Mechanical Brakes - RC-Monster Forums

Shark413 · 02:49 AM

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 in my opinion 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 brushless motor (or brushed) 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. 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.

tom255 · 04:15 AM

there are much simplier solution prefenting fall feigao to apart

And your buggy weight will be very high. Try to simplify things. Dp not use thick Aluminium, find solution for lightweight battery holders, and brake servo holder. Save some weight.
I was realy dissapointed first time of weight and handling of my truggy now I reassemble it again but try to save weight much as possible

Shark413 · 02.27.2008, 01:43 PM

tom255, thanks for the feedback, I like your motor clamps, were they handmade? And how do you adjust gear mesh? I agree about keeping things light, my buggy is over 9 lbs with a battery. Yeah my mount looks really thick because I wanted a big footprint (mount base to chassis) for strength and I do plan on milling it down and making it lighter. Is that a mini servo on your brake? how is it working out?

tom255 · 04:12 PM

Gear mech can be changed like in nitro motor, there are 4 streched holes on chassis, if you look carefully to pic you will see part of hole in chassis on rear clamp. Clamps made by CNC water jet cutter. But those clamps can be made any CNC Milling machine in any metal workshop.
Servo is standart in old design LSP servo posts made by water jet also but in new design i will use only ESC brake look how it work out, if it not satisfy me I will go for Low Profile servo. How i will attach I dont know it yet.

I made battery box from double sided PCB, Cut pieces by CNC router, weld it and reinforced it.

I hope in march I will finish my Truggy

Sparky · 02.27.2008, 04:17 PM

Here is what I did. I think it works good. I would have liked to use the back also.

http://www.rc-monster.com/forum/show...ushless&page=2

Shark413 · 02.27.2008, 04:51 PM

Tom255, that is a nice setup, fantastic fabrication work. I don't quite have the machining resources you do so I have to keep things pretty simple. I was thinking of doing the nitro type mount with the slotted holes for adjustment with a Mega Motor but since I have 4 feigao's laying around I decided to use them instead with a regualr endbell mount.

Sparky, that is one nice buggy. Very creative regarding how you handled the braking (ESC and mechanical). Very clean. I think I will go with the dual (front and back) mechanical brakes for now, and if that doesn't work out your ESC/Mechanical brake solution sounds very interesting.

On the battery tray, I am using Maxamp lipos, and they are good packs for the money. But they are a little fragile. The indivdual cells are not bonded together so under hard impacts they can slide around within the shrink wrap which distorts the pack and can rip the tabs off. That is why I don't just strap/velcro them to the chassis, which would be light weight but would not secure them enough for my needs. I have since taken my packs apart and bonded them so they should be more durable, and I may go back to strap/velcro only in the future to loose some weight.

Thanks guys for the great feed back, that's exactly what I was looking for.

Shark413 · 03.01.2008, 05:26 PM

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.

Shark413 · 03.03.2008, 02:37 PM

Setup my radio brake mixing on channel 3 and it works perfectly. When brake is applied by the radio the mechancial brakes activate, when throttle is applied the brake servo is neutral. ESC brake is set to zero. Can't wait to take it for a test run.

offroader · 03.03.2008, 10:47 PM

You can also use a Y adapter with your ESC and braking servo to do it too.

Shark413 · 03.03.2008, 10:55 PM

Hi offroader, yes I considered a "Y" harness. One issue is when you pull the throttle on your radio the brake servo will move to the on throttle position as well. More wear and tear on the servo. With brake mixing on channel 3 the servo does not move when throttle is applied. Thanks for the comments.

offroader · 03.03.2008, 10:57 PM

Quote:

Originally Posted by Shark413

Hi offroader, yes I considered a "Y" harness. One issue is when you pull the throttle on your radio the brake servo will move to the on throttle position as well. More wear and tear on the servo. With brake mixing on channel 3 the servo does not move when throttle is applied. Thanks for the comments.

Good thinking I never even thought of that extra wear on servo's I'm guessing it must draw extra power too. Thanks for the heads up.

lincpimp · 03.04.2008, 12:46 AM

Interesting mod there shark. I was going to do something similar with my ultra gtp. I would turn the servo 90 deg, so it sat sideways, with the brake cam closest to the center. That way there would be enough room for the pinion, and the body would not have to be altered (in your case, I have a sedan body). This would require making a new top plate, but that would not be too difficult, and it could be one piece.

RC-Monster Mike · 03.04.2008, 10:39 AM

The concept I envision would be a hybrid setup - mechanical rear brakes only, with a mini or micro servo, mixed into the 3rd channel. You could use a smaller servo by only using the mechanical rear brakes, and you could still effectively adjust front/rear bias completely with your radio. The motor and speed controller would brake the entire diff, and the rear mech. would obviously brake the rear. If you needed more rear bias, you could dial(mix) in more rear brakes on the 3rd channel, or dial out brakes on the 2nd channel(controller brakes).
This setup would save some weight, add some space, allow electronic bias tuning without leaving the driver's stand, and take significant load off the speed controller and motor during braking. I think this would be the best compromise between esc braking and mechanical braking - lighter than pure mechanical brakes and easier to tune, and more tunable than esc braking alone. :)

Shark413 · 03.10.2008, 09:58 PM

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.

jhautz · 03.10.2008, 11:20 PM

I tend to agree with you on this mechanical brake thing. I made this mechanical brake setup to test the Tekno clutch system on the buggy. I didnt really care for the clutch iitself in the end, but I did really love the mechanical brakes. The mini servo has plenty of power to lock up the tires on any surface I've tested so far and it has much more feel and adjustability than any of the motor brake setups I have had.

I just preordered the new Xray XB808 buggy and plan to convert it right out of the box. This brake setup is going on the new buggy, but I am going to flip the dif back around and use a standard pinion setup rather than the clutch.

It for sure adds weight, but I do much prefer the feel, and the mini servo doesnt add that much weight and gets its power from playing with leverage on the arm.

Ignore the Rx pack. I put it on there temporarily while I was waiting for a UBEC to come in.