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Old 02-26-2008, 11:41 PM   #1
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Default Disc brakes on brushless buggy

I've had my brushless Kyosho buggy for almost a year now and I have been very pleased with it. It handles well, is blazing fast, pretty reliable and just plain fun. It is surprisingly competitive with nitro buggies with one exception, the braking. Don't get me wrong the motor brake is strong and can be finetuned via the MM ESC, but it still lacks the same feeling you get from a good mechanical brake setup. My biggest issue is that you cannot adjust brake bias using a motor only brake. So, I decided to mod my exisiting motor brake only buggy and add mechanical brakes. I search this forum (and others) for info and came up with design below. The issue is when using a standard brushless motor (or brushed) mount to power a nitro center diff equipped buggy the motor will not clear the rear disc brake or will not allow a small enough pinion to be used. Nitro cars have a long crank and a clutch bell that allows the engine to clear the brake. To get around this with a brushless setup I decided I needed to move the motor back about 6mm to get the necessary clearence. I made a new motor mount from scratch that attached to the chassis and placed the motor back enough to clear the brakes. The mount was made in such a way to fit very close to the center diff mount which allowed the use of smaller pinions. Since the motor mount was now no longer part of the center diff mount I was concerned with chassis flex causing gear mesh issues. But after looking at my overall design, the aluminum battery tray and special motor bracket (used to hold the Feigao endbells on) seemed to really keep the flexing under control. This buggy is still a work in progress, I still need to mount everything, construct a bracket for the brake servo, hook-up the linkage, setup my ESC and radio mixing, etc. But I wanted to share my project with all of you and perhaps get some constructive feedback. Sorry for the long post.



The problem, motor can won't clear the brakes. Pinion does not reach the spur.



Here is the rough motor mount taking shape.


The solution is to move the motor back.



Mount needs to fit close to the center diff.


With the motor moved back now the pinion reaches the spur.


Bracket to hold Feigao motor together also strengthens the mount/chassis.
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Old 02-27-2008, 05:55 AM   #2
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It looks very nice, keep us updated on how it works. That was my complaint with 1/8th electric is the lack of brake bias. Some tracks can really use it. The other option I was thinking about is a one-way. Someone should make one.
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Old 02-27-2008, 08:01 PM   #3
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It looks very nice, keep us updated on how it works. That was my complaint with 1/8th electric is the lack of brake bias. Some tracks can really use it. The other option I was thinking about is a one-way. Someone should make one.
Dan from RC Product Designs has a one-way design for the 1/8th brushless conversions. He's just trying to get caught up with all the new integrated splash guard battery trays for all the kits before he makes them.
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Old 02-27-2008, 11:17 PM   #4
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Hey guys thanks for the feedback. Somebody asked why I went so big on the mount (thickness). The reason I went with such thick aluminum for the mount was because the motor is very long and heavy and puts alot of stress on the mount where it connects to the chassis. I wanted a large footprint to get maximum support. But looking at it now with a rear support brace I probably didn't need to go so thick. I will either fab another mount that is not as thick or let the aluminum termites loose on the big mount and lighten it up. One of the biggest issues with a motor only brake is with a center diff there is slippage and inconsistancy between the front/rear as the center diff does it's thing. With mechanical brakes once you get them setup they are very consistant and easily adjustable.

But you guys have me stumped with the one-way. How does a one-way bearing work related to braking? My Brushless Revo has a one-way bearing in the tranny and so the mechanical brakes must be used, because the tranny freewheels when there is no power or motor braking is applied. How would a one-way be used to control front/rear braking bias?
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Old 02-27-2008, 11:26 PM   #5
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hmmm
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Old 02-28-2008, 06:22 AM   #6
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Originally Posted by Shark413 View Post

But you guys have me stumped with the one-way. How does a one-way bearing work related to braking? My Brushless Revo has a one-way bearing in the tranny and so the mechanical brakes must be used, because the tranny freewheels when there is no power or motor braking is applied. How would a one-way be used to control front/rear braking bias?
The oneway will typically replace the front differential. I'd guess that's what Dan has designed. It will take a huge load off of the motor during braking as now when you apply the brake only the rear wheels will be braked. The front wheels will roll free which will greatly increase cornering capability and make the car drive like a 2 wheel drive vehicle when not on power. On Power you will basically have a locked spool in the front.

Now I'd like to see someone come up with a front one way shaft input so I could keep the differential up front.
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Old 02-28-2008, 08:55 AM   #7
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I'm sorry, I must have had a brain fart last night....LOL

Dan is working on a center slipper to replace the center diff. You'll be able to make quick adjustments on the center slipper which will affect the braking just like if you changed the center diff fluid.
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Old 02-29-2008, 12:43 PM   #8
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ok, that makes more sense. I am familar with a one-way bearing for the center or front diff in 4wd 1/10 buggies, bascially it engages when power is on and freewheels when brake is applied. In my case I would want the ability to dial in or out brake to both the front and back brakes to finetune the "feel" and for changing track conditions.
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Old 03-01-2008, 02:24 PM   #9
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I had some free time last night so I was able to work on the buggy. I was able to mod a stock aluminum radio tray to fit over the carbon fiber tray. I added another tray post to support the end of the tray. This holds the brake servo, which I test fitted and everything looks good. One issue, since the brake servo is a little more outboard than normal the linkage hit the body slightly, I remolded the body to create a small bubble to allow clearence for the linkage. I am waiting for longer linkage rods to actually hook up the brakes. Then I will setup the ESC for zero brake, use channel 3 brake mixing to control the mechanical brakes and hopefully be able to test it at the track next weekend.


Test fitting the servo and linkage




Additional support post added.


Body before remolding.


Body after remolding, added a small bump to clear linkage.
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Old 03-04-2008, 01:58 PM   #10
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Got the channel 3 brake mixing setup and it works perfectly. With the ESC set to zero brake, when you press brake on the radio the servo applies the brakes, when you go to neutral or power on throttle the brake servo stays in neutral. This is exactly what I was looking for, adjustable brake bias and the added benefit of removing a huge load (motor braking) from my ESC/Battery. I ordered longer linkage but it was the wrong size. I reordered and as soon as it arrives I will hook it up and start finetuning. I have just been spending the time drill/milling parts to lighten it up, lost several ounces from the battery tray and motor mount.
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Old 03-10-2008, 08:45 PM   #11
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I got the buggy out to the local track and ran several packs thru the buggy. The mechanical brakes worked perfectly, strong but with great modulation (feel). It made the brushless buggy handle so much better, my poor Kyosho 777 SP2 nitro buggy hardly got any track time. Having run this buggy with motor brake only, for a long time, all I can say is I would never run a 1/8 scale brushless buggy on motor brake again. The difference is unbelievable.



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