Is shock angle the answer for the Lunch Box?

[Saito2]

I've been studying the age old problem of the bound up Lunch Box rear suspension. Despite all the neat ways of properly locating the rear axle (3rd shock mod, etc.), the shocks are still on the "wrong" side of the axle. Motor acceleration simply pulls them to full extension, effectively locking them. The only way I've seen true improvement on this situation is by combining the better ways of axle location with a nearly horizontal rear shock like the DT-01 (Madbull, etc.). So, is it possible a more horizontal shock setup would at least bring the Lunchie up to par with the DT-01?

[TurnipJF]

To my mind, the troubles with the Lunchbox/Hornet rear suspension setup is that the gearbox can both pivot and rotate in line with the axle due to how it is mounted at the front. If front vertical movement is locked out DT-01 style by one of Pintopower's no-need-for-a-3rd-shock-mod braces for example, then the gearbox can only pivot. And once this situation is established, shock angle becomes far less of an issue.

 

The angle still affects how damping will alter through the course if the suspension's range of motion, but the gearbox will no longer be able to try to extend the shocks under acceleration. Normal forces will apply, the vehicle weight will transfer rearward under acceleration, and if anything, the shocks will compress rather than extend.

 

Well, those are my thoughts based on watching how my Mad Bull suspension reacts...

[kontemax]

The problem of the Hornet, Lunchbox, Grasshopper, Midnight Pumpkin series is not the rear dampers, this is a secondary problem.

The first problem of these models is the motor location, exactly the same problem of the scooters like the Vespa and similaria.

The motor is over the rigid axle joined with the wheels. This means that the motor, and its massive weight, is a part of the suspension.

The rigid axle is already a bad suspension without the weight, you can figure what happen if you put the more heavy part of the model on and eliminating that weight away from the chassis. De facto the suspension is made by the tires not by the dampers.

Everytime the rear axle bumps it has an enormous inertia due the weight of the wheels and the motor.

Another problem to have the motor over a rigid axle is the counter torque that is generated when you accelerate. In fact, if you will note, also the scooters rise up the rear end on acceleration because they have the same suspension scheme.

There's no way  to resolve this problem.

What you can do is to resolve the secondary problem, the chassis suspension. Over all this mess you also have another mass, that is the chassis, that receives bumps from the terrain. What you can do is to have a correct set up to absorb the bumps that arrive from the axle to the chassis, that is very light because the weight is in the wrong place.

The softer damper set up, related to the chassis weight, is the only solution but there are no softer enough springs to obtain this correct setup. If fact you don't have any sort of sag in the Lunchbox. The dampers position is totally wrong, and this is the 3th problem and you can move the rear dampers as you want but they will never work properly because their position is conceptually wrong. The problem again is the motor position that reduces the room for the rear right damper.

Max

[TurnipJF]

Valid points perhaps, but at the same time not quite what the OP was asking, at least as far as I understand it. While you are correct in saying that the Lunchbox has certain issues that occur as a result of its motor location and weight distribution, these are shared by other vehicles with the same basic layout, and that includes the DT-01. As I understand it, the OP was proposing that changing the shock angle could simply bring the Lunchbox handling to DT-01 standards, not solve all its issues altogether.

 

And to that question, while I believe that shock angle does indeed have a role to play in how damping changes through the suspension stroke, I also believe that the key area where DT-01-like improvements can be made is by securing the front of the gearbox in a DT-01-like fashion.

[Pintopower]

Great topic Saito2. I have been working on this a long time. Kontemax basically summed it all up. The motor is in the wrong spot and turns in the wrong direction. In fact, if you pull out the springs on a stock CW01 and then accelerate, the rear would rise and the truck would run as it usually would. 

I agree also with TurnipJF about the shock angle. As you lay them down a bit, the compression rate changes as the trans mount and the shock mounts do not revolve around the same axis. I have found excellent luck with moving the lower mount back to alter the angle. I just made some for the CW01 that I am excited to try./

The best fix by far is the securing the front of the axle by the 3rd shock which works well or a central pivot like this one I made:

I have made a double wishbone front end too but probably the best part of a CW01 is how bad it is. I mean yeah It hops and bounces and tumbles but think of how many cars don't do this. As long as that annoying trans slap is gone, i'm happy. 

 

[kontemax]

I believe that the 3th damper is useless and over engineered, the pivot is enough.

The other problem of the Lunchbox is the high COG that adds another issue to the model. Also the bigger rotating masses of the tires are another issue.

I believe that the Lunchbox is a total issue. We must switch the point of view.

For example a good warplane must be instable, yes, I mean instable, because this means that it has a great manouvrability.

The Lunchbox cannot be a stable model, if yes it will be no more a stunt vehicle.

 

Max

[MadInventor]

1 hour ago, kontemax said:

I believe that the 3th damper is useless and over engineered, the pivot is enough.

The other problem of the Lunchbox is the high COG that adds another issue to the model. Also the bigger rotating masses of the tires are another issue.

I believe that the Lunchbox is a total issue. We must switch the point of view.

For example a good warplane must be instable, yes, I mean instable, because this means that it has a great manouvrability.

The Lunchbox cannot be a stable model, if yes it will be no more a stunt vehicle.

 

Max

I agree with Max, the design is inherently flawed, you can put a lot of effort into making it a little better, but something like  a GF-01 or a Wild Dagger is going to offer far better handling out of the box By the time you've fixed all the issues you're going to end up with something like this, which retains the tires and the bodyshell :

 

[Saito2]

I bought a Madbull awhile back just to see/experience the rear suspension in action. It works pretty well for what it is, certainly better than a Hornet or Lunch Box. At this point my Lunch Box had the 3rd shock mod. After I got the Madbull, I modified my Lunch Box to mimic the pivot arrangement fount on the DT-01, essentially holding the rear pivot point locked in mid-slot location. It basically does what Pintopower's mod does. I always ran soft springs in the Lunchie's rear, soft enough that they were slightly compressed sitting still (if memory serves they came from the back of my departed Super G). Even with the new pivot, I would hear a slight slapping noise. Closer inspection revealed the shocks were slapping outward, to full extension when power was applied. So, in my mind, the pivot was only half the fix. This has led me to consider moving the dampers totally out of axis of the rotating rear assembly, like the DT-01 Madbull.

[Pintopower]

14 minutes ago, Saito2 said:

I bought a Madbull awhile back just to see/experience the rear suspension in action. It works pretty well for what it is, certainly better than a Hornet or Lunch Box. At this point my Lunch Box had the 3rd shock mod. After I got the Madbull, I modified my Lunch Box to mimic the pivot arrangement fount on the DT-01, essentially holding the rear pivot point locked in mid-slot location. It basically does what Pintopower's mod does. I always ran soft springs in the Lunchie's rear, soft enough that they were slightly compressed sitting still (if memory serves they came from the back of my departed Super G). Even with the new pivot, I would hear a slight slapping noise. Closer inspection revealed the shocks were slapping outward, to full extension when power was applied. So, in my mind, the pivot was only half the fix. This has led me to consider moving the dampers totally out of axis of the rotating rear assembly, like the DT-01 Madbull.

Yup, I just did that with a lower mount I made. So far, the truck feels better but I need nylon parts for actual testing (right now the parts are super brittle prototypes). 

[TurnipJF]

4 hours ago, kontemax said:

 

The Lunchbox cannot be a stable model, if yes it will be no more a stunt vehicle.

 

Max

Very good point!

[Saito2]

I still question if it was originally intended to be a stunt vehicle. When Tamiya bulked up the Mitsu Pajero for monster truck duty (as monster trucks were quite the rage during the Lunch Box's inception), they re-positioned the battery low and to the middle of the vehicle. They make no mention of it being a stunt vehicle in original US ads or MRC/Tamiya booklets unlike the earlier Pajero or Wild Willy. I theorize when they test drove the completed prototype, it still wheelied too much so a wheelie bar was added out of necessity. By this time, all the ad copy had been written so it was too late to plug it as a stunt machine. Even the box says "for racing and show". These are all just my theories and in no way guaranteed truth. 

[TurnipJF]

That may be the case, however to me the "For racing and show" indicates that it was indeed intended as a stunt vehicle, or at least one capable of stunts and normal driving.

 

To me, "show" implies showing off by means of performing stunts, rather than sitting on a shelf on show as a shelf queen.

 

Also just my opinion...

[Saito2]

I never thought of it that way. The Wild Willy and Pajero both had "stunt" in their description. I always took "show" to mean the Lunch Box's customizable nature (bodywork-wise) that was pushed in the ads and promos. However, I totally see how "show" could mean "showing off" (stunts) or "putting on a show".

[Flerbizky]

4 minutes ago, Saito2 said:

I never thought of it that way. The Wild Willy and Pajero both had "stunt" in their description. I always took "show" to mean the Lunch Box's customizable nature (bodywork-wise) that was pushed in the ads and promos. However, I totally see how "show" could mean "showing off" (stunts) or "putting on a show".

And by "showing off", you mean "rolling over". Mine does that a lot (:

[Saito2]

 Yeah, mine does that too. I had a dog that did that. I think it likes its belly rubbed or something.

[Prescient]

The problem as I see it is, this was designed 30 years ago to be cheap monster trucking (possibly intentionally wheeling) fun using a stock 540 motor and a msc; which it does perfectly out of the box. It wasn't even that cheap either then but relative to a Clod Buster it was.

A friend of mine runs one with CVAs, third shock mod and tamiya TZ SS and it's fine off road but can tip when it grips on corners on tarmac. 

The design is bang on for what it was meant to do. When this was designed the cost and availability of upgrades rendered mods pretty much irrelevant.

The issue is we expect it to be able to perform to modern standards with modern kit which it can't without some basic good value mods.

1) CVAs 

2) Lowered 10-15mm which eliminates the comical positive camber at the front and reduces centre of gravity.

3) Fixed / Stiffened rear pivot via 3rd shock mod or custom carbon/alu plate.

For a major improvement, you can easily build a plate set on the rear chassis / axle using 3-4mm carbon sheet to move the position of the dampers relative to the axel or even extend the chassis slightly.

Horizontal or vertical alignment makes little difference as the truck is never going to be a racing truck. With a fixed axle, I would suggest vertical though.