Caster EX1.5r Based ROAR Legal 4wd SCT
05-08-2012, 07:13 AM
#1
Caster EX1.5r Based ROAR Legal 4wd SCT
Being the typical impatient racer most of us are, I decided to take having a Caster sct into my own hands. It is finally complete and I used it to win the opening race of the Factory Tracks Midwest Series this past Saturday.
With the ex1.5r coming in at 310mm wide on the spec sheet (and confirmed within a mm by measuring at the widest point with blank rims installed) a good 14mm must be removed to be roar legal. I went ahead and narrowed each side by 7mm by having new holes drilled in the rear arms at the hub and the excess arm and old holes cut off. The front arms were even easier, just lopping off the ends and taking a drill bit to the pivot ball holes and boring them a good 6-8mm deeper. It looks completely legit to boot.
For the CVDs, I had an older set from a prior ex1.5r that were 3-4mm shorter than the current ones installed all around and everything is kosher. They are literally .5mm from bottoming out in the diff outdrives throughout most of the suspension range, but hey, it works! With DE Racing sc8 rims and arms level, the track width is down to 295 with blank no tires mounted in the rear and in the front I can screw in the pivot balls to go as narrow as 295 before the cvd's bottom out. With tires mounted, the sidewalls pooch out to 297-298, but when going through tech the sidewalls give enough that they don't seem to care. Heck, I've seen a couple Kyosho's or slashes with the wrong rims on them (pushing them to 300+mm make it through. lol. Either way, it is close enough that when set at racing ride height with the arms a touch below level all around the car just rolls between two posts set at the ROAR limit of 296mm apart.
Parts list:
SC10 4x4 rear bumper
http://www3.towerhobbies.com/cgi-bin...?&I=LXBATS&P=7
SC10 2wd front bumper
http://www3.towerhobbies.com/cgi-bin...?&I=LXXCV9&P=7
SC10 4x4 body mounts
http://www3.towerhobbies.com/cgi-bin...?&I=LXBAPJ&P=7
Tekin Pro4 4600kv motor/RX8
Front shock tower had a couple corners sanded into the top so I wouldn't have to cut up the body mount and countersunk washers were used so the plastic captured by the shock mounts didn't deform too much. On the rear I was able to trim some plastic from the center of the body mounts rather than grinding the shock tower, but it weakens the mounts and I'll probably buy another set and just grind on the tower a mite. The outermost two holes on the tower and sc10 body mount line up perfectly.
For the front and rear bumpers, holes were drilled in the shock towers just inside of where they mount on the diff case. Plastic nuts were used as spacers for longer screws that went through the towers into the front and rear bumpers. A slight bend in the front skid-plate and boring out the stock holes allows the front two screws that go into the gearbox to capture it nicely. On the rear 3mm threaded holes were made in the 2.5 degree toe block for the rear bumper to mount on.
Ready to race, MINUS body, the car weighs in at 6 lb 10 oz. Current weight savings over my ex1.5r (that weighs 8lb even) come from ditching a pack, smaller motor, no esc tray, carbon fiber front deck/center brace/servo mount, no mud guards, material removed from the stock battery tray, plastic chassis braces, and plastic RC8 spur gear. The bumpers and body mounts perfectly cancel out the weight of the wing mount and wing that were removed.
For tuning I ended up at 35 wt oil and 1.2mm pistons in the front, soft kit springs, outer on the tower and inner on the arm. On the rear I have 25wt oil and 1.2mm pistons, RC8's softest rear spring (black?), second hole from the outside on the tower and outer on the arm, and no swaybar to start. Some limiters were added to the shock shaft to prevent cvd binding in the outdrive at full compression, but the lost travel is minimal. My initial diff oil guesses, that actually felt pretty good on the high traction track, were 7-7-3. Outdoors I might drop to 5-7-2.
Work that still needs to be done or things I would like to change are a custom rear sway bar, titanium turnbuckles for weight, and carbon fiber shock towers. The stock sway bar is way too thick for the lightened car and the mounting locations on the arm are so far out I couldn't find anything in the hobbyshop to work as a substitute. If you watch the video below you'll see I rolled twice, so I need to find some ~1mm music wire (stock bar is 1.8mm) to reduce roll a touch. I also have RCShox.com dual stage pistons on the way.
Here are pics and the youtube video of the main. Don't mind the pink body. It's my wife's and the only one I had on hand that lined up perfectly with the body posts. lol
With the ex1.5r coming in at 310mm wide on the spec sheet (and confirmed within a mm by measuring at the widest point with blank rims installed) a good 14mm must be removed to be roar legal. I went ahead and narrowed each side by 7mm by having new holes drilled in the rear arms at the hub and the excess arm and old holes cut off. The front arms were even easier, just lopping off the ends and taking a drill bit to the pivot ball holes and boring them a good 6-8mm deeper. It looks completely legit to boot.
For the CVDs, I had an older set from a prior ex1.5r that were 3-4mm shorter than the current ones installed all around and everything is kosher. They are literally .5mm from bottoming out in the diff outdrives throughout most of the suspension range, but hey, it works! With DE Racing sc8 rims and arms level, the track width is down to 295 with blank no tires mounted in the rear and in the front I can screw in the pivot balls to go as narrow as 295 before the cvd's bottom out. With tires mounted, the sidewalls pooch out to 297-298, but when going through tech the sidewalls give enough that they don't seem to care. Heck, I've seen a couple Kyosho's or slashes with the wrong rims on them (pushing them to 300+mm make it through. lol. Either way, it is close enough that when set at racing ride height with the arms a touch below level all around the car just rolls between two posts set at the ROAR limit of 296mm apart.
Parts list:
SC10 4x4 rear bumper
http://www3.towerhobbies.com/cgi-bin...?&I=LXBATS&P=7
SC10 2wd front bumper
http://www3.towerhobbies.com/cgi-bin...?&I=LXXCV9&P=7
SC10 4x4 body mounts
http://www3.towerhobbies.com/cgi-bin...?&I=LXBAPJ&P=7
Tekin Pro4 4600kv motor/RX8
Front shock tower had a couple corners sanded into the top so I wouldn't have to cut up the body mount and countersunk washers were used so the plastic captured by the shock mounts didn't deform too much. On the rear I was able to trim some plastic from the center of the body mounts rather than grinding the shock tower, but it weakens the mounts and I'll probably buy another set and just grind on the tower a mite. The outermost two holes on the tower and sc10 body mount line up perfectly.
For the front and rear bumpers, holes were drilled in the shock towers just inside of where they mount on the diff case. Plastic nuts were used as spacers for longer screws that went through the towers into the front and rear bumpers. A slight bend in the front skid-plate and boring out the stock holes allows the front two screws that go into the gearbox to capture it nicely. On the rear 3mm threaded holes were made in the 2.5 degree toe block for the rear bumper to mount on.
Ready to race, MINUS body, the car weighs in at 6 lb 10 oz. Current weight savings over my ex1.5r (that weighs 8lb even) come from ditching a pack, smaller motor, no esc tray, carbon fiber front deck/center brace/servo mount, no mud guards, material removed from the stock battery tray, plastic chassis braces, and plastic RC8 spur gear. The bumpers and body mounts perfectly cancel out the weight of the wing mount and wing that were removed.
For tuning I ended up at 35 wt oil and 1.2mm pistons in the front, soft kit springs, outer on the tower and inner on the arm. On the rear I have 25wt oil and 1.2mm pistons, RC8's softest rear spring (black?), second hole from the outside on the tower and outer on the arm, and no swaybar to start. Some limiters were added to the shock shaft to prevent cvd binding in the outdrive at full compression, but the lost travel is minimal. My initial diff oil guesses, that actually felt pretty good on the high traction track, were 7-7-3. Outdoors I might drop to 5-7-2.
Work that still needs to be done or things I would like to change are a custom rear sway bar, titanium turnbuckles for weight, and carbon fiber shock towers. The stock sway bar is way too thick for the lightened car and the mounting locations on the arm are so far out I couldn't find anything in the hobbyshop to work as a substitute. If you watch the video below you'll see I rolled twice, so I need to find some ~1mm music wire (stock bar is 1.8mm) to reduce roll a touch. I also have RCShox.com dual stage pistons on the way.
Here are pics and the youtube video of the main. Don't mind the pink body. It's my wife's and the only one I had on hand that lined up perfectly with the body posts. lol
| + YouTube Video | |
Last edited by Krio; 05-09-2012 at 09:22 AM.
05-08-2012, 08:52 AM
#3
It is definitely better in many aspects even with just two days of tuning (mostly between qualifiers no less. 
), but still three main reasons I'll be keeping my sc10 around. Biggest thing is acceleration. People always asked where the JATO booster was on my sc10, but being ~8 ounces heavier this buggy based truck doesn't quite "pop" like I'm used to. However, I didn't feel like I was giving anything up on the Losi trucks that made up the rest of the field. Secondly, 180 degree corners still benefit the lighter truck. The track in the vid didn't have a single corner I'd consider a tight 180. There were a couple 90 degree corners 4 feet apart, but not close enough together I could dive in, rotate, and punch out. Finally, a cautious reason will be picky tracks that won't allow conversions.
), but still three main reasons I'll be keeping my sc10 around. Biggest thing is acceleration. People always asked where the JATO booster was on my sc10, but being ~8 ounces heavier this buggy based truck doesn't quite "pop" like I'm used to. However, I didn't feel like I was giving anything up on the Losi trucks that made up the rest of the field. Secondly, 180 degree corners still benefit the lighter truck. The track in the vid didn't have a single corner I'd consider a tight 180. There were a couple 90 degree corners 4 feet apart, but not close enough together I could dive in, rotate, and punch out. Finally, a cautious reason will be picky tracks that won't allow conversions.
Last edited by Krio; 05-08-2012 at 12:21 PM.
05-08-2012, 11:25 AM
#4
Great job Chris. I do like this idea and the shorter CVDs really made it easy. If you think about it any PBS 8th scale car could do this if they just made CVDs shorter.
I do like the three diffs better than the belt on my SC10. I don't have the V2 center diff so I like my Jammin better right now. Has anyone thougth about merging the suspension of the SC10 4x4 with the Jammin drivetrain? I may give that a try!!
I do like the three diffs better than the belt on my SC10. I don't have the V2 center diff so I like my Jammin better right now. Has anyone thougth about merging the suspension of the SC10 4x4 with the Jammin drivetrain? I may give that a try!!
05-09-2012, 07:08 AM
#10
Thanks!
Your signature lists an SCTE. Any chance you know what it weighs rtr minus body? I've tried to follow the SCTE thread since it came out, but I'm drawing a blank on what a stock one weighs and what you guys have gotten them down to with different chassis, towers, etc.
Your signature lists an SCTE. Any chance you know what it weighs rtr minus body? I've tried to follow the SCTE thread since it came out, but I'm drawing a blank on what a stock one weighs and what you guys have gotten them down to with different chassis, towers, etc.
05-10-2012, 12:44 AM
#12
Tech Regular
iTrader: (12)
Thanks!
Your signature lists an SCTE. Any chance you know what it weighs rtr minus body? I've tried to follow the SCTE thread since it came out, but I'm drawing a blank on what a stock one weighs and what you guys have gotten them down to with different chassis, towers, etc.
Your signature lists an SCTE. Any chance you know what it weighs rtr minus body? I've tried to follow the SCTE thread since it came out, but I'm drawing a blank on what a stock one weighs and what you guys have gotten them down to with different chassis, towers, etc.
My racing Caster buggy made from EX1.5R Sport Roller with Carbon parts except towers ready to race weighted ~3.5kg... So I think that 3.1-3.2kg is achievable target for conversion...
05-10-2012, 05:28 AM
#13
Thanks for the info. My (reasonable) end goal is 6lb 6oz, but it will probably cost a pretty penny to get there. Titanium turnbuckles will probably get almost an ounce, I have one Hernanzez rear carbon shock tower in my pit box and it saves almost an ounce over the stock tower plus whatever weight savings come with using a smaller rear shock, there is more plastic that can be removed from the battery tray (already removed some), and as a last resort there is definitely aluminum that can be removed from the chassis. Anybody know a cheap machinist?
05-14-2012, 07:36 AM
#15
I would suggest anything over 50C and 5500mah for a 7 minute main just to be safe.
Last edited by Krio; 10-15-2012 at 09:15 AM.