at ambient. The thermal sensors used in hobby products arn't great and are hard to get precise numbers out of.

Bry195

frewster

iTrader: (1)

No. Something is extremely wrong if you're getting efficiency that low at higher loads. There isn't nearly enough cooling to keep up with those kinds of losses except at low loads.

Furadi

Hmm?

frewster

iTrader: (1)

Sorry for the confusion, I was talking to Bry.

robert@castle

System should be closer to 85-90% efficient. 850-900 watts output power.

Bry195

Bry195

robert@castle

There is a reason we don't make a 2 pole ROAR motor. The two pole design specified by ROAR is actually a rather poor design. All of our motors are 1, 1.5, or 2 turn motors and have 85-95% efficiency. We prefer adjust the kv of the motor by adjusting the length of the stator or the magnets. In 1/10th scale motors, we make between a 1900kv and a 7700kv motor with those 1, 1.5, or 2 turns configurations. Specifying a motor by turn count is almost meaningless because there are so many other factors that contribute to the actual RPM of the motor, but the 2 pole design has most of those locked down to keep motors as consistent between brands. When we developed our sensored motors we tested our 1406 4600kv motor vs a 7.5 turn motor on our dyno and put a 300 watt load on both. The 7.5 turn motor hit 300F in about 2 minutes and it stopped working. Our 1406 4600kv ran for 5 minutes and only got to about 230F.

In 1/8th scale there was no electric buggies until we came out with the original Mamba Monster and 1515 motor because there was no motors that could survive the load of 1/8th scale. We had to start the e-buggy class by making electric conversion kits for nitro buggies because no one made electric buggies at the time. In 1/8th scale, most of the other motor brands are similarly efficient because they have to be.

Also worth mentioning that the motor he has can do over 2hp and our 1/5th scale motor, the 2028, can peak over 10hp from a motor about the size of a soda can.

Furadi

It's interesting. Part of me wants to try either 1800 or 2200kv on 4s but at this point there's no reason too. I get 12 minutes of run time at Amain race pace on my 3s 5400mah packs with this setup. My only remaining question will be heat once we get into the 90's.

robert@castle

1800kv would probably run longer on 4s(of the same size) because the current would be lower. I'd say peak would be 70-80 amps. The watts would be about the same, but since the voltage is higher the amps would be lower. The weight of the extra cell would probably cause the wattage to be slightly higher, but the overall current would be lower. Current causes heat, not wattage, so it would probably run a bit cooler. Max RPM would be lower with a 1800kv of 1900kv, and slightly higher with a 2200kv. The 2200kv would have quite a bit more torque and might actually make you slower because it would be harder to control. The 1515 is a bit overkill for a 1/8th buggy unless you are speed running and want to run a tall gearing and 6s. If you are able to run competitively, I'd probably leave it be.

If it is 20 degrees hotter outside, the esc and motor will be 20 degrees hotter at the end of a run. Ambient vs ESC temperature pretty much scales linearly. You shouldn't have any issues at any temperature below 130F. You'll give in before it does.

Furadi

Awesome! That's super comforting!