Diffences between Moa and Shaft driven

[billys]

Can someone please explain to me what is the difference in perfomance between Moa and Shaft driven R/C crawlers. I am not refering to actual visual differences like the fact that the motor is over the axle but I am refering to differences in performance.

 

[Johnnysplits]

Better traction from having the added motor weight on the axle. That's about all I could see. Personally don't like them.

 

[filotr14lsdude]

With moa you have a electic controlled dig. Because you can drive each axle independent. You have better control of the wheels and can drive more interesting lines

With shafties you have a mechanical dig, this allows only the front or rear axle to lock, depends on how you have the dig unit set up.

 

[2WheelFlyer]

With MOA you have a lower CG because the motors are down low so you can climb and descend steeper lines and you usually have good fore-aft stability too because you have 2 smaller motors right on the axles, instead of a big one sitting up high (creating a teeter-tooter like fore/aft weight transfer depending on the angle or the rig) in the center of the vehicle. As Johnnysplits said, that helps traction because you have the weight closer to the contact patch of the tires.

In some MOAs you could have a bit of a wider turn radius because the motor cans don't allow your steering linkage to turn in so much, but you can use wheel spacers or bend the links outward a bit if you need a smaller turning radius. That's why some MOA designs go to 4 wheel steer to help the turning, not comp legal, and I usually don't like that eiher.

Shafties usually have the motor in the middle, so that causes a bit of problem of locating the batteries also high up (depending on what kind you use), because the space is already occupied by the motor. MOAs have space in the center of the chassis because the motors are not there and the battery can ride low. Shafties can suffer from the torque effect of the motor on the chassis if not properly set up. Shafties do not suffer from clod stall because the same motor drives both axles, although you could have problems with the slipper clutch if it's on a tight bind. Shafties have the motor better protected from water and rocks than MOAs because it sits up higher.

MOAs have generally better clearance between the wheelbase, because you don't have angled front and rear driveshafts, so you get less hung on obstacles and can almost always have good articulation not affected by driveshaft angles (and don't get driveshaft wear and tear).

I don't know if anyone has actually measured power loss through a shaft driveline (like 1:1 vehicles, were engine HP is not the same as WHP) compared to the more direct drive of a MOA.

 

[billys]

THANK YOU VERY MUCH! That is the answer I was looking for. I could appreciate if you could clarify me one more thing. I believe that shafties although have worse traction than MOA I think have more articulation as suspension travel is not restricted by the motors. Is that correct?

 

[filotr14lsdude]

Moa and shafties both still have the potential to have 90degrees articulation. You limit with shocks.

So the motors don't really get in the way that much.

 

[v84x4]

With MOA you have a lower CG because the motors are down low so you can climb and descend steeper lines and you usually have good fore-aft stability too because you have 2 smaller motors right on the axles, instead of a big one sitting up high (creating a teeter-tooter like fore/aft weight transfer depending on the angle or the rig) in the center of the vehicle. As Johnnysplits said, that helps traction because you have the weight closer to the contact patch of the tires.


Shafty motors are the same size as MOA motors
"CAN" 550 Motor—A slightly longer version of the 540 motor and has nothing to do with the difference between Shafty's and MOA's

In some MOAs you could have a bit of a wider turn radius because the motor cans don't allow your steering linkage to turn in so much, but you can use wheel spacers or bend the links outward a bit if you need a smaller turning radius. That's why some MOA designs go to 4 wheel steer to help the turning, not comp legal, and I usually don't like that eiher.


On a MOA the motor sits behind the axle and will not interfere
with the steering in the front of the axle at all.
It's the Shafty axle Diff housing or MOA Gear box that gets in the way
of the steering rod and can be easily fixed on either type of rig

Shafties usually have the motor in the middle, so that causes a bit of problem of locating the batteries also high up (depending on what kind you use), because the space is already occupied by the motor. MOAs have space in the center of the chassis because the motors are not there and the battery can ride low. Shafties can suffer from the torque effect of the motor on the chassis if not properly set up. Shafties do not suffer from clod stall because the same motor drives both axles, although you could have problems with the slipper clutch if it's on a tight bind. Shafties have the motor better protected from water and rocks than MOAs because it sits up higher.

Although Custom built rigs can sometimes present a problem finding a place
to mount your battery
ALL Production Rigs come with a place to put the battery and therefore it's not a problem


MOAs have generally better clearance between the wheelbase, because you don't have angled front and rear driveshafts, so you get less hung on obstacles and can almost always have good articulation not affected by driveshaft angles (and don't get driveshaft wear and tear).


On a 4 linked Shafty, the Driveshafts are hidden and protected by the Lower Links and the lower links help glide you over the rocks ;-)
A 4 linked shafty can have just as much articulation as a MOA
However, On a Leaf Sprung Shafty you are correct

I don't know if anyone has actually measured power loss through a shaft driveline (like 1:1 vehicles, were engine HP is not the same as WHP) compared to the more direct drive of a MOA.

One of the many things you CAN NOT do with an MOA is run bigger Can Sized motors Like 1/8th scale brushless
Also you are stuck with the limited gear ratio since MOA's don't have a SPUR Gear

As far as performance.............
I have seen many Awesome drivers take a stock rig (Shafty or MOA)
and out drive the guy whom has Thousands of dollars invested in his rig

I think your asking the wrong question............

Heres what you should be asking yourself:

#1 is there a local HS near you that has COMP's Using MOA's ????

#2 what do you really want to do with your rig (Comp, Trail ride, Jump and bash) ?

#3 What is your Budget (MOA's can cost twice as much as a Shafty depending on your upgrades)

The biggest thing to remember is:
What will bring you the most happiness ;-)

Hope this helps

Best Regards Rick

 

[2WheelFlyer]

Rick, you can have a relatively good performing MOA rig with 2 390s, but on a shafty for example you don’t want less than a 540. On a shafty you can go big like the 1/8 brushless you mention or even 2 motors like an e-maxx, but AGAIN, you are moving all the weight and CG up, the opposite of what you want for crawling, and that is exactly what I meant by saying you can have 2 smaller motors on the axles rather than a big one in the center. On a MOA, you have the motors and their weight closer to the contact patches of the tires. In some MOAs that come with 380 or 390 motors you can fit a 540, but you start having clearance issues and a 550 is impossible to fit, others that are designed for 540s that is not an issue.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>
That brings me to the steering issue I mentioned in the MOAs, That’s because the bigger the motor, the can lenght makes you move the links outboard, and that’s the first thing your tires hit (not the steering linkage), specially if you modified it for more servo throw and angle. You can’t move them in because of the gearbox and motor, and you can’t move them out because they rub so you end up “S” shaping them sometimes. This can be an issue to with a ladder frame shafty but not on a narrow chassis shafty where you get away with ridiculous amounts of steering angle, no need for 4WS.<o></o>
When I mentioned the problem of locating a battery I didn’t say you can’t fit one, of course you need one to run the truck right? But MOAS can run them down low within the wheelbase, not high up. The battery can be one of the most dense and heavy components in a crawler (depending on type and size) so you want it as low as possible that’s why some people end up strapping theirs to the front axle. That is why Axial even let you play with the battery location by moving it to where you want it depending on what you want to do with the truck. But, in a shafty it will inevitably go high up, usually at the front so you don’t backflip when climbing (and still do easier than a MOA), but you can front flip when descending (compared to a MOA of the same weight at the same angle).<o></o>
Again, the idea is to keep the CG as low as possible and divided on the axles for fore/aft stability; it’s the opposite of what you want for example in a track car, where all the mass is centralized within the wheelbase and closer to the CG for quicker turning (by resulting in a low polar moment of inertia).<o></o>
When I mentioned the clearance within the wheelbase is better in a MOA, is because you can bend the links all you want without exposing a shaft. Some shafty designs might get away a bit better than others in this respect, but on a MOA this is not an issue.<o></o>
You did mention something important in the gearing though; if there are no different gearsets for a MOA you are limited to swapping a pinion that is a couple teeth smaller and that’s it. Shaftys are easier to tailor in the power/speed combo without changing the motor by just swapping the spur gear and pinion sizes or even using a 2 speed gearbox.<o></o>