One modification that I wanted to make to the Wraith kit build I did here on the blog is 4 wheel steering. Driving a rig with four wheel steering is extremely fun, especially on a scaler that will see a lot of technical terrain. So, I recently gathered all the parts I would need to make this mod. In this article I will cover the parts used and give a few tips for making this conversion as simple as possible. Let’s get started……
Parts list for 4ws conversion:
AX80073 – AR60 OCP Steering Linkage
AX30777 – AR60 OCP Servo Plate
AX30078 – Zero Ackerman Steering Plates
AX30780 – Wraith CVD’s
AX30760 – XR10 Aluminum Knuckles
AX30762 – XR10 Aluminum C-hubs
AX30450 – Steel Flange Pipes
AX80072 – Servo Post Parts Tree
AX30524 – Grey 91mm links
AXA1221 – 5x11mm Bearings
AXA1230 – 5x15mm Bearings
AXA1417 – Grey 5mm spacer for steering
AXA1428 – Grey 55mm standoff
AXA1331 – Steel Flanged Balls
AXA465 – M3x10mm Self tapping Flathead screws
AXA434 – M3x8mm Self tapping Buttonhead screws
AXA119 – M3x20mm Buttonhead screws
AXA115 – M3x10mm Buttonhead Screws (x3)
A few photos of the major parts required:
Steering plates for knuckles
Steel flange pipes
Steel flanged balls
Before we get started there are a couple things I need to mention. One, I stretched the wheelbase of this Wraith already by replacing the stock rear lower links with our XR10 94mm lower links. This moved the rear axle back just over 6mm, or about a 1/4″. To extend the upper links to match the newly lengthened lowers, I used our long curved XR10 rod ends at the chassis instead of the short curved rod ends. You can see the new lowers and longer rod ends on the uppers in this photo.
Another mod I made was to flip the plastic rear upper shock mount/chassis cross member upside down. This lowered the rear of my Wraith a little, which lowers the overall center of gravity. I also added a grey 55mm threaded standoff between the shock mounts for a little extra beef. I will explain why in a minute.
One thing I notice right away when I tried to mock the rear servo up, is the lack of uptravel in the suspension due to the servo case hitting the bottom of the tube chassis. The servo case hits the chassis almost immediately when you try to cycle the suspension. To fix this I removed the rear plastic lower chassis brace and replaced it with one of our 91mm grey lower links from the SCX10′s. I bolted the 91mm link into place where the widest part of the lower chassis brace normally sits. You could also cut the stock plastic chassis brace, and just use the long section to tie the 2 halves of the tube frame together. The aluminum link will provide a lot more rigidity though, so I went that route. Here you can see the brace I removed.
Look carefully and you can see the new 91mm link just below the upper links in this photo. Adding that 91mm link and the 55mm standoff between the shock mounts seems to replace any lost structural integrity from removing the stock rear lower chassis brace.
After the lower rear chassis brace is removed/replaced you can mount the servo plate to the rear axle and attach the steering servo. I am using Futaba’s S9157 servos for steering duties on both axles. Here is a shot of my rear servo and servo plate before installation. I used the short self tapping M3x8mm buttonhead screws to attach the servo tabs to the servo plate. I will use the M3x10mm self tapping flathead screws to tie the servo plate to the axle. Then, I will use the M3x10mm buttonhead screws to attach the servo to the tabs.
If you haven’t already, remove the rear wheels, drive hexes and cross pins. Next remove the rear plastic straight axle lockouts, and inner axle shafts. In order to remove the inner axle shafts, you will need to remove one of the screws holding the lower link/shock mounts in order to get the inner axles out of the housing. Replace the straight axles with the new CVD’s, attach the C-hubs to the axle, install the bearings into your steering knuckles, bolt the steering plates onto the knuckles using four of the M3x10mm buttonhead screws, insert the flange pipes into the knuckles and slide them into place over the C-hubs. Secure the knuckles to the C-hubs with four more M3x10mm screws. Then re-install the cross pins and drive hexes. Next we can install the rear steering link. One thing you will notice is the steering link has to be run upside down to clear the differential cover. Not a big deal, but you will need to drill the existing .100 diameter hole in the tie rod that the drag link secures too, all the way through the linkage. Then use one of the 5mm spacers between the drag link and tie rod with the long M3x20mm buttonhead screw to tie everything together. I will eventually trim the plastic boss hanging below the steering linkage, I left it there for now so people can visually see what I am talking about.
A shot with everything buttoned up and ready to roll. Don’t forget to re-install the M3 screws you removed to get the rear axle shafts out too.
Here you can see at full compression of the rear suspension, the servo sits perfectly in the rear cargo area without any interference from the chassis. Since I stretched the wheelbase a little, I did have to trim the cage a little where the plastic chassis brace attaches to the back of the tube frame. If you are still running the stock rear upper and lower links this shouldn’t be an issue.
One last adjustment I made was to zero out the caster angle in the rear steer to make life on the rear servo a little easier. To do this I added a 3mm grey spacer (Part# AXA1415) to the lower links at the rear axle.
It is hard to see in this photo, but the rear steering kingpins are now perpendicular to the bench my Wraith is sitting on. This means the caster is set to zero degrees. Adding positive or negative caster will put more stress on the rear servo, and it will struggle to center itself in hard binds.
Overall stance now…..
One thing to keep in mind when adding rear steer to any vehicle, you may need to add a Castle BEC to your system, depending on the torque rating on the servos you use they may overload whatever ESC you are running. I am sporting a Tekin RS Pro ESC, Tekin 10.5t motor, Thunder Power 5300mah 2S lipo and dual Futaba S9157 servos. To my surprise after driving for a few hours with this set-up, the ESC was only overloaded a few times while trying to throttle out of a bind and steering with both axles simultaneously. I am going to try and gear my Wraith down a little to help alleviate that issue. But, in order to have smooth performance at all times installing a BEC is the only way to go.
Another thing to keep in mind is you will need at least a 3 channel radio, with a 3 position 3rd channel switch, to have independent control of your front and rear steering set-ups. I am using my Futaba 4PK radio with my Wraith. The 4PK allows me to set the rear steer up for 5 positions, center, 50% right, 50% left, 100% right and 100% left. Some radios will only allow you to steer the rear from center to full throw left or right. Only a dual stick radio will give you full proportional control of both steering set-ups. Now, you can run a 4ws set-up on a 2 channel radio as well, if you use a Y-harness to plug the servos in to work together. But, that set-up will give you 4ws all the time, there is no way to control the servos separately. Just a few things to keep in mind before you dive into converting your Wraith to 4 wheel steer.