Converting a GST 7.7 to brushless. Help?
 

Hey. I'm going to convert a GST 7.7 to brushless. The car weighs approx. 17 lbs with the nitro gear. Not sure what it will weigh after the conversion is complete, but I'm guessing around 17lbs. I'm planning to run a Castle Creations 1717 @ 1580kv on 6s lipo with a Mamba Monster Max. It looks like the 1717 is the most powerful motor I can run on 6s on a MMM ESC.

But I need some help (This is my first electrical conversion.)

These are my worries;

This is a car with 2 clutch gears and 2 spurs for gears. I guess it's possible to mount a 2 speed clutch system on a 2 speed pinion adapter, like this; http://www.rc-monster.com/proddetail...adapter&cat=40

This tranny also houses the reverse, which is done by a servo via remote. How will this work with an electrical setup? I'm guessing the tranny needs to be in reverse in order to go backwards, and if I just hit reverse with the motor the tranny will pretty much go bye bye.

Also, there is no slipper clutch currently installed.

How do I solve these problems for a brushless setup? If getting a 1 speed tranny/Direct drive is the easiest solution, which should I get? Or can I just strip down the GST tranny and place the motor directly on the center diff somehow? I've seen what looks like this setup in lots of GST brushless pics. Or can I just mount the motor directly onto the spur gear like the nitro setup somehow?

Basically, what is the easiest way to get this car moving with an electrical motor? How do I get the motor mounted onto the tranny?

Whew.. lots of questions!

Thanks in advance.. :P

That 2 speed won't stand 10 seconds under a 1717 , so ditch second gear. Lock it in first and ditch reverse also. I doubt the motor and esc would work well as brakes on a truck that size so i hope you plan on mechanical braking right? For mounting the motor your best bet is probably to make a custom motor mount out of some angle or see if mike can whip you up something. I've never really seen a GST 7.7 up close so I'm just kinda spit balling here.I'm sure someone else can give you a more detailed answer.--Josh

Yep, mechanical braking. Haven't done this before, so I need to find a tutorial on mechanical brakes hen I've gotten the components (Next week I guess.).

Here's a couple of pictures of a converted GST. It looks like the guy removed the tranny and just used the center diff spur;

Attachment 9159
Attachment 9160

This is a pic of a conversion WITH the tranny;

Attachment 9157

This guy uses all the gears, and according to him it's working fine:

http://origin-images.rcuniverse.com/...97/Tq48930.jpg

The first 2 look rather well set up. The 3rd one not so much. I wouldn't listen to/ go off anyone elses design who mounts a lipo to the top of there cage,WTF?--Josh

Hehe, it looks a little weird indeed. :p

But what would be the simplest way to mount this up? Would it be to strip the tranny down to the center diff and use that, or just use the entire tranny without reverse / second and third gear? Or buy a direct drive system?

I would like to install a slipper clutch as well.

E-maxx, Revo, Savage, etc (the popular trucks) all have simple direct drop in upgrades for brushless @ RC-monster, but I'm not sure what sort of hopup would relate to this setup. I don't have the mount, motor or ESC yet, so I'm just doing some research atm. But what is the basic concept behind putting an electric motor in a nitro truck? Just put it on the tranny spur or?

I would try using the tranny locked in second (I didn't mean to say first gear sorry!) and make a motor mount out of some aluminum angle. Or email monster mike and see if he has a mount that wil work. And if you do destroy the tranny, then I'd try to find a way to use mikes universal center diff mount.--Josh

Got some pics of the GST tranny. Hopefully someone will remember a direct drive or something similar that will make this process easier:

http://i94.photobucket.com/albums/l8...n/DSC_0803.jpg

http://i94.photobucket.com/albums/l8...n/DSC_0804.jpg

http://i94.photobucket.com/albums/l8...n/DSC_0812.jpg

http://i94.photobucket.com/albums/l8...n/DSC_0816.jpg

http://i94.photobucket.com/albums/l8...n/DSC_0822.jpg

I agree, the worst that can happen is you destroy the tranny. Then use a center diff.

The pics show mechanical brakes are already set-up, so I, personally, would use them. They will save some strain on your esc with this heavy truck.

I will definitely run with Mechanical Brakes. I just need a 2.4 ghz remote with mixing capabilities then, or find another way. Not sure how to do this, but I'm taking 1 thing at a time with this. I thought I could just connect the servo together with the ESC or something in a Y harness string, and just let it go back AND forward (Like, when I hit throttle, it goes forward and does nothing, but as soon as I hit reverse, it goes backwards and brakes.)

you want a y-harness on your throttle channel: forward = forward to the esc; reverse= brakes. Just disable braking and reverse on your esc.

So, throttle servo and ESC in the Y harness to the throttle channel then?

And by the way, do you know how to grind a flat spot on the motor rotor? Or the easiest way? Thought about simply closing up the holes on the motor with lots of tape and stuff to prevent anything from entering the holes, and just do it manually. It doesn't need to be that deep.

Yes (but for you, it will be a brake servo - not a throttle servo)

Opened up the tranny today, and those metal gears look extremely solid. You guys sure these break easily?

Here's the tranny;

http://i94.photobucket.com/albums/l8...ssionsmall.jpg

From what I can understand by looking at the Revo locking guide, I have to simply remove this:

http://i94.photobucket.com/albums/l8...STGEARTHIS.jpg

And just LEAVE this be, since the centrifugal clutch is already attached to the gear, which I assume is the SECOND gear?

http://i94.photobucket.com/albums/l8...CLUTCHTHIS.jpg

Bah, been going over the gears over and over, but I can't figure out exactly how to do this. The gear that's directly on the other side of the pinions reaches down to the center diff, and if that gear was stuck to the pole I could simply remove all the others. But it isn't stuck.

The centrifugal clutch gear isn't attached to the "pole" either, and I cannot screw it or attach it to the gear next to it.

You just remove the second gear,and LOCK the centrifugal clutch in the engaged position.and then your done.I still see premature tranny destruction even being metal under a 1717,then after your tranny goes bye bye,I'd contact mike and see what he has to say or try a savage style center diff setup.--Josh

I'm going to run it with a 1527/1y 1250kv Neu motor. And btw, I can't remove any of the gears in the tranny. Atleast not the 2nd gear, it's attached to the centrifugal clutch house by bearing (The things I pointed at in the pic.)

Well,looks like you'll probably be running it until the tranny blows,or do what I would do and make a center diff mount or email mike to see if he can help you out to see if he can rework an existing mount or custom make a mount for you.--Josh

The center diff in the GST is really hard to turn around for some reason? Weird.

And, I've asked Mike for mount and center diff mount. He said he needed the car, and since I live in Norway, that's way too expensive to ship all the way to the US. I've asked some other companies though and waiting for answers.

How exactly do I use mechanical brakes on a brushless setup? Like, where do I plug in the servo? Do I use a Y harness wire, and plug both the brake servo and the ESC in there?

Starting with this question, and will get to your gearing questions soon!

You can use a y servo harness, to spilt your throttle channel to the esc and the brake servo. However the brake servo will move with the throttle and unless you have a really fast servo (like a jr9100s) you will notice a lag in braking when going from full throttle to full brake. Not a huge deal but it will take some getting used to if you currently run a brushless setup with the motor doing the braking.

I would say that having a radio that can mix the 3rd channel with the throttle channel is much better. I have run both and the mixed setup feels alot better, and gives you alot more control over the brake servo. I had mine set so it did not move when the throttle was moved in the positive direction, and only moved when I moved the throttle backwards to brake. Depending on the radio you use (I had a futaba and the guy who wrote the manual was on heavy drugs!) it may be a big pain but is worth it.

Ok, you are correct. The second pic you have an arrow pointed to the centrifugal clutch that will need to be locked to the shaft. Various ways to do with, drilling a hole in the shaft and using a hardened pin is likely the best, but it most likely works like the revo clutch does so something like what people do to lock the revo would likely work.

You also need to figure out some method of of removing the external spur gears, and replacing them with a single spur, and a slipper clutch.

I would use a new emaxx transmission input shaft, as it is long. Not sure if it is the same diameter as the input shaft on the gst tranny, hopefully it is so you can use the same bearings. This will give you the correct end to mount the revo slipper components to. Inside the tranny you will need to cut the emaxx shaft to length, and attach the small gear that works with your now locked second gear. Remove all of the reverse gears as well.

Since you are using mech brakes, go into the casle link programming, set the reverse for 0%, brakes for 0%, and the completely flatten the brake curve. You may also be able to set the MMM for forward only, but I am not sure if that option still exists.

You can also set your radio to not give any negative throttle if you plan to mix the throttle channel and 3rd channel for brakes.

Not sure if that makes sense, but that ius how I would do it. Having the gear reduction of a transmission is very important for a heavy vehicle. It will allow your motor to work in the correct rpm range.

The 1717 should work very well, I have a heavy lst running the 1717 with a MMM on 6s lipo geared for 45 and it does not get the motor or esc over 130f. Batteries stay cool as well, zippy flightmax 5000mah 40c.

Ok, thank you very much. I only need to tighten the screws in the centrifugal clutch to make it spin with the shaft, but I can't remove the first gear on the same shaft -- it's attached by bearing to the 2nd gear or something like that.

I will try to get an Emaxx input shaft, that does sound like the best option for slipper.

I ended up buying the 1527/1y (1250 kv.) neu motor btw.

1527 is a beast, what esc and lipo do you plan to run?

The 1st gear you refer to is attached to a one way bearing. You should be able to slide that gear off after you remove the 2nd gear and clutch. If you allow those 4 gears to mesh after you lock the 2nd gear clutch they will not turn.

If you cannot remove the 1st gear, do not worry, just do not instal the smaller gear that drives it when you replace the input shaft for the emaxx shaft.

http://i206.photobucket.com/albums/b...imp/tranny.jpg

I plan to use Mamba Monster with 6s lipo. Low gearing of course.

Anyhow...

Both the 2 gear on the input shaft and 2 gear on the middle shaft are locked together. The gears on the input shaft are 1 solid unit. :S

well i get to make this journey with you. i was really wanting to find a gsr, but i haven't found any rollers come up on ebay so i scored at gst roller yesturday. i really don't know which route i'm going to go for esc's i have right now are a hobbywing 12s 100a or a mgm22418. decisions decisions? i can't wait for this thing to arrive, i've never seen one of these trucks in person.

The 2 gears on the input shaft are likely one solid piece. The other two gears have to be seperate, as they rotate at different speeds. The non clutch gear is supported by a one way bearing, and the clutch hold the other gear in place. They will be removable, somehow.

They are seperate, but the first gear (On the middle shaft.) is attached to the centrifugal clutch by a one way bearing. The 2nd gear is a part of the centrifugal clutch housing - The one I pointed to in the pic you posted.

You should be able to remove the 1st gear by seperating it from the one way bearing.

do you guys know what bodies will fit these trucks? i have no real problem using a cen body, but i think i would prefer something else. i need to start gathering parts so i'm window shopping until mine arrives. thank you

Ok, thanks again linc.

How do you plan to convert it Tash?

i really have no clue until i see the truck. i've been playing with ideas with the pics i can see on the web, but i really don't know until i have it on hand. one thing i've been thinking is just trying a simple center diff setup but i really don't know the trucks gearing at this point and i may need the trans in place.

The center diff that comes with the GST is extremely hard to turn around without the transmission. It's like you can barely turn it around by hand, for some reason.

I'm going to order the e-maxx input shaft and revo slipper and just run it like that. If the tranny breaks, I'll either try to install the flux tranny in the GST or use the standard GST center diff with some sort of mounting system. Waiting to hear back from GCM.

i was thinking of maybe just making mounts and using a truggy center diff with a nice large spur, but we will see.

That's a good idea. I've been trying to get center diff mounts for awhile, but Monster Mike needed my car, waiting for a response from GCM (Going on 2-3 days since I replied with the info.), and I've asked a couple of other sites for help as well.

What about just using Mike's universal CD mount and making a simple skid plate to mount it on? That might be easier than a complete custom mount.

-JB