Mid Motor Scorpion

[DennisM]

I´m in the middle of making a new gear set, mainly from Tamiya gears.
Have no clue how it´s going to end up

[Coelacanth]

I´m in the middle of making a new gear set, mainly from Tamiya gears.
Have no clue how it´s going to end up

A blob of shredded plastic?

Seriously though, I'm interested to see a mid-motor Scorpion. Neat project.

[SFC K]

This is a cool project. Curious too see how it turns out.

[Phin]

Two words: Belt Drive.

Since it's only two gears in the trans case you won't have to flip anything around to get the wheels spinning in the right direction. Just need a couple of relatively inexpensive 3racing pulleys for the pinion and main shaft and the right length belt.

[Coelacanth]

Two words: Belt Drive.

Since it's only two gears in the trans case you won't have to flip anything around to get the wheels spinning in the right direction. Just need a couple of relatively inexpensive 3racing pulleys for the pinion and main shaft and the right length belt.

Excellent idea! Add to that some slots drilled in the motor plate to allow adjustable motor mounting, then you don't have to find the perfect-length belt.

EDIT: I was actually looking at parts like this a few months ago, but never had an application for it. You just need to find a way to mount the pulley on the diff shaft; probably a cross-pin would be possible?

http://www.ebay.ca/itm/CY-17-PU-3Racing-Aluminum-Belt-Pulley-for-HB-Cyclone-/360648721444

http://www.ebay.ca/itm/RC-Drift-Car-CS-Aluminum-22T-Center-Pulley-3Racing-Sakura-D3-Tamiya-MST-/330934910957

http://www.ebay.ca/itm/3-Racing-Aluminum-Pulley-19T-For-V-One-R-/151022599978

[Phin]

I've been considering pulleys to replace the gears outside the Scorpion for some time now to make changing gear ratios much easier. The 3racing pulleys come in lots of tooth counts and fit a 4mm shaft same as the top shaft in the Scorpion trans. They attach with set screws (I believe from two sides) which should be sufficient and there's no need for set pins.

http://os.3racing.hk/products_list.php?stype=ctp&catalog_key=107

They're the standard 3mm HTD belt pitch that most touring cars use so finding the correct length belt might not be difficult. A bearing mounted on a shaft somewhere in the middle of the motorplate can be used to add tension.

[DennisM]

That belt drive could be the solution
I´ll see if I can find some short belts.

[ron]

This is cool, got me excited. I am thinking along the same lines too. The prob with the gears of the scorpion/tomahawk/ beetle are they are too coarse. Great for high torque motors, they will transfer the toughest of torque without breaking, but are noisy.

A belt system on the outside is the way to go, man that setup will be smooth as. But a trany change inside the gearbox would make the buggy perfect. I got many nylon fine tooth gears, will try. Belt driven and finer pitched gearing will see it purring like a kitten, when she runs and thats all that matters! acro customs has a mid mounted motor, he did it to his assult or advance.

A mid engine mount is neater and more compact.

[DennisM]

Thanks
You should have a look at Hcp22`s awesome build "Blueprint Scorpion" found in the Kyosho section.
He used an Assult gearbox, swapped, If memory serves me correct.

I´ve been looking for a ball diff (not keen on paying a days salary for a Thorp) But haven´t found anything so far.

Here´s a couple of update pictures.

[Phin]

Looks good. What pulleys did you go with?

[DennisM]

Thanks Phin,

The pulley on the input shaft is from a V-one RRR fitted to an alloy rim crosspin adaptor.
The tensioner is from a Corally C4 and the pinion on the motor is std. 0.8 module.
The belt is from the plastic Lazer (Alpha)

[Hcp22]

Nis project Dennis

[ron]

I had not seen Lars Blueprint scorpion, he's a legend. Yea, this is what Acro customs did. That is really clever way of using the engine's gearbox setup to install a mid mounted motor

What is the pulley ratio on your setup? You know with the stock setup, the trany had 3 gear reduction in sequence, 2 outside the gearbox and one inside to achieve that speed at the wheels. With the pulley setup, won't the motor be putting out a lot of rpm on the wheels and getting pretty hot doing so? I am not trying to be a smart ass here, just asking if you don't mind.

Love the pulley with the belt, you have made a scale-looking scorpion more real with the belt drive, man that is just real. I am so doing that too. I think you can employ chain drive too, for that wicked look, but won't be as smooth as belt drive.

I got into the thorp diff fever too, damn expensive, kept my money in my pockets thank God Thorp is a ball diff, although compact, I would not know of its performance compared to the norm geared diff setup. I know if you keep it a bit too tight, it does not act a diff should during turning, the wheel making the wider arch will not be allowed to turn as fast and you won;t have a tight turning circle. During a straight acceleration, the diff will mostly slip if its lightly tensioned and act somewhat like a slipper clutch, thats a good thing if you don't have a clutch but you are wearing out your expensive ball diff. you can easily employ a slipper on the spur. I will stay with the good old fashioned geared diff. There is a reason why ball diffs is not employed in real cars even though the design and cost would be lower than a geared diff.

[Phin]

...
What is the pulley ratio on your setup? You know with the stock setup, the trany had 3 gear reduction in sequence, 2 outside the gearbox and one inside to achieve that speed at the wheels. With the pulley setup, won't the motor be putting out a lot of rpm on the wheels and getting pretty hot doing so? I am not trying to be a smart ass here, just asking if you don't mind.

Love the pulley with the belt, you have made a scale-looking scorpion more real with the belt drive, man that is just real. I am so doing that too. I think you can employ chain drive too, for that wicked look, but won't be as smooth as belt drive.

....

It helps that the internal transmission ratio on the Scorpion is 2.8:1. I believe the V-One pulley Dennis is using is 32T, and a pulley for the motor can be found as low as 10t or 11t, so the belt setup should handle gearing for a stock brushed motor.

The real potential of the belt drive though is to reach the gear ratios you need for the torque of a 17.5t brushless.

[DennisM]

What he said