Brushless Top Speed issue, RPN Revving up and down

[D3FCON]

Extremely hard to explain with out showing you so i made a chart to help describe the issue I am having. The car reaches high speed then bounces up and down in rpms until I release the throttle or apply brake. It is really annoying. Any ideas hobbyists ?

I'd like to be able to maintain the high speed without the RPM dramas. it has no issue getting to max then the issue arises.

HOBBY WING 4000KV 3652 w 50a ESC on 5000MAH 3S Lipo (45c) Issue

 

[Notorious J]

Extremely hard to explain with out showing you so i made a chart to help describe the issue I am having. The car reaches high speed then bounces up and down in rpms until I release the throttle or apply brake. It is really annoying. Any ideas hobbyists ?

I'd like to be able to maintain the high speed without the RPM dramas. it has no issue getting to max then the issue arises.

HOBBY WING 4000KV 3652 w 50a ESC on 5000MAH 3S Lipo (45c) Issue

That's amperage ripple. You need to modify one, or all, of three things. 1- A better esc. 2- A higher C rated battery 3- Add a capacitor pack. I'm not a pro at this, but I started speed runs last summer and was getting a lot of advice from those who knew much more than me. The ripple happens when the motor asks for more current/amps than can be provided. One of the issues is heat which will affect the esc's performance. The easiest test would be just a better battery with a higher C rating. An esc that handles higher amperage gets expensive, but it all depends on what you're end game is. A capacitor pack is more complex for installation, but it will help store some energy so your esc doesn't have to work as hard. One other thing I learned is to be much more even on throttle pull. The longer and slower you bring the car to top speed, the less ripple you will experience. At some point you will still hit the limits of the electronics, but you might be able to achieve a slightly higher top speed without changing anything. Hopefully others here with more experience than me will also chime in and correct me if I've made any mistakes. Raz Shifrin, Liberty Francis and Philip Jolley are very good at explaining the needs of achieving higher speeds, so if you have the time, check out these YouTube channels for in depth info.

 

[tntpoof]

coming up with a home made graph is helpful but its still a unknown of whats going on...NJ could be correct in his reply.. Id also look into a higher amp esc with a more powerful battery as in C rate..I push many of my electronics to and past there stated limits in my speed runs..but my speed runs are limited to few seconds.. I use a vast varietty os esc/motor setup along with mostly smc batteries...posiden motors .kontronics esc.
KOSMIK (kontronik.com)
Brushless Motor - Poseidon RC
Welcome to SMC Racing (smc-racing.com)

 

[BobP]

can't you set the throttle limit on your transmitter to the point that you get the best speed? that way your not calling for more than your esc can put out.

 

[D3FCON]

Yeah I could do that. Had not thought of it. Will look for a 69c battery and a new esc too