Hey,
I have recently finished my custom 6x6 Losi XXL.
It is powered by 3 separate 600kv outrunner motors driving directly into the diffs, each with an ESC.
Mechanically the build was a success but I'm having an electrical issue.
When I accelerate from a stand still, the motors will shudder. If I blip the throttle a few times it will usually begin to roll (not always) and if I crack the throttle with any haste it will just sit there and squeal.
I have decreased the timing to the minimum and increased the acceleration/punch to max which has decreased the severity of the problem but it is still not good enough.
It will spin up with no load on the tyres.
I've been told to add more capacitors in parallel with the batteries but wanted to get some more opinions on how to go about this.
Cheers
Ben

with the tires not connected, the motors just spinning freely, do you still have that problem?

Yep the motors spin free with no load, it only requires a small shove to get it into a range that the motors can accelerate. Most times it will take off from a stand still but it is shuddering and whining all the way.

Try going teh oteh rway - low starting power and see if its any better. Cogging can be caused when batts can't supply the current demanded by the motor.

What kind of batts are you running, mah and C rating?

I would also like to know what types of controllers you are using. My guess is this is a pretty high voltage setup, and not many controllers out there that handle high voltage will have good starts.

I have experimented with low timing low punch, low and high respectively, high and high, high and low. The best result is from low timing high punch.
I run Turnigy 2s 5000mah 40-50c
I've ran it on 4s 2p (4x batteries which should be more than enough grunt, I think it works out to be 400amp constant) & 6s 1p.(3x batteries)
I've turned off two ESC's and still have the same result from the 3rd.
My ESC's are Hobbyking 150 amp.

It seems from stories, my experience and a mates that high amp ESC's seem to cog.
I've previously had an Ezrun 35 or 60 amp (can't remember) speedy with a 5.5t setup on a 2s Lipo, geared very high and never had an issue.

I suspect the issue is the very low kv motors. Assuming this is a non sensored setup, non sensored escs tend to cog with low kv motors much more than high kv ones. Something like a 5.5T (~7400kv?) will usually work pretty good, but a 17.5T (~2200kv) frequently won’t work nearly as smoothly for example.

The direct drive may be contributing, although those are low rpm motors it’s still quite possible that it’s too much gearing depending on the size and torque capability of the motors. What motors do you have?

The motors are 600kv 55-50 Turnigy sensorless outrunners. They were my choice as I thought the outrunners would produce the torque to get it off the line in a direct drive setup.
I'm not totally sure but the gearing seems to be right as once it is moving (slower than walking speed) it has plenty of grunt.

Do you think that higher kv motors running through a reduction would be the answer?

Cheers all