What is overdrive?

[Juggular 4964]

I have a feeling that RC crawlers' overdrive means something different from overdrive in 1:1.  

I found this diagram for Element (Team Associated) Enduro. My CC-01 doesn't allow different ratio, so I've got no experience in overdrive (thanks, Tamiya).  

You can have the front turn at a slightly faster rate.  What's the benefit of that?  Is it for turning radius (since many crawlers lack the differentials)? That seems like a minor benefit. Is it good for crawling?  Anybody has experience in this?

 

[taffer 948]

My vanquish phoenix and Gatekeeper have overdrive...(yet to build them)

One of the advantages is when tackling a steep incline with the front wheels turning faster than the rear it apparently enables a smooth ascent, if the rear wheels turn at the same speed as the front then there could be a tendency for the truck to flip backwards more easily.

Look for YT vids on the vanquish phoenix, a lot of people show demos of the features Inc overdrive 

[toyolien 4681]

Overdrive put simply is: allowing either the front or rear wheels (or axles in terms of crawlers) to spin faster than the other.

With crawlers it is almost essential. Most 'trail trucks use something like 5% to 12% overdrive to the front wheels. Competition crawlers use anything up to 40%. However, there is a downside. Drivetrain wear. Trail trucks that are driven more that comp trucks use a small amount of overdrive to minimise wear. Comp trucks that are usually placed at the comp start and just driven for that particular course can have much great percentage of overdrive.

With regards to Tamiya car, in particular the new XV02, Tamiya have spec'd the car with the ability to run a small amount of overdrive to the front or rear wheels depending on how you want the car to behave. But, they do say that you should also use a slipper clutch or centre diff if you opt for overdrive. This is to allow some 'separation' between the front and rear wheels to prevent drivetrain wear.

Hope my rambling makes some sense?

[Big Jon 684]

Overdrive on crawlers helps turn radius, and helps reduce looping out on long or steep climbs. Trail rigs use less; comp rigs use more. I use 6% on my Enduro, as I found 12% to reduce run time more than I was willing to accept, and performance is more than adequate. On a trail rig especially, it’s a matter of personal preference - everyone uses them slightly differently.

One tip about Enduros: the inner pinion bearing is inadequate. It’s only a 5X10, and fails quickly. The bearing bores are not aligned correctly, either (my hard axle housings were  off 0.023”), which probably doesn’t help. You can use a brass bushing in place of the bearing, or drop the housings off at the machine shop and have them cut for a 5X11 bearing. Most crawler axles are using a 5X13 bearing, which is bulletproof, but there’s only enough beef for a 5X11. That’s the only real flaw the Element Enduro has; I’ve enjoyed mine a great deal.

[Alexei 547]

overdrive is also used with 4 wheel drive drift cars, although that was the thing before rear wheel drive drift chassis' appeared.  having overdrive on the rear wheels will give more over steering, making them drive more like a RWD car while being a 4WD chassis.

[moffman 5752]

The only overdrive I know about is the type you got in 1/1 cars? Way back in the 70's my dad had a triumph dolomite sprint which had a 4 speed gearbox and a overdrive button on the top of the gearstick (very much like James bond Aston Martin db5 with the ejector seat button) it was just so cool and in British racing green basically it was a fifth gear that you didn't have to use the clutch! Incidentally the triumph dolomite was the first car to use a 16 valve engine which decades later became the normal thing in manufacturing of engines (just a bit of useless trivia)