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TOPIC: Grasshopper & Hornet - rear axle suspension

Grasshopper & Hornet - rear axle suspension 2 weeks 4 days ago #56109

I cannot get my mind off that Tamiya may have designed it like that just to tease the mechanic instinct in us all. But then they release the Hornet with an additional dimension of trickery. Perhaps it is a competition? Perhaps it is a lure to solve a larger problem for a ... secret government project? In any case that rear end of these grasshoppers and hornets have been grinding in my brain from the day I bought one myself, and then gave it away gratis to one of our french colleagues here, if I remember correctly. I just couldn't stand the challenge. But the design never stopped haunting me, so I recently bought the Grasshopper II, hoping to end it once and for all.

I'm hoping this thread will come to some sort of solution to this well known *rear suspension enigma* of these few types of Tamiya designs. I'd like to look at any possible variant of modification of these cars to improve their basic function, to suspend the body and dampen irregularities in the terrain surface.

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Last edit: by uncletom.

Grasshopper & Hornet - rear axle suspension 2 weeks 4 days ago #56110

Yep it is in France. :)
Traxxas did another system by using a like uniball system in the front of the gearbox .

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Grasshopper & Hornet - rear axle suspension 2 weeks 3 days ago #56112

Interesting, Sting. Can you show a picture?

To visualize the example in question, here's the Grasshopper II.



And nearest resemblance to this design that I can think of is the scooter. But the main difference between them is that the car has four wheels, its axle has a wheel on each side. A scooter has only one wheel, and no additional 'hornet pivot'.



And here's a small anim-gif of my Grasshopper II in slomo. Note that this is with clean new oil-less spring dampers. Once the car has been in sand and dust the dampers have much less movement.

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Last edit: by uncletom.

Grasshopper & Hornet - rear axle suspension 2 weeks 3 days ago #56117

Not sure if it is traxxas or panda. I have a doubt....

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Grasshopper & Hornet - rear axle suspension 2 weeks 2 days ago #56125

It was the Panda. Both the off-road racer and the Panda Stocker shared the same chassis which featured a plastic ball protruding from the gearbox which rested in a socket on the main chassis. I had both cars, and the friction shocks really didn't do any favors to the extra rear suspension articulation. As well, the plastic ball would eventually wear over time and make for a loose rear end. Heh heh.
The following user(s) Liked this: stingray-63

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Grasshopper & Hornet - rear axle suspension 2 weeks 1 day ago #56138

So there's not a good chance of doing any serious progress on this design? It is basically doomed from start to handicap an otherwise fine vehicle?

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Grasshopper & Hornet - rear axle suspension 1 week 6 days ago #56173

uncletom wrote: So there's not a good chance of doing any serious progress on this design? It is basically doomed from start to handicap an otherwise fine vehicle?


The Ampro gearbox mount makes these working so much better.
It will then make the axle twist like it should.
The mount act as a pivot point in the middle of the axle like the ball on the Panda cars.

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Grasshopper & Hornet - rear axle suspension 1 week 4 days ago #56192

I'm a big fan of Ampro Engineering and highly recommend his work if it is within your budget. An example of the extremes one can go to with the Grasshopper II/Hornet chassis:

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Grasshopper & Hornet - rear axle suspension 1 week 3 days ago #56194

Wow, I see that. Well, the Ampro thing is quite an extreme solution, it totally eliminates the original design. I really cannot imagine where the limit should be drawn between modifying, improving the original design, and simply rebuild the whole car into DT-02, or anything with four independent wishbones.

And here he has his new creation ready and running. Awesome car, but it's no Grasshopper or Hornet anymore.

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Last edit: by uncletom.

Grasshopper & Hornet - rear axle suspension 1 week 3 days ago #56203

The "ultimate" Hornet/Grasshopper is obviously independent suspension in 4 corners.
I would mention grahoo and his Grasshopper 4IS ( Grasshopper 4is (2002) , 2007 Grasshopper 4is ) which is the result of decades of modification. Of course AMPro has also spent countless hours and done a great job. On top, of course, it is great that everyone can get direct-fit parts and make the same car.
I have looked at a similar mod. The Hornet can accept a Frog gearbox and a pair of buggy arms with some construction work. In my opinion however it is a wrong direction, and I think The Hornet should keep its rear Pod in some form.

The Hornet slotted "rear axle stays" I consider just a simple and elegant change of The Grasshopper part to give the impression of the car having proper suspension :)
On a side note, I have looked around for real world examples of such rear suspension before. There are some small similarities with cars from the early 60's. It appears to me that if You convert the Hornet to single, centered rear wheel, move the motor to behind the right front wheel and shorten the car a bit, it will be brilliant, like the Peel P50 :cheer:

I have done a lot of stuff with my Hornet, but not thought any mod was a great enough improvement to write about...

Probably the most important then is my V-type 4-link setup to hold the rear "pod". It was inspired by the Ascari/Hatzenbach A12 pancar. It is called a RC Devil Mephyx now.
It is a bit tricky to get working on The Hornet without clearance issues. Some washers and nuts are near impossible to install, so not easy to change settings. Also the shocks may fight back by providing more friction if their angle is different from normal.
Oh, and the drilling for the bracket that hold the bottom of the V-links to the pod is very tricky.




I have also tried to run the car with a counterweight on the left side, to try to balance the car in jumps.
In this case a chopped off motor can on a spacer plate, filled with some sponge foam and a small brass weight.
Also at the same time with special 12mm outer diameter rear springs, plus custom 3d printed spring cups and lower shock mounts.
Then the friction from springs rubbing on the rear shocks was gone, but maybe lack of damping and short suspension travel came into play.
At least then it did not work well. Car appeared to jump straight, but rear end just flew sky high with rest of car following to crash site.


Another thing I have looked into is relocating the motor and using a multi joint cardan drive with telescopic ends.

In theory it can work. However it vibrates badly and can be dangerous if pieces of 5mm shaft fly off it at 20000+ RPM. I was lucky enough to only get hit in the thumb :-) Maybe it can be modified and run at lower speed, but in the simple form it is a risk of seeing Elvis singing Whole Lotta Shakin B)

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Last edit: by Notch.
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