frog rear suspension, any way to actually make it work?

[kaiser]

i've got a re-re frog, the wife got it for me for xmas a couple of years ago.
i built it stock, ran it, hated it and shelfed it, until this weekend.

i modded the front end with a set of wide arms i found in a parts box. i installed crp's shock tower and fitted some shocks.

here's what i ended up with:



it's nice and wide now.

i moved onto the rear and realized it takes so much pressure to get the rear end moving. i tried loosening the trailing arm mounts to free it up, no luck.

i think it was brandon g who had a frog at the vonats a couple of years ago. i wonder how the rear end was set up.

i'd like to try and run it at this years vonats, but the rear end is a real pia. it was also throwing dogbones left and right. i made some spacers to move the drive cups out a bit and that seemed to help.

so does anyone know how to get a frogs rear suspension to function smoothly?

[Mad Racer]

The Frog's biggest problem is the rear. Sure the front has no dampers but still works ok.

The rear on the other hand is utter rubbish, Both original and Re re.

I have spent many hours trying to get a good set up. Mt first Frog has Schumacher Cat 3000 front shocks with blue springs. This really made a world of differance.

I have since found a sey of Yeah racing shocks that work really well. It took a lot of time going through my Shock bin. To my amazement the red springs included are just right. Like my Shumacher set up. A wider front end will take steering away but more stable.

Yeah racing shocks, 70mm, Red springs, Pistons drilled with 2 1/16 drill bit. 30wt oil. Bolts straight on. Set with a little droop.

[kaiser]

i think the first thing i need to get is 4 70mm shocks.

the stock rears are so hard, it's tough to tell if i've made any improvments with them on there.

i like those yeah shocks, i have a few sets for my clod and they work very well.

as it is right now i can feel how the rear shocks are almost binding, it takes alot of pressure to get the initial movement.

[Coelacanth]

I read this an hour ago but wanted to withhold my opinions until other people chimed in. Now I can concur with Mad Racer. The Frog's rear-end sucked. My first RC was a Frog and I threw a lot of my hard-earned teenager money at the rear end, suspension, differential to make it work better--but no matter what, it still sucked.

A lot of us have fond memories of our first RC car, but mine were not. I was happy to sell my Frog and had no regrets. I was totally misled by the Tamiya Frog video ads back then, the suspension looked SO EFFECTIVE in those ads!

I think the biggest issue might be the position/location of the rear shocks themselves. The horizontal alignment and swing-arm design, with that upper tab, just don't transfer energy & absorb the suspension travel very well, it's too indirect. A more effective design usually involves near-vertical shocks with a much more direct, linear path of travel relative to the suspension arms.

[kaiser]

i know, it makes no sense that my hornet handles better then my frog.

live axle > frogs weird shock setup.

i am determined to make it handle better, even if i sell it afterwards.

[AscotConversion]

Set the rear shocks up like the JG blackfoot. There is another hole lower on the arm for a lower shock mount. You just need a vertical shock mount.

[kaiser]

i used to race a bf just like that bitd before stadium trucks came out.

the upright rear shocks will look really weird on a frog though.

i think i'm going to buy a couple of sets of short tamiya cva's and see how it is.
i'll get rid of the yeah racing fronts and put a black cva on each corner.

it's not even worth messing around with the stock rears right now.

[jwscab]

the shock position should not influence the performance of the suspension provided the lever is sturdy enough to transfer the motion without flexing. moving the fixed shock end up or down will affect the progression and spring rate, which can be adjusted. as long as the lever ratio is OK for the available springs.

I believe it's more of the crappy pivot system the frog uses, with plastic pins of large diameter in aluminum pivots. when they get dirt on them, they get 'sticky' because the plastic and aluminum are both soft.

the other gotcha is that if the body of the shock is lower than the pivot end, the air in the shock will sit right at the piston all the time at rest and will make the damping inconsistent.

[Coelacanth]

the shock position should not influence the performance of the suspension provided the lever is sturdy enough to transfer the motion without flexing. moving the fixed shock end up or down will affect the progression and spring rate, which can be adjusted. as long as the lever ratio is OK for the available springs.

I believe it's more of the crappy pivot system the frog uses, with plastic pins of large diameter in aluminum pivots. when they get dirt on them, they get 'sticky' because the plastic and aluminum are both soft.

the other gotcha is that if the body of the shock is lower than the pivot end, the air in the shock will sit right at the piston all the time at rest and will make the damping inconsistent.

I agree that the pivot system is a big part of the problem, but isn't that directly influencing the shock position? I don't think any system that requires a pivot motion will outperform a more direct up/down control arm-to-shock motion, because you're adding an extra unnecessary point of friction that you don't get with ball studs and ball-cups/ends.

EDIT: And true, I'm kind of contradicting myself because positioning shocks more vertically with the Frog suspension won't eliminate this unnecessary friction point. But still, I think the transfer of energy will be smoother when the shock pistons are more in-line with the suspension arm travel.

[jwscab]

nah, it's not the relative position of the shock. if you look at something like an F1 car suspension with the shocks inboard, and next to each other, the motion gets translated though levers and bellcranks.

the swing arm of the frog, provided it has a nice stiff strut, will exert the same force on the shock the same in that position as it would horizontal or vertical, the force is translated in position by the strut.

if you look at a standard A arm, the pivot point is a small 1/8" or smaller hinge pin. the bearing surface is the circumference of that pin, and very small in relation to the lever length of the arm.

alternatively, the frog has a much larger pivot inside and out, and the bearing surface is huge comparitively, and then on top of that, made of soft materials that create friction.

I added a quick and dirty pic. the 2 pictures are a swing arm, with 2 different shock positions. the lengths are the same (L), and the distance from the pivot to the shock is the same (x) and the relative angle between the shock body and line of motion is the same (a) the suspension would perform exactly the same in both instances.

[Mad Racer]

Well said.

The rear trailing arms are well designed. If there is binding there is some thing wrong.

Trailing arms offers great traction, due to no camber change through the deflection of the travel. The shock position is good and keeps the COG really low.

The springs are just way too stiff. That's all.
I raced my Frog with b4 and xxx in stock a few yrs ago. It had razor sharp steering (swb) pleanty of traction and was able to keep up in mid pack. ( 2.2 wheels and good tires)

Just better rear shocks really transforms this buggy to no end. Set right with a little droop it's the biggest single mod that has transformed any of my vintage runners.

[Coelacanth]

And yet, I can't recall a single race-winning offroad car with a shock alignment like that, off the top of my head....at least since the late 80's. Is it suitable for bashing, certainly. Is it an optimal design? I wouldn't think so. I can't even think of any 1:1 car with lay-down shocks. How can that shock positioning be so great if few (no?) winning cars use it?

I could be mistaken about offroaders that won races with Frog-like rear suspension, I was out of the scene for over 2 decades...

I was intrigued by your logic diagram. What it doesn't take into account is the differing nature of forces applied to the shocks. The lay-down shock + trailing arm combo relies on both up/down AND rotational motion to transmit force to the absorbers, which I'm sure--diagrams notwithstanding--is less efficient than a simple, direct, linear up-and-down force. (Keep in mind I'm not referring to swing arm vs. A-arm designs, just upright vs. lay-down shock designs--but the use of swing arms paired with lay-down shocks isn't an optimal design combo, IMHO.)

I'm just musing aloud, I'm a pretty logical, analytical person. Discussions like this always catch my interest.

[ROH73]

The Frog's horizontal, laydown shock positioning isn't any better or worse than having vertical shocks. Direct, approximately vertical attachment to the midpoint of the trailing arm gives the same result as having a horizontal shock attached to a strut over the pivot point. The geometry is different, but the results are the same.

The Frog's stock suspension fails because 1) the trailing arm is too flexible 2) the shocks are terrible 3) there is wear and binding at the pivot point (aluminum rubbing and cutting into ABS plastic). Address those issues, and the trailing arm works just as well as any other trailing arm, no matter the shock position.

No major race winning RC cars used laydown shocks because almost none used trailing arms (A-arms or H-arms just work better on most modern, i.e. post mid 1980s tracks). The last Championship RC car I can think of that used trailing arms was the Yokomo Dogfighter in 1985. It's tough to put laydown shocks on A-arm's because the shocks tend to get in the way of each other; they need to be stacked or side-to-side. The original Schumacher Cougar (I believe?) used F1 style bellcranks and inboard laydown shocks with A-arms in the front, but it was just extra weight and parts to break so the design was switched to more conventional upright shocks in later versions.

I would make a wild guess that street legal 1:1 cars don't use laydown shocks due to space constraints within the structure, not because of geometry issues. However, F1 cars, the most advanced racing machines in the world, use inboard laydown shocks, and they wouldn't have it any other way .

So, long story short, Frog stock shocks and flexible trailing arms = bad, laydown shocks = just fine.

[Coelacanth]

The Frog's horizontal, laydown shock positioning isn't any better or worse than having vertical shocks. Direct, approximately vertical attachment to the midpoint of the trailing arm gives the same result as having a horizontal shock attached to a strut over the pivot point. The geometry is different, but the results are the same.

In a sense that's exactly right, because no matter how the shock is mounted, you're still dealing with the Frog's flawed pivot points & trailing arms, no matter how the shocks are positioned.

Re: the aftermarket Jg Mfg shock towers shown by AscotConversion, do those therefore make no improvement to the Frog rear suspension?

[ROH73]

Re: the aftermarket Jg Mfg shock towers shown by AscotConversion, do those therefore make no improvement to the Frog rear suspension?

I have no idea; I've never used them. I do know the single biggest improvement to the Frog's rear suspension comes from using different shocks. I have Associated RC10 shocks on my Frog and Losi JRX2 shocks on my Blackfoot and both suspensions work well. I also know that switching out the aluminum side plates on the frog to the K3 and K7 plastic plates from the Blackfoot/Monster Beetle also helps a lot; much less wear as it's ABS plastic on ABS plastic.