1/7 scale Traxxas

[hpiguy]

^^Yep, same issue I had with my Revos and Baja when new. My Wraith will also do it in high gear, but I'm not willing to sacrifice crawling performance to tune it out in that one.

 

[STANG KILLA SS]

if i want an apple, i dont grab an orange.:ror:


















~deep thoughts with stang killa

 

[MAC FAB]

its mostly because people dont tune them. the rear suspension are typically way to soft from the factory, and bottom out. my yeti did this. common sense would tell ya if its flying ass high to soften the rear springs for less rebound right?
did some slow mo recording to find out the opposite. rear was fully compressing on bug jumps, boTtoming out and then donkey kicking the rear up.

This post is priceless. The only way to tune the turd out of your rig is with slo mo video. TTs jump like crap (scratch built in particular) because of weight bias. Guys add a ton of weight to the spare to try to overcome it. Now your truck is real heavy. Back on track, you guys seen the RCCA video of the UDR running yet? Absolutely no torque twist whatsoever, even on 6s. Impressive. If I were to buy a larger scale truck, this is looking more and more like it. I've yet to buy any brand rig for anything, I'd rather build it. Waiting for some guys close to me to have them arrive, there is always a first for everything.

 

[STANG KILLA SS]

anybody have a pin to pin or hex to hex measurement on the UDR rear axle yet?

 

[JDM74]

Most notable for me is the subject of jumping.

Numerous threads here and elsewhere about how the yeti score and baja rey nose-dive off of jumps, and the struggles to 'fix' the suspension, with few understanding/admitting that the problem is that these trucks' trailing arm suspension is not good for jumping.

It is my impression that many bought for reasons of scale appearance, but then were disappointed that even though the score (or baja rey) looked like an SCT, it didn't jump like an SCT. :shrug:

I expect the same to happen with this truck.

The BR can jump you just need to know how to do it. My bone stock BR except for paint doesn't nose dive at all if you drive it right.

bashing 8-5-17-10 by JASON MCKIMMEY, on Flickr

 

[JDM74]

I've also found certain jumps are a lot harder to hit than others. It has to do with how long the jump face is. If the truck leaves the lip of the jump as the rear suspension is rebounding, it induces a forward rotation on the truck that must be counter acted by holding the throttle after the rear wheels have left the lip. I experimented with this in my back yard with several different height and length jumps that I put together with some plywood and blocks. It's actually pretty interesting.

My Losi SCBE jumps much differently (no surprise there since it is basically a SCT with a buggy body). I find myself having to apply brake mid air to bring the nose back down on most jumps. Face length and height don't have much affect on the rotation.

 

[MAC FAB]

All a matter of weight bias. Trailing arm rigs are nose heavy simply by design. For a test on that BR, zip tie a battery on the spare tires. Gonna jack up the spring rate but it will fly flat. 40/60 f/r weight bias works well, in 2wd anyhow on the gas. Full size has 350lbs+ in 2 spares and every bit of 100 gas of fuel. Either Traxxas told those who got to handle it first and run it to be vague, or they are clueless as to desert performance and don't know how to evaluate it. I'm leaning towards the latter.

 

[STANG KILLA SS]

yep the full size rigs shoot for 40/60 as well.

i remember a pic of one balanced on 2 jacks.

edit: found one, not the pic i remember but close enough

but its not all about weight bias. again proper 40/60, with too soft of rear springs/oil is gonna bottom out and still donkey kick ass high.

 

[JDM74]

yep the full size rigs shoot for 40/60 as well.

i remember a pic of one balanced on 2 jacks.

edit: found one, not the pic i remember but close enough

but its not all about weight bias. again proper 40/60, with too soft of rear springs/oil is gonna bottom out and still donkey kick ass high.

This helps. Both the Yeti and the Baja Rey have scale gas tanks that can be loaded up with weight to try to achieve the 40/60 weight bias. I believe the UDR also has a empty gas tank just sitting back there. It will be interesting to see how it jumps.

 

[JDM74]

So I just did a weight bias check on my BR (very crude, food scale and some blocks of wood to level the truck as it sat on the scale). Came in really close to 50/50 (50.2F/49.8R) with a 5000 Man battery in the slot. I figured it would take about 385 g or so on the spare tire to get it closer to 40/60 which is about the weight of the 5000 Man hardcase battery (good estimate Mac Fab!). The Traxxas has 2 spares back there as well as a bunch of scale stuff that adds weight so who knows, maybe it will jump better. I think being too soft sprung is a bigger factor than the weight bias.

 

[STANG KILLA SS]

I think being too soft sprung is a bigger factor than the weight bias.

yep. dont add weight, too many performance losses. tune the suspension

 

[MAC FAB]

You have to pick your battle, similar to a supercross bike vs the stocker. To work the track its stiff, beats you to death play riding. Full sizes sc trucks will suck in the desert when compared to an unlimited suspension rig, and vice versa.These rc rigs are the same. You want to jump, double your spring rate you have up front. You'll fly flat like superman. Don't sweat the oil, won't matter. Want to blaze the whoops, put the other springs back on, you'll be changing oil and messing with shock pistons if you take it seriously. Not going to do both well. Tune for what you do the most, be it a huck fest or blazen' through the rough. UDR is 2 shocks per wheel, tune 1 for compression, the other for rebound. Oh boy, I can hardly wait for that. Still gonna be a compromise with jumping and ripping the flats.
One more thing to consider. You want to jump, light truck. You want to haul the mail, add weight to the inside of your spares so its hidden and way back, tune the shocks for the new setup and be amazed, weight is your friend.

 

[DavidH]

The BR can jump you just need to know how to do it. My bone stock BR except for paint doesn't nose dive at all if you drive it right.

Indeed, as with the yeti score, you can mask the problem with driving technique, which only confirms that it is that much less suited to jumping than the SCBE.

From what little I could gather from their video, the UDR seems to kick up its rear axle when it gets the chance.

 

[DavidH]

All a matter of weight bias. Trailing arm rigs are nose heavy simply by design. For a test on that BR, zip tie a battery on the spare tires. Gonna jack up the spring rate but it will fly flat. 40/60 f/r weight bias works well, in 2wd anyhow on the gas. Full size has 350lbs+ in 2 spares and every bit of 100 gas of fuel. Either Traxxas told those who got to handle it first and run it to be vague, or they are clueless as to desert performance and don't know how to evaluate it. I'm leaning towards the latter.

What I was alluding to was the anti-squat geometry built into trailing arm suspension systems, like that on the yeti, that is (in part) responsible for the "donkey kick" behaviour. I don't know how much anti-squat is baked into the losi baja rey, or if it is adjustable as it is on the axial product.

http://www.rccrawler.com/forum/axial-yeti/537946-anti-squat.html

How To: Tune with Anti-Squat

You have to pick your battle, similar to a supercross bike vs the stocker. To work the track its stiff, beats you to death play riding. Full sizes sc trucks will suck in the desert when compared to an unlimited suspension rig, and vice versa.These rc rigs are the same. You want to jump, double your spring rate you have up front. You'll fly flat like superman. Don't sweat the oil, won't matter. Want to blaze the whoops, put the other springs back on, you'll be changing oil and messing with shock pistons if you take it seriously. Not going to do both well. Tune for what you do the most, be it a huck fest or blazen' through the rough. UDR is 2 shocks per wheel, tune 1 for compression, the other for rebound. Oh boy, I can hardly wait for that. Still gonna be a compromise with jumping and ripping the flats.
One more thing to consider. You want to jump, light truck. You want to haul the mail, add weight to the inside of your spares so its hidden and way back, tune the shocks for the new setup and be amazed, weight is your friend.

Indeed, but your heavy friend has to sit up quite high, and won't be so popular when you head into the corners. ;-)

 

[MAC FAB]

Indeed, but your heavy friend has to sit up quite high, and won't be so popular when you head into the corners. ;-)

Ride height depends on wheel travel. No need for a stink bug if there is some working room. Body roll is another story. If your Losi gets 3" out back, you're already in deficit mode. TTs tip around 5500 lbs if I recall correctly. Extra weight helps the suspension but will break rc parts just like the full size. 35" of travel out back and 26" +/- . UDR gets 4" out back, like 3-1/8" up front. Comes up short in my book for what it is, but has more than its peers. As the saying goes, no replacement for displacement, the same goes for wheel travel. Don't think they've scaled gravity yet. Then we're also money ahead, you'll have a million plus into a new TT.

 

[JDM74]

I would think TT's would run a small amount of anti squat so that under acceleration in the whoops the suspension would be able to work. Watching some videos of them and the amount of weight transfer they do during acceleration, I think that is the case. So what do you think the Yeti has, too much anti squat (>100%)?

 

[STANG KILLA SS]

UDR is 2 shocks per wheel, tune 1 for compression, the other for rebound. Oh boy, I can hardly wait for that.

that is impossible. requires valves/bypasses etc.

but yes to the rest of your post. cyclon mentions this when hes tuning his tube frame TT replicas. he has two totally different suspension setups for woops vs jumping."thumbsup"

 

[MAC FAB]

that is impossible. requires valves/bypasses etc.

but yes to the rest of your post. cyclon mentions this when hes tuning his tube frame TT replicas. he has two totally different suspension setups for woops vs jumping."thumbsup"

Not impossible, quite the contrary, you just need to think outside the box. "thumbsup"

 

[hpiguy]

that is impossible. requires valves/bypasses etc.

but yes to the rest of your post. cyclon mentions this when hes tuning his tube frame TT replicas. he has two totally different suspension setups for woops vs jumping."thumbsup"

Seems like that'd make for some long ass races when everyone has to pit before the rythym section every lap.

Also, someone mentioned a SX bike always being stiffly sprung. That's not always the case, and they were actually talking about this somewhat in Saturday night's race. It all depends on the rider and their preference at the end of the day, and there are trade offs to both too stiff and too soft setups. Windham was known for a softer than most setup, I have to think in part because of his super smooth style. Guy looked like he was never really trying hard, then there he'd be on the podium.

It's the same with RC rigs; you'll need to get a rough baseline for where you're running, then you can tune from there based on driving style.

 

[caleb.cole]

Not impossible, quite the contrary, you just need to think outside the box. "thumbsup"

One idea I just thought of is to do something similar to the MIP bypass1 shocks (currently discontinued) where there is a valve that blocks some of the holes on the piston and moves more or less depending on how fast the compression/rebound is. On one shock the valve could be under the piston, and on the other it could be above the piston, essentially making one able to be tuned for rebound and the other for compression using different thicknesses of valves.

http://www.miponline.com/store/media/myinstruct/mip-inst-01-496_p1.jpg