Wraith steering issue

[crawler2.2]

I am running a MMP and Tekin 13.5 with a mild torque savox servo on 3s. I am using a glitch budget. My steering wants to pull hard to one side once I get into higher rpm. The steering is centered so it's not the trim. Anyone else seen or experienced this?

[evan03]

Which savox? It might not have enough power to hold under a load

[Tio Loco]

This came up yesterday in the 4WS thread. I'm not an expert by any means, but here's my take... I'd love to hear an engineer explain it better or totally debunk my theory.

When a front wheel turns to one side or the other, whether by steering, steering slop, hitting an obstacle or whatever, the normal straight line rolling motion is turned into a diagonal 'drag' resistance. This makes the wheels try to turn even further. The the faster you go, the more turning force is applied against the servo.

You say you have a 'mild' servo, so I suspect it just can't stand the pressure that the tires are applying. You brought a knife to a gunfight.

[crawler2.2]

Savox SC0251MG Digital Servo

esc bec is set to 6v also the lipo c rating don't help. I used 25c and 40c

[crawler2.2]

This also happens on smooth pavement

[JeremyH]

What ESC? External BEC?

[Tio Loco]

Batteries (2S or greater) don't matter, nor does C rating.

Like I wrote, steering slop, unbalanced tires or whatever can initiate the pull to the side which then starts tugging on the servo.... everything that I've read says a 300 oz. servo minimum.

[crawler2.2]

I ran a 400 oz before same result. ESC is mamba Max pro. No external bec but I use a glitch buster on receiver and 6v internal bec

[JeremyH]

Originally Posted by crawler2.2

ESC is mamba Max pro. No external bec

That is your problem. 3S lipos and an internal BEC are not supplying enough juice to your servo when the motor is drawing a lot of amps.

Get an external BEC.

[crawler2.2]

So the internal 6v bec and the capacitor on the receiver isn't enough?

[Calderwood]

Originally Posted by Tio Loco

This came up yesterday in the 4WS thread. I'm not an expert by any means, but here's my take... I'd love to hear an engineer explain it better or totally debunk my theory.

When a front wheel turns to one side or the other, whether by steering, steering slop, hitting an obstacle or whatever, the normal straight line rolling motion is turned into a diagonal 'drag' resistance. This makes the wheels try to turn even further. The the faster you go, the more turning force is applied against the servo.

You say you have a 'mild' servo, so I suspect it just can't stand the pressure that the tires are applying. You brought a knife to a gunfight.

You asked for a engineer to explain it but you may be waiting for a while before one shows up so I'll give it a stab like O.J. Caster makes the wheels want to return to straight when ever the vehicle is moving forward. Think about the front wheels on a shopping cart. If the pivot was right above the wheel it wouldn't track well. You have to have the pivot in front of the wheel to make it track. This is like positive caster. More positive caster is like moving the pivot point on the shopping cart wheel further forward. It will track even better but will be increasingly hard to steer away from straight.

Originally Posted by Tio Loco

Batteries (2S or greater) don't matter, nor does C rating.

Like I wrote, steering slop, unbalanced tires or whatever can initiate the pull to the side which then starts tugging on the servo.... everything that I've read says a 300 oz. servo minimum.

Batteries definitely DO come into play with an issue like this. The bec has to do a lot more work reducing the voltage from a 3 cell than it does reducing the voltage from a 2 cell. This results in the bec not being able to provide as much current operating on 3 cell as it would be able on 2 cell.

[frdtrkguy]

Originally Posted by crawler2.2

So the internal 6v bec and the capacitor on the receiver isn't enough?

I'm with Jeremy, install a bec..

[Dostradamas]

I agree the internal BEC is not putting out enough power but do you guys think 222oz is enough torque for that setup?
My 400oz is almost enough & I only run at 35T speed.
You need more servo torque as well as a BEC (or a 2s LiFe for servo only.)

[Tio Loco]

Thanks Nigels_world.... nice examples.

As to the batteries, also good to know. I suppose I was thinking more from the C rating aspect, but didn't know that 3S putting more load on the BEC.

[crawler2.2]

Well after reading I tested on a 2s. That's seems to be the answer. I'm going to run 2s for a while. If the power isn't enough I'll install a castle bec. Thanks a lot everyone.

[Meatwad]

Originally Posted by Tio Loco

Thanks Nigels_world.... nice examples.

As to the batteries, also good to know. I suppose I was thinking more from the C rating aspect, but didn't know that 3S putting more load on the BEC.

Any bec's job is to kick down the voltage, in that process heat is created. Enough heat kills everything.

Originally Posted by crawler2.2

Well after reading I tested on a 2s. That's seems to be the answer. I'm going to run 2s for a while. If the power isn't enough I'll install a castle bec. Thanks a lot everyone.

2s has worked for me, as going from ~8v to 6v is alot easier than going from ~12v to 6v. Although not the best option for electronics health, an external bec is your best option. Crawling/trailing will always put more stress on steering servos than go fast applications. Wheels are always easier to turn when moving, with a servo saver and not bound up against obstacles.

[JeremyH]

Originally Posted by crawler2.2

So the internal 6v bec and the capacitor on the receiver isn't enough?

No.

[rcmedic]

Even a hobbyking $6-$10 bec would be better than internal bec. Your esc temp now will go down about 5-10 degrees with an external bec

[crawler2.2]

Originally Posted by rcmedic

Even a hobbyking $6-$10 bec would be better than internal bec. Your esc temp now will go down about 5-10 degrees with an external bec

Really?

So would the same be said for my backslash? slash 4x4 with 1/8 buggy tires, MMP esc, Savox 2220z servo, and 1415 550 2400kv 4 pole. I feel its geared kinda low, but heat still rises. I'm using the internal bec here as well.....

[rcmedic]

Originally Posted by crawler2.2

Really?

So would the same be said for my backslash? slash 4x4 with 1/8 buggy tires, MMP esc, Savox 2220z servo, and 1415 550 2400kv 4 pole. I feel its geared kinda low, but heat still rises. I'm using the internal bec here as well.....

Yes, my ae2 always thermaled before external bec