Mechanical Brakes on Brushless Buggy

[shark413]

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.


http://i142.photobucket.com/albums/r115/shark413/problem.jpg
The problem, motor can won't clear the brakes. Pinion does not reach the spur.


http://i142.photobucket.com/albums/r115/shark413/rough.jpg
Here is the rough motor mount taking shape.

http://i142.photobucket.com/albums/r115/shark413/solution.jpg
The solution is to move the motor back.


http://i142.photobucket.com/albums/r115/shark413/clearence.jpg
Mount needs to fit close to the center diff.

http://i142.photobucket.com/albums/r115/shark413/itfits.jpg
With the motor moved back now the pinion reaches the spur.

http://i142.photobucket.com/albums/r115/shark413/brace-1.jpg
Bracket to hold Feigao motor together also strengthens the mount/chassis.

[ducati777]

thats cool.

[rccardude04]

Very cool. I was thinking about possibly doing a BL buggy at some point but was worried about the brakes. I figured I'd try to keep the mechanicals but everyone tried to talk me out of it. I guess it depends on driving style as to which one is really better.
At least they will be more consistent now... No more oil to contaminate them :D
-Eric

[Cotharyus]

I'm _absolutely_ using mechanical brakes on my brushless MGT, however the layout dictates that no challenge such as this exists for that set up. Anyhow, I agree that with something large like a buggy or a monster truck, mechanical brakes are a must. That motor mount you made - that is one sick looking chunk of metal! I like it though.

--
Cotharyus
http://cotharyus.net

[shark413]

Guys thanks for the feedback. The reason I went with such thick aluminum for the mount was because the motor is very long and heavy and puts alot ot 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.

[GSMnow]

The braking on the Mamba Max ESC is very adjustable as well. Would you dial it all out, or use them together? In my thinking, having the motor braking supply 1/2 the stopping power could theoretically double the life of the friction brakes. You might even be able to use softer springs from the servo to the mechanical brakes, so it would be even smoother and easier to adjust.

The little time I have been able to test my buggy, with motor brakes only, I can see where front friction brakes could help. The rear would get light into a turn while braking, and the inside rear tire actually turned backwards a bit. Obviously, The front tires are getting less brakes than they could take. But I was thinking, I may not need rear mechanical brakes at all. With the front using friction, the motor is then braking just the rears.

This is all just theory, as I have only driven it with motor brakes only, and with just a big brush motor that only hit 25 mph. My Spektrum DX3.0 is a 3 channel system with one of the choices being "brake mixing". I have not tried it yet, but I assume it only uses the third servo in the brake direction. It would be nice not having to deal with the forward motion.

[GordonFreeman]

Not to hijack but here is my experimental solution to the brakes problem:
http://www.nitrokillers.com/showthread.php?t=457

[GSMnow]

My brother and I actually drew up sketches of a setup with separate front and rear motors like that. To get a bit of flexibility in the motor rpms, we decided to still use pinions and spurs. The motors would have ended up basically side by side. The shaft ends sticking forwards. The spur gears would have been right next to each other, with the front motor having the gear extend out a bit further to reach. We never actually built it though. The cost of 2 Neus and a pair of Mamba Maxes just added up too fast. With the extra gear reductions in there, we figured something like a 1512 for the rear and a 1509 for the front. Winds and ratios were not chosen, but it was quite obvious the power was far more than needed and the cost was just silly. Either motor alone has enough power, so I went back to a single motor and center diff, still waiting for a Mamba Monster Max.

I am certainly looking forward to your performance results. The engineering is very sound, and it should out perform any normal drivetrain as long as the weight is not killing you.

[shark413]

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.

http://i142.photobucket.com/albums/r115/shark413/side-2.jpg
Test fitting the servo and linkage

http://i142.photobucket.com/albums/r115/shark413/top-9.jpg

http://i142.photobucket.com/albums/r115/shark413/traybrace.jpg
Additional support post added.

http://i142.photobucket.com/albums/r115/shark413/bodynobump.jpg
Body before remolding.

http://i142.photobucket.com/albums/r115/shark413/bodybump.jpg
Body after remolding, added a small bump to clear linkage.

[shark413]

Set up the 3rd channel brake mixing last night and it works perfectly. When you press brake on the radio the servo brakes, when you apply throttle the brake servo just sits in neutral. I ordered longer linkage rods, and they arrived yesterday but were the wrong size. I reordered and as soon as they get here I will hook up the brakes and start finetuning them. For now I have just been drill/milling parts to lighten everything up. Was able to shave a few ounces off the battery tray and motor mount.

[shark413]

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.

http://i142.photobucket.com/albums/r115/shark413/top-10.jpg

http://i142.photobucket.com/albums/r115/shark413/side-5.jpg