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  1. #1
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    Question Has anyone tried Pro line extended A-arms on xo-1

    Hello,
    Has anyone tried Pro line extended A-arms on xo-1.
    Long story short I'm doing the Leopard 5882 with 36t pinion that normally requires you to flip the right with the left a arms so the shock moves to the rear so it clears the the pinion.
    But I noticed the proline extended arms have a hole for the bottom of the shock slightly further out which allows the shock to stay in the front and still clear the pinion.
    The only issue I see is that the wheels extend just beyond the body. Maybe 1/8" of an inch.
    Is this a problem in your opinion?
    Or is there a way to tuck the wheel in with a shorter wheel hub?

  2. #2
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    If you look at my build under "is it worth building" you will see that the rear shock tower hangers can be cut in half and you will have no problem and no need to flip anything... check it out...

  3. #3
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    Thanks XO-1 MD. I have seen it, which is a third choice for sure.
    1. Flip the arms
    2. Cut the shock hangers
    3. Pro line a arms which comes with increased wheelbase.
    Which could be a side benefit in of itself. I've been trying to research what it might mean for stability. Long story short RC cars have a wheelbase/track ratio that is ridiculous to begin with compared to real cars. Which seems to strive for a 1.618 ratio, some call the golden ratio.
    The xo-1 already has a 1.34 ratio. Which would mean that it should be narrower. Not recomending it.

    What I can do is use the e-revo wheel hubs which are shorter than the Xo-1 hubs so it will pull it back in.

  4. #4
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    So I went with choice 3. Pro line arms with the E-revo wheel hubs. The arms pushed the wheels out about 6mm but the shorter hubs pulled them in 4mm.
    The extra hole allows the clearance for the shock and 35t pinion. Could maybe get away with a 36t pinion. Not sure a 37t would make it. This is with the 46t spur.




    Just ran it for the first time but only with a 4s. Wow! Easily hit 70+ mph.
    8s is going to be insane.
    Last edited by Double G; 01-24-2015 at 12:29 AM. Reason: merge

  5. #5
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    What I'm worried about running pro trac arms is that your driveshaft's splined contact become less and running 8s is something I'd be worried but if you get a longer outer male splined #6752 it'll bring back in 4/5mm contact. Did you bore the end of the revo adapters for the retainer?
    Last edited by Pedro Penduko; 01-24-2015 at 02:16 AM.

  6. #6
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    They make a adapter to put on the spur gear to lower the size of the gear then there is no need to flip the arms, or make them
    longer.

  7. #7
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    Thanks for the tips on both the 6752 and boring out the revo adaptors. I'll do both.
    I can't try running this car now with all the snow and salted roads.

    I haven't seen an adapter for the XO-1 spur. Do you have a link?

  8. #8
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    Quote Originally Posted by neows6 View Post
    I haven't seen an adapter for the XO-1 spur. Do you have a link?
    He's probably talking about guys on YouTube using Robinsons racing slipper clutch which only allows you to use RR metal gear designed for that clutch assembly.
    Last edited by Pedro Penduko; 01-25-2015 at 08:24 AM.

  9. #9
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    I use the PL arms with the mentioned mods(6752 shafts, summit hubs counter bored, reversed rear arms) with zero problems. In the process of major suspension mods for better (I hope) wheel control at extreme speed.
    Ok a short story now. I've seen many people add ALOT of weight to the front of there XO-1 to keep it from blowing over. This to me just didn't seem rite. I've been around racing rc cars since before Traxxas even existed and since their introduction into the rc world, and as an engineer myself I have watched their progression and their engineering get better, and better, and better to the point that I had confidence in the job they did on the XO-1 to be able to run at 100+mph without added nose weight. With a very nice wind tunnel in front of my house called U.S. Highway 40 in the country I proceeded with my testing and found she could lift off well but flew like a turkey and landed as such. So with some help from 2 great friends and a couple of cameras we ran it and video it to review what was going on at lift off. What was revealed was the rear was completely bottoming out and the front suspension was able to lift way to much creating an angle of attack that would definitely make her air born. So to work I went and used some old rc carpet car tricks when no droop screws are used. Good ole silicone fuel line added to the inside of the front shocks to limit down travel and on the outside of the rear shock shafts to limit compression. This allowed me to hold the recommended ride height front & rear at speed and low and behold it confirmed that I knew the gentlemen at Traxxas did their job. It stays on the ground with no added nose weight and with SLOW steering drives quite nice at 100+mph, it does require warm pavement though.
    I want to say thanks Traxxas for your products and work!!

  10. #10
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    Thank you for the tips! I'm just waiting for the snow to melt now. In a way I'm glad I'm moving slow as I'm learning from you guys.
    What length of tube did you use?

  11. #11
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    Also what ride height did you settle on?

  12. #12
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    I used 15mm in the front and 18mm in the rear for ride height. The tubing length is car specific because of the shock locations and tubing differences.
    Traxxas is not specific on where to set these ride height measurements so I used the axel center lines. I believe the design angle of attack is 3mm- thus the difference 18mm-15mm=3mm.
    If you take a good look at your XO-1 from the front and rear at ground level or put a strait edge across the bottom from side to side you will notice its not flat at all. This has purpose and has ALOT to do with how the ground effects work on the XO-1. In under chassis ground effects you need air under the car and you need to control the air under the car. The rear diffuser does nothing if it has no air feeding it. In full size race cars its done with channels from front to rear most of the time. On our RC cars we run into room problems and from what I see in the XO-1 the whole bottom of the car is used as the channel to feed the rear diffuser. The front splitter captures the air and with the smallest area between the chassis and the ground at the front axel it conditions and accelerates the air to the progressively bigger area under the middle of the chassis which lets it slow down, starts expanding and it has a decrease in pressure. This continues to the rear diffuser where the air speed and pressure is the lowest, and the expansion and down force are the greatest. I think they did great job on the aero package but the chassis needs upper control arms for what the car is really capable of.

  13. #13
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    Again thanks for the tips. I have an ever 12 and 12 mm I built it from scratch so I didn't have a stock value to go by.
    My thought would be that the diffusers job is to speed the air up as it exits the rear in the that Bernoulli principal effectively creates an upside down wing. From what I've read a proper real race car can generate up to 60-70% if the overall down force this way.
    I was thinking and maybe incorrectly if I lowered the front much more than the rear the sir would be compressed upfront therefore speed up and there in reduce the overall effect of the air entering the diffuser.
    But again I need the snow to melt and the salt washed away before I can do any test runs. I wouldn't be doing full speed runs immediately anyway.
    So I'll experiment with both the chassis attitude and the extent of the down travel.

  14. #14
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    You are correct that it still uses the Bernoulli principal which leads to the use of Reynolds numbers for air foil shapes which differ drastically when one surface has no boundary layer(top of vehicle) and the other does(bottom next to road surface). Ill explain more after work.

  15. #15
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    She's ready to go.


    But I can't keep up with the snow....

  16. #16
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    Quote Originally Posted by neows6 View Post
    But I can't keep up with the snow....
    It looks like you could use a larger rig...or a few more!
    "Happiness depends upon ourselves." -Aristotle

  17. #17
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    No pun intended but that's cool!

  18. #18
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    Or I need to move to Florida. It could be worse I guess I could be in Boston. Don't temp me if I bring home another Traxxas my wife will divorce me. Lol.

  19. #19
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    Quote Originally Posted by bn2o View Post
    I use the PL arms with the mentioned mods(6752 shafts, summit hubs counter bored, reversed rear arms) with zero problems. In the process of major suspension mods for better (I hope) wheel control at extreme speed.
    Ok a short story now. I've seen many people add ALOT of weight to the front of there XO-1 to keep it from blowing over. This to me just didn't seem rite. I've been around racing rc cars since before Traxxas even existed and since their introduction into the rc world, and as an engineer myself I have watched their progression and their engineering get better, and better, and better to the point that I had confidence in the job they did on the XO-1 to be able to run at 100+mph without added nose weight. With a very nice wind tunnel in front of my house called U.S. Highway 40 in the country I proceeded with my testing and found she could lift off well but flew like a turkey and landed as such. So with some help from 2 great friends and a couple of cameras we ran it and video it to review what was going on at lift off. What was revealed was the rear was completely bottoming out and the front suspension was able to lift way to much creating an angle of attack that would definitely make her air born. So to work I went and used some old rc carpet car tricks when no droop screws are used. Good ole silicone fuel line added to the inside of the front shocks to limit down travel and on the outside of the rear shock shafts to limit compression. This allowed me to hold the recommended ride height front & rear at speed and low and behold it confirmed that I knew the gentlemen at Traxxas did their job. It stays on the ground with no added nose weight and with SLOW steering drives quite nice at 100+mph, it does require warm pavement though.
    I want to say thanks Traxxas for your products and work!!
    This is some of the best info I have read on here in awhile. A lot of us thought along the same lines when we switched the stock springs out and put stiffer ones in the back. With an 8s setup in the car, the added weight from the larger motor and batteries made it less likely to flip also, well as long as you didn't hit something in the road to cause the car to go flying.

    Good info.
    XO-1 #4...

  20. #20
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    I see I wasn't quite clear in my above post.( This continues to the rear diffuser where the air speed and pressure is the lowest, and the expansion and down force are the greatest.)
    When a substance flows through a path and its cross section in its path changes to a bigger cross section, it has no choice but to slow down. With a liquid(water) that does not compress or expand it shows up plane as day, but with a gas(air) it can compress and expand. When the gas expands because of an increase in cross sectional area it slows down, expands and the pressure lowers.
    A different way of looking at it is if you take a 5 gallon bucket and attach your garden hose to the bottom of it. Now turn on the water and start filling it up. Inside the hose you have a higher flow rate and inside the bucket you have a low flow rate because of the cross section differences between the bucket and the hose. The only way for it to fill the bucket at the same rate as the hose is fill is for it to expand which lowers the pressure. Thus if you lower the pressure under the car even without increasing the pressure above the car you gain an increase in down force.

  21. #21
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    The lower pressure at the diffuser pulls the vehicle in a direction normal (perpendicular) to the diffuser surface. The force produced has a large component in the vertical direction that increases the force on the tires (more traction) and a drag component that results in some aerodynamic losses. Even on the rear wing, it is the bottom surface that it crucial for producing down force. Hopefully this helps convey what bn20 is trying to say.

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