[CMOTD]

Does anybody know the technical reason for inline motored cars jumping sideways under full braking please? Sidewinders and anglewinders rarely do it. Upmarket cars like Slot.It are as equally prone to this as Scalextric ones. I know it is easy enough to cure by backing the brakes off a bit but why do they do it?

[KensRedZed]

The physics of inline drive is mechanically poor. The gears meet while on an angle, straighten out, then twist away from each other.

Sidewinders have a slightly smoother mechanical mesh. That translates into less friction on an equal motor with the same ratio.

Inline drive has more brakes because of the added mechanical resistance. That's why they tend to lock up moreso than sidewinders.

Chris Walker would be the expert here. I'm just taking a wild guess based on how my cars run.

[Nonfractal]

The armature has momentum.
(Angular momentum)
When you take an inline motor from full throttle to zero, that momentum is transferred to the chassis, putting torque on the chassis which lift one rear wheel pushes the other down to the track. 

You can see the effect clearly if the motor is revved and braked sharply outside the car.

The same can be seen on a BMW boxer engined motor bike. 
The crankshaft is inline and transfers the momentum to the frame when the throttle is blipped. 

I have to say though, that the effect in a slot car is rarely enough to upset the handling in any severe kind of way.
I run king30 motors inline in AllSlotCar F1 cars and have never suffered with "jumping sideways" as you describe. 

Alan

[Scuderia_Turini]

Hello Brian,

Adding to Alan's technical explanation, the motor gets driven as a generator by the rear axle and the can/body of the motor re-acts and tries to twist the chassis around with it.
The opposite twist occurs when the motor drives the axle, resulting in the car stepping out of line under harsh acceleration.
(Unless you have an electronic controller to dull the harshness)

Leo

[rallyhub]

At an inliner configuration the crown wheel is placed off-center (radius of the pinion) on the rear axle.
In this way, the moments left and right are not in balance.
An inliner configuration results also in less weight and grip on the rear axle compared to a side- or aglewinder.

Positioning the inliner motor off-center in the floorpan, would result in a car that reacts different on left hand- and right hand bends. 
(I guess that is the reason why the inliner motor is always in the center of the floorpan, with a disadvantage during braking).

rallyhub

[autoavia]

My understanding is that an inline car will always move sideways slightly under braking because the crown gear is off centre in the chassis but the movement is magnified when the brakes are turned up so far that the rear wheels lock. Turning the brakes down a little stops the rear wheel lock and reduces the sideways movement.
 The problem can also be magnified by poor car set up such as a rear axle which isn't parallel to the track.

 Incidentally full size go karts have exactly the same problem. The offset drive to the motor doesn't seem to have too much effect but the offset disc brake on the rear axle produces a very noticeable turning moment when you brake hard which affects the steering.

[dvd3500]

Yep and you can use it to your advantage going into a curve depending on how it behaves..
I had a go kart that had a very pronounce tendency to pull to the left. It was so bad people following me thought I would spin if I hit the brakes hard and early so they backed off.