Four Wheel Steering BL Savage XL on 8S & 1521 - RC-Monster Forums

Finnster · **Four Wheel Steering BL Savage XL on 8S & 1521 -** 11.03.2009, 12:08 AM

I completed my mod for 4WS in my SavageXL. So far the list of goodies:

LST Shocks/RC Raven Progressive Springs
FLM Towers, Servo Plate, 2x drag link, servo mounts, lots of 4mm chassis braces, and eventually a skid plate
Neu 1521/1.5Y -1050kv
Kershaw Designs motor mount
MGM 9032 on 8S lipo
Custom oversized batt trays
2X 300oz Servos
40 series Mashers on 17mm Axial rims
Racers Edge Alu str blocks ($10/pr scored off ebay :) )
and of course a 45V UBEC

Basically I mounted a servo saver in the rear, as the F&R of the Sav is modular, so all the most of the necc holes already exist.
The rest of the mod involves cutting out part of the R chassis to clear the str rack:

Having to remove so much material, I reinforced the chassis with a cut up F shock tower from a GS truggy. I mounted this on the outside, but it would fit inside I just like how it looks. :) Plus it was only $1.50 on Amains clearance sale.

From there I mounted the servo to the inside of the TVP, and used a FLM 4mm chassis brace on for the top mount of the servo saver. There are a number of ways to do this. I finally decided on a method that left the servo up a bit higher and let the turnbuckle come down at an angle as a compromise of mounting ease, underside protection and rigid mounting. 2mm spacers were needed between the SS and the top brace, as well as some spacers for the servo mounts to clear some screwheads for the batt tray mounts.

Lastly I mounted the ESC aside the servo and mounted up the motor. The 1521 uses M4 mounting bolts, so I had to enlarge all the holes in the KD mount. I only did the L side to test, but I may do the R and move the motor above the ESC. I want to see how the ESC does with airflow first.

Underneath all this is where I will mount the FLM skid. I dont want a rock or stick coming up thru and striking the servo or the esc. The std skid plate should be about right, but may need some trimming. I also added 5x60mm turnbuckles from a hellfire, as well as the rod ends. Much tougher and tighter than the soft and sloppy stockers.

4WS was accomplished by using the 3Ch on my futaba Fasst radio and using the programmable mixing funct to tie to str channel. A trigger switch was programmed to switch between 2ws & 4ws on the fly.

So far I like it a lot (as you can see by the dirtiness of the truck ;) .) I tested the truck out and it ran great. Steers about as tight as my Hyper St truggy. It is a bit different however, as the pivot point moves forward towards the center of the truck. It will take some time to get all the alignments down. I may need a stiffer servo spring as well, the stocker seems to allow quite a bit of movement even when tight.

I'll have to get some video, but I stripped the plastic servo arm in front today climbing and leaping off mulch mountains.

11.03.2009, 02:15 AM

Very nice work man, you could rock climb with that thing now!

Those don't look like 40 series tires though...

JThiessen · 11.03.2009, 09:43 AM

The symmetry of the Savage almost beg's for a mod like this. Have you noticed any issues with servo timing? It would be ultra cool to be able to have a way to reduce the steering rate based on speed - which could possibly be done via motor rpm?

Slowkrawl · 11.03.2009, 10:03 AM

Jeebus that motor is huge in there! Looks good man, let us know how the 4ws works. My only worry is that at high speed it might roll and yard-sale your truck?

bruce750i · 10:25 AM

Quote:

Originally Posted by JThiessen

The symmetry of the Savage almost beg's for a mod like this. Have you noticed any issues with servo timing? It would be ultra cool to be able to have a way to reduce the steering rate based on speed - which could possibly be done via motor rpm?

Nice mods Finnster! In smaller r/c Helli's they use a 5in1 unit that proportions the tail rotor power with the main rotor power at adjustable rates instead of a gyro. hmm

Finnster · 11.03.2009, 05:10 PM

Quote:

Originally Posted by Freezebyte

Very nice work man, you could rock climb with that thing now!

Those don't look like 40 series tires though...

Trust me they are. The truck is just that big.

No where near like Chris's crawlers tho. Great for ground pounding and hill climbs tho.

Quote:

Originally Posted by JThiessen

The symmetry of the Savage almost beg's for a mod like this. Have you noticed any issues with servo timing? It would be ultra cool to be able to have a way to reduce the steering rate based on speed - which could possibly be done via motor rpm?

Its really easy actually to incorporate. There is no reason subtle design mods to aftermarket TVPs couldn't be made to make a rear SS a drop-in conversion. All that is really needed is a slight reworking of the rear section for turnbuckle clearance, and a couple mounting holes provided for for the steering rack brace and servo mounts. Would not interfere with standard config in anyway.

As far as servos go, no probs so far. Its mostly in radio programming. The R is setup to move just a fraction of the F, and this rate is adj. As far as spd sensistive steering, seems like some external hardware would be needed. Maybe the thing above would work. IDK. You can adj the exponential of the str to give a progressive feel to any str.

Quote:

Originally Posted by Slowkrawl

Jeebus that motor is huge in there! Looks good man, let us know how the 4ws works. My only worry is that at high speed it might roll and yard-sale your truck?

Eye, she's a mighty beast, that one. And to think I was once worried it would be too small.
As said, prob not what you want for real high speed antics, but any Savage seems a poor platform for a spd demon. It actually it is a bit less rollover prone so far as the rear end kicks out much more on turning and tends to slide more so than catch and flip. None the less, the Sav is just a hi-CoG platform and rolls far easier than say a truggy, and maybe even a Revo.

Gee · 11.04.2009, 05:32 AM

I put the 2sp tranny in my XL conversion today and was out back messing with it. Thinking I need a better turning radius on this puppy everytime I walked over to move it from where it was stuck (no reverse yet). The savage to me is a monster truck and should just be a big powerful beast vs the speed demon. This mod just seem to be a perfect fit for it. Nice work finnster. It's on my to do list now.

coolhandcountry · 11.04.2009, 04:08 PM

4 wheel steering is great.
I like it with a 4 channel radio with dual controls. :)

ilpufxit · **rear steer -** 11.04.2009, 06:12 PM

Quote:

Originally Posted by bruce750i

Nice mods Finnster! In smaller r/c Helli's they use a 5in1 unit that proportions the tail rotor power with the main rotor power at adjustable rates instead of a gyro. hmm

I put a gyro in my drift car and it makes me look like I know how to drive.

You could set up the rear steer to actually stabilize the truck! The gyro can make the rear end steer into a high speed turn but remain neutral at lower speeds. AND, you can dial the gyro gain in and out from your 3ch Tx. I'll have to think about how to switch it into full crawler-style 4ws as well. Wow, I'm stoked on this now, gonna have to add this to my list of improvements as I upgrade my blown diffs.

Bondonutz · 11.04.2009, 07:51 PM

Finnster,
Great MOD ! Would enjoy seeing video.

My Specktrum DX3S TX has only 2 channels POOP ! No 4W Steering for me.

Finnster · 11.30.2009, 01:47 AM

Finally got around to getting some video. Had a bit of time to play over the holidays.
Nothing too dramatic, just shows the steering action. Plan to do some more mods later to increase the str a bit more, but its not on the hot list.

[YOUTUBE]<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/3YmEnagHqX4&hl=en&fs=1"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/3YmEnagHqX4&hl=en&fs=1" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>[/YOUTUBE]

11.30.2009, 02:49 PM

Love the cyclone starting at 2:20!

suicideneil · 11.30.2009, 08:13 PM

Barely recognisable as a savy, the way it handles- rather epic...

Patrick · 12.01.2009, 08:14 AM

Just for fun set the rear up to steer the same way as the front, so you can make it crab walk everywhere.

You'd probably need to have the rear steer on the 3rd channel so you don't have to use it when you want to turn corners normaly. Would be interesting to drive if setup well.

Finnster · 10:53 AM

@Pat: That was one of my original plans to have crabwalking. I was going to do it by just rev the servo direction on CH3 on the radio, but I had to use the subtrim to center the servo perfectly. When I went to rev the R str, the trim offset moved too and messed it up. It looks like I would have to get the servo perfectly aligned in order to do this. I may work on it, but its a bit of a pain, esp w/ the motor right over the servo.
I may move the motor to the other side eventually, but I'm psuhing the esc a bit w/ the level of power, and I would need some small fans to ensure good airflow.

Also, my radio has a programmable switch that enables/disables the R str. Its kinda cool as you can hit it mid turn and see what a diff it makes. Meant to do it for the vid to demonstrate.