Lay down servo mounting

[MonkeyChimp]

Would anybody with relevant experience please explain the pros/cons of lay down servo mountings? My understanding is that by virtue of the servos positioning, you gain an increase in torque, and possibly steering angles as well. However, if it were that peachy, most, if not all servos would be positioned as such. There has to be a downside.

For context, I plan on experimenting with a lay down mount in a TRX4 with a 324mm wheelbase, and a HH SHV 500V3. I’m running a Mamba X with a Puller Pro 3500kv, 45T spur and 9T pinion. My son and I use our TRX4’s primarily for trail bashing.

I thank you in advance for your responses.

MC

 

[Ninomaniac]

Lower CG. That is all.

 

[Goro Majima]

Pros: Lower center of gravity like ^ mentioned, more torque like you said, more room between servo and hood if you want to add scale engine bay or extra area for wiring/modules if you have interior.

Cons (minor): Servo using up floor space so if you plan to have a servo winch you'll reposition it elsewhere.

 

[Ninomaniac]

How does it have more torque laying down? Looks like I'm missing something.

 

[Goro Majima]

How does it have more torque laying down? Looks like I'm missing something.

The arm is able to sit lower than it can in the upright position. It's the closest you can get before moving to servo on axle.

 

[Benp]

This is on my to do list for better articulation with my setup.

I have the lay down mount from IERC Scaler.

https://iercscaler.com/shop/ols/products/trx-servo-lay-down-mount

 

[svt923]

The arm is able to sit lower than it can in the upright position. It's the closest you can get before moving to servo on axle.

Once the servo starts swinging in an arc upwards, the servo is now using a portion of it’s power to move in a direction that does not translate to steering movement. The further it gets in the travel, the servo is essentially swinging upward in order to generate left and right movement at the wheels which is quite an inefficient use of power. With a CMS setup, having the servo swing in the same plane as the knuckles is the most efficient use of the servo’s torque.

 

[MonkeyChimp]

With a CMS setup, having the servo swing in the same plane as the knuckles is the most efficient use of the servo’s torque.

Thank you. That makes sense to me. I knew there had to be a reason as to why lay down set ups aren’t ubiquitous. But isn’t a lay down mount still considered a CMS? Or were you only responding to the member who mentioned axle mounted servos?

MC

 

[Goro Majima]

Thank you. That makes sense to me. I knew there had to be a reason as to why lay down set ups aren’t ubiquitous. But isn’t a lay down mount still considered a CMS? Or were you only responding to the member who mentioned axle mounted servos?



MC

Lay down mount counts as CMS, yes. Another benefit.

 

[svt923]

Thank you. That makes sense to me. I knew there had to be a reason as to why lay down set ups aren’t ubiquitous. But isn’t a lay down mount still considered a CMS? Or were you only responding to the member who mentioned axle mounted servos?

The same concept applies to both CMS and axle mounted servos. The best axle mount setups, like you would find on any high performance comp crawler, will have the servo arm rotating the same way as the knuckles. The performance difference between an average servo on axle setup and a good CMS can be debated. The biggest difference is that it is quite easy to screw up the geometry on a CMS and turn it into a crap setup while the basic “drop a servo on top of the axle housing” type AMS is hard to mess up.

 

[Craigeo]

This is on my to do list for better articulation with my setup.

I have the lay down mount from IERC Scaler.

https://iercscaler.com/shop/ols/products/trx-servo-lay-down-mount

Just ordered that a lot more for my TRX4. Should be a fun build.

I appreciate the link and information!!

 

[HumboldtEF]

Well since theres some some technical talk I'll just add that I always assumed that a lay down servo (CMS) would add a bit of bump steer due to the arc of the horn changing the angle the drag link.

Now I know thats probably not a huge concern for folks that do this mod as they're probably not ripping around like a scaler might.