"Direct Drive to Diff" MT2 18SS
 

Prompted by sikeston34m's "Direct Drive to Diff E-Revo Build" thread I have started work on turning my speed demon, inrunner-powered MT2 18SS into an insane outrunner setup.

Here's what I currently have in my possession:
-HPI MT2 18SS with aluminum diff housings
-KMS 4120/6 outrunner motor
-OEMRC 100amp 12s airplane ESC with programming card
-PiStix adapter
-10 fresh A123 cells from a Dewalt 36v pack (will be run 6s normally, 10s for speed runs)
-CCBEC for running with 6s A123
-Airtronics 357 for steering, and I'll try to work with my Hitec 5245mg for braking

Need:
-turn motor shaft from 6mm to 5mm, and modify it to work for the intended setup
-Servo mounts (steering and brake)
-motor mount, looking into making one out of polycarbonate for decent shock absorbtion and low weight
-gotta make the battery packs (6s shotgun and 4s shotgun)
-work on dogbone lengths

Like the AXI sikeston34m is using, this motor uses 3 bearings, and appears to be of good overall quality. And it helps that I got it at a good discount. Also, it looks like the stator is keyed to the bearing holder/front endbell (I can take a pic of this if you guys want to see what I am referring to).

This build will be better documented than my other projects. Usually I tend to outline a project, get initial pics, finish it, and then post finished pics. But that's no fun for anybody besides myself.

Hey! :yes:

I hope you don't mind if I drop in on this thread from time to time. :lol:

I love that ESC! I wanted to use it, but I haven't figured out how to put the mechanical brakes and the servo back into mine. When the transmission was tossed out of the setup, my brake bracket went with it. I have thought about designing a bracket that bolts to the frame, since the 4120 is shorter and allows room for the brake rotor.

That's a good looking motor. Yes would you please show me the keyed stator? Sounds like a possible candidate for a custom wind project if I can make it removeable. To wind, test, take apart and rewind, test again.

Can you lead me to some pictures of the HPI MT2 18SS with the body removed? I wanna check this out. TowerHobbies shows spec but not many pictures.

4" tires.....hmmmmm. What diff ratio are we looking at?

Weight: 4.96 pounds! :surprised:

It does look like a good one to convert. I'll help you if I can.

Ok, I see it now. Diff Ratio: 2.92:1

I've been looking at the LSP and considering a Direct Drive setup for it. It already comes with the 4.3:1 Diff ratio's. I also like how the frame is setup. It comes with cvd's and alot of tough stuff. I also like how low the center of gravity is.

Same here, but I'd rather stay away from mechanical brakes if I can. I just wish this ESC could handle the braking chores of cars, but I don't think it's up to it.

No it doesn't have conventional car/truck brakes. It probably has some sort of drag brake, but that won't work.

Some good power handling ability though.

I think MGM has got it all figured out though, except for that price tag.

I agree with you 100%. I would LOVE to run the 9032, but that price tag... :oh:

This will be cool to watch come together. I will have to post my build up now, Im doing a solid axle direct drive conversion.

Here's the stator:
http://img.photobucket.com/albums/v1...d/IMG_6769.jpg

I was modifying the motor shaft, and got both ends turned down to 5mm, and the groove for the snap ring cut, using a combination of my drill press, Dremel with reinforced cutoff wheel, and file. However, I wasn't able to drill the holes the pins will go through. One hole is now about 1mm deep, but then my drill bit broke... This steel is very tough. Time to order a new drill but, and hope for better luck next time.

Better order more than just one drill bit if you plan on drilling that. Get Cobalt! That's some really hard stuff!

The AXI I used on the Revo had the snap ring too. I didn't use it. The magnetic force keeps everything in line as long as you don't have a prop out there pulling on the endbell.

That looks like one tough stator. You don't have to worry about that one spinning on the bearing holder being key like that. Thanks for the picture.

I ordered three drill bits, all having different coatings, and two of them are short-length:
-short length high-speed steel
-regular length heavy duty cobalt steel
-titanium nitride coated short length
All are about 2.5mm which is the diameter of the screw pin that holds on the dogbone cups.

Does the OEMRC 100amp 12s airplane ESC have Lipo cutoffs?

Never mind, I found the online manual and see it has the LVC built-in

Unfortunately I can't take advantage of the Lipo cutoff settings, since this truck will be running A123s. It's set to NiMh Low, so I will have to make sure I stop driving when I lose power.

What is the lowest Lipo cutoff per cell on this ESC?

I have been setting the Quark Lipo cutoff to 2.4v, I think it was, and it works great with the A123's.

By the time they get that low, they are pretty much done anyway.

MM Can do custom as well...

MM, as in my user name or Mamba Max? LOL
If you're referring to the Mamba Max, that's true, but it doesn't pertain to this discussion. If you're referring to me, then I'm just confused :lol:.

The OEMRC 12s 100amp ESC can be set to cut off at 2.6v, 2.85v, or 3.1v. 2.6v is a bit high for A123 IMO, which is why I have chosen to run the truck until it dumps.

I checked the Quark Manual. It was 2.2v per cell that I was setting the cutout at.

They are pretty much done at 2.2v, but yeah at 2.6v, they still have some left. :yes:

I'm curious as to how smooth the OEMRC 12s 100amp ESC is and how well it works with the pistix adapter.

Have you tried this ESC yet?

Nope, I've only programmed the ESC so far (which is very simple and fast with the programming card). It will be direct soldered to the motor, and since the motor's apart (waiting to have holes drilled in the output shaft), I haven't soldered them together yet.

So I've made some progress... But not much. I received my order from McMaster-Carr containing the 3 drill bits. After trying all 3, I was able to determine that this shaft is very hard.

But in all seriousness, the steel used is harder than any other steel I have worked with. The 2.5mm carbide drill bit wasn't able to make any progress on it. I have an older 1/8" (3.17mm) carbide-coated drill bit that was able to penetrate, but it is of course a larger diameter than what it should be. All of this was after setting up my cross-slide vice on my drill press table, and setting it all up perfectly and tightening everything up. The use of oil made no difference.

(jeez, I don't think I have made so many sexual references in one post)

On to the pics:
http://img.photobucket.com/albums/v1...d/IMG_6776.jpg
http://img.photobucket.com/albums/v1...d/IMG_6782.jpg
http://img.photobucket.com/albums/v1...d/IMG_6787.jpg
http://img.photobucket.com/albums/v1...d/IMG_6788.jpg

And I also made a vid of the motor running:
http://video.google.com/videoplay?do...27213169795459
The black disk I put on is the brake rotor.

Cool - I look forward to seeing it in person.

Yes, I got a strange reaction when I told my GF that I was having trouble working with this hardened shaft! :lol:

That stuff is like bullet proof. There is another way to do it, if you have a cutting torch. You can heat it up Cherry Red, then let it cool off VERY slowly. This removes the temper from the steel. Then it's alot more workable.

To restore the temper and regain the hardness in the shaft, (this is an age old question that just recently got answered! :lol:), You heat it back up Cherry Red again. Then you Quench it quickly. I was told to be VERY Careful, because there is a pretty violent reaction, especially if you use water. I was told quenching in Oil works better. If you want to hit the middle of the hardness scale with your shaft, (:lol:), you heat it up until it just turns a little brown, then quench it.

Well since I was getting this information from my local machine shop, I just opted to order some 6mm shaft material that was of a slighty lesser hardness. Then I made my own custom shafts from that. It worked great.

You might take a look at the E maxx output shaft to the transmission. It is 6mm in diameter and already has the "hoe" in it for the cups. LOL Just see if the length is compatible with what you need.

Dremel makes a small diamond tipped cutter that will cut the stuff. But it's still a challenge at best.

Hmmm, I wonder if the CVD cups and shaft for an E maxx would work?

That's the sound of an outrunner alright. I think they are very cool. Very Quiet also.

Nice pictures. I like that ESC alot. Can't wait to hear about it's performance in a land vehicle.

For some reason the digital camera didn't really pick up the sound of the outrunner very well. At higher RPMs it sounds like a futuristic ray gun or something (it doesn't sound like that in person).

Only problem with the E-Maxx output shaft is that it's 6mm at the ends (like the Revo is), but the MT2 uses 5mm outputs. Also, I think the E-Maxx output shaft would be too long to fit on the chassis. Good idea though!

Sometime I might try that dehardening and rehardening method (with the steel shaft, of course :lol: ). But for now the holes are deep enough that there are set screws sitting in them, and it's a very solid fit.

Emaxx is 6mm. Tmaxx tranny ouput is 5mm. I just used a tmaxx and emaxx driveshaft on mine, worked like a charm. If it is too long just cut it down.

We're talking about the output shaft from the transmissions. Without the holes through the outrunner's shaft, I couldn't use the T-Maxx tranny outputs anyways.

Use a medium to removeable strength locktight for final assembly. I put some in the hole before I put the set screw in. The low viscosity Green Medium Strength by Permatex is my top choice for this. The set screws will still break loose with an Allen Wrench, plus it wicks into the space between the endbell and the shaft. This helps strengthen things. Also use it or Blue removeable on the endbell set screws. It would be a really BAD thing for the endbell to come loose from the shaft.

The E maxx output shaft is 67.6mm long. It is 6mm in diameter. If this length is compatible, it's much easier to turn the hard stuff down to 5mm for the drive cup fit, than it is to drill a hole in it. Just put it in a drill press, spin it, and use a file on it or even a Dremel tool. But if you are satisfied with yours already, then it's all good. The set screws should hold just fine with some loctite.

Hey JohnRob, You gonna make a thread on your build? I would love to see some pictures.

My E Revo is currently waiting on more upgrade parts.

1. 125amp Quark Monster Pro - I will do a small Cap mod to it, mount it with some thermal compound to the Aluminum ESC mount, then I intend to eliminate the 4mm connectors and the extra wire length. I'm going to go right down through the top of the ESC mount to the motor. About 2 inches of wire is all there will be from Motor to ESC, Once I settle on the final motor that is.

2. Castle Creations 10amp BEC. I'm going to make this a permanent fixture for this setup irregardless of what Battery setup I'm running. It's more efficient and takes that much heat further away from the ESC.

3. Custom wound 4130 - I'm still waiting on my 22Ga. 392 degree winding wire to get here.

I wanna crank this thing up. :yes: I'll make some more Video's too.

Blue medium strength is what I use on everything. It's already on the set screws holding the shaft, and on the set screws holding the cups to the shaft (and on the end of those set screws).

The E-Maxx output shaft, if 67.6mm long, is actually just about the perfect length for the motor. However, it's got that big chunk of metal in the middle, which would take a while to turn down or cut off.

That big chunk comes off pretty quick if you put it in a cordless drill, then hold it against a Bench Grinder. I take my time and don't get it too hot. Just stopping occasionally to cool it with cold water. Get it down close, then use a file on it to rough cut some more, and final polishing is done with sandpaper.

You might be surprised how fast this little procedure is. I removed the center "chunks" from two of the Revo Output shafts, fully prepped in about 30 to 45 minutes or so.

Fascinating thread thanks all.
I love that outrunner video- BIZARRE to see the can spinning!
Regards
David / ICUBoy

Good to know, I might do that in the future.

I have some good news - the motor mount is almost finished, and is made out of 1/4" polycarbonate, that was bent to 90* with a heat gun. The brake assembly is finished, and should work adequately. Now I just need to figure out battery mounting, chassis bracing, steering servo mounting, and ESC mounting (this ESC is HUGE). I just wish the MT2 chassis weren't so small.

Let me know how the Polycarbonate Motor mount works out. I feel like I could have saved some weight with the use of other lightweight materials such as Carbon Fiber.

One desireable trait about Aluminum is it's heat sinking ability. :yes:

I have aluminum angle that would have work just as well as a motor mount, but the polycarbonate is flexible, which will hopefully keep the motor in better shape in case of a crash or whatever (considering the force acting on the motor when it's spinning). That's sort of a problem, because the end of the motor can hit the bottom of the mount when the mount flexes. I think I will brace it, but we'll see.

I want to see some pics!

Im curious to see how you do your motor mount

Unfortunately you'll have to wait a couple hours, when I get home from school. But in case you want a visual, the motor mount is a 1 1/2" wide x 4" long x 1/4" thick piece of polycarbonate (clear) bent to a 90 deg. angle, and the bottom leg sits below the motor.

Thats fine =)

Thanks

Woops, it's been a couple days... But the truck is now "finished" (with quotes because we are never actually done with them).

The servo mount is made from T-Maxx throttle servo mounts that were put in a vice to be narrowed with the help of a heat gun, were then cut down to let the servo sit lower, and were drilled.
http://img.photobucket.com/albums/v1...d/IMG_6798.jpg

Motor mount is 1/4" thick polycarbonate bent to a 90 deg. angle with a heat gun, and drilled to accept the motor and the screws to hold it to the chassis:
http://img.photobucket.com/albums/v1...d/IMG_6813.jpg

The brake setup uses the pads/rotor from the MT2, and an (obviously) custom actuator bar bent from steel music wire, that is held to the chassis with screws :lol:. The mini brake servo is a Hitec 5245mg that was left over from when I put in a standard size servo onto the chassis for my CRT.5. That servo is simply servo-taped to the chassis.
http://img.photobucket.com/albums/v1...d/IMG_6803.jpg
http://img.photobucket.com/albums/v1...d/IMG_6809.jpg

The brakes are decently strong, certainly nothing too impressive, though

Next up was ESC mounting. Quite a pain, considering the size...
http://img.photobucket.com/albums/v1...d/IMG_6819.jpg

But I figured it out, and managed to incorporate the ESC mount into a brace for the motor mount, that will keep the mount from flexing (from the weight of the motor), where the flex could cause the spinning can of the motor to hit the motor mount. The brace/ESC mount mounts to the motor mount by 4 screws, and 3 screws hold the ESC to it.
http://img.photobucket.com/albums/v1...d/IMG_6829.jpg

Then I had to figure out a battery solution. I had a virgin Dewalt 36V pack that was out of the casing. I knew I wanted a shotgun-style pack (like the NiMh stick packs) because that's what would fit on the chassis. What I did was simply bend the tabs that were already between the cells, to give me a VERY simple 6s1p pack, that took all of maybe 10mins to make, with the only soldering being to attach wires and a Deans connector to it. It is secured to the chassis with industrial strength Velcro along the whole underside of the battery.
http://img.photobucket.com/albums/v1...d/IMG_6832.jpg

With the 4 remaining cells I plan on making the same style of pack, but shorter. The result will be 10s1p A123... Can you say POWER?

And here's another overall view:
http://img.photobucket.com/albums/v1...d/IMG_6827.jpg

You can see the custom rear brace, and there's a similar brace in the front that's kinda hidden, that attaches the front upper deck to the chassis plate.

Nice!

Really tight for room, lol I like your breaks:party::lol:

Have you ran it?

Today I maidened the truck. Initial thoughts were, "wow, this truck takes off fast". The minimum throttle position results in a pretty high speed, but that's not surprising considering the cheap airplane ESC and the direct-drive setup.

As others have found, outrunner startup is odd. If I GRAB full throttle, there will most likely be harsh cogging (and some interesting musical tones). If I grab some throttle, the truck might move a foot smoothly, and then encounter some cogging, only to take off. It doesn't happen all the time, especially more recently since I'm learning how the throttle wants to be worked, but when I do get past this "post first-foot-cogging" point the truck accelerates like no other... Too fast, in fact. Traction becomes a HUGE issue with acceleration like that.

After work I pushed the truck pretty hard on asphault with the tires shown (worn down HPI Dirt Bonz). The motor and ESC had no problems taking the abuse. Only problem I noticed, is that the ESC has a bit of a lag to it when getting the motor RPM up to the point it should be at relative to the trigger position. That is really only an issue when I'm trying to do drifting (be it on asphault or a waxed floor).

Unfortunately the truck doesn't seem to like this much power. Previously with a Feigao 9L and 4s2p A123 it had problems with the diffs clicking (with the hardened diffs), yet inside the diff housings there was nothing but a little grease. That's when I went to aluminum diff housings. During the pavement run, the rear diff actually went out, and since a new ring/pinion costs $32, I'm hoping it's just the internal diff gears.

I wonder if there is a speedo that wont cogg..... cogging REALLY bugs me, but I would like to do a direct drive car, its not near the top, but would def be a fun project

Sounds like she runs good though... Whens the vid? =P

TBH, I think you're gonna have to wait a while, for us to figure out what the solution is to this cogging (and it looks like sikeston34m and John Holmes are working on this with custom wound motors). But for me at least, this cheap airplane ESC has to be contributing rather significantly to the cogging.

Uhhhh.... I guess it will have to wait for the rain to stop.

Yeah, I have no clue what I would do direct to diff in... but that will be cool when the cogging is gone, or close to gone

Darn rain!

Nice looking conversion Metalman! You were right, the MT2 chassis is quite a bit narrower than the old redcat that I am using. You still managed to get everything in there, and I really like your mech brake setup, quite innovative!

I am suprised that the esc is having problems, what kinds of adjustment does it offer? If it has some sort of startup power or torque adjustment, set it to high, or full. Since you are using mechanical brakes and high voltage you could try a phoenix 45 hv esc. The castle startup should be better.