Direct Drive to Diff E Revo Build

[johnrobholmes]

I am totally in love with the concept. Who needs a stinkin gearbox when you have people like Sike? The weight savings would be HUGE! (rummages for 3032 outrunner)

[DrKnow65]

Weight down low, no gearbox to fail, efficient, and soooo slick. What's not to love about it? (mabey the high voltage is a little pricy but you do get what you pay for) did I mention efficient and less stuff to break?

[lincpimp]

I guess that I should do some mods to the old direct-to-diff redcat and see what it can do. Need to find a lower kv motor, most likely a 600-650 would do. That will allow me to put some taller tires on it and it will be more off-rad capable.

The main benefit I found was that there was so muck more room on the flat chassis with out the center diff/trans there. Batteries could be placed on either side of the chassis and the balance was great.

Any ideas on a good out runner with 600-650 kv that would run 5s well and have a 5mm shaft? Here is the info on the motor I am currently using, would like to keep the same diameter if possible:

Specifications:
-Rpm(Kv): 833Rpm/V
-Continuous Currect: 50A
-Max Currect: 70A
-Watt: 980W
-Max Eff: 98%
-Recommended Rotor Prop: 8 x 4 to 15 x 8
-Weight: 150g ( Motor Net Weight )
-Total Length: 78.2mm (include Front and Black Shaft)
-Motor Body Diameter: 37.1mm
-Shaft Diameter: 4.98mm(Front and Back)
-Shaft Length: 15.1mm (Front) and 14.2mm (Back)
-Recommended Input Voltage: 8 - 23 Volt

[johnrobholmes]

looks like the dimensions of a 28mm stator motor. 980W for a 6ish ounce outrunner? Certainly not constant, and the efficiency looks fishy too.

A 3026 would be close http://www.innov8tivedesigns.com/pro...products_id=80 and you could do a custom wind.

[JERRY2KONE]

The good thing about trend setters is that they lead the way for others, which in turn creates a market for the parts involved in a conversion poject like this one. So hupefully within a reasonable amount of time this can bring the price of this conversion down. Then more of us can afford to bring our trucks to the same level without breaking the bank for a hobby truck. Creating a group of vehicles that can race at that same level with less weight, less broken drivetrain parts, and increased efficiency, not to mention a much cleaner experience all around and less frustration unlike Nitro. Way to go Sike for going all the way with this project.

It kind of reminds me of the aspects of the NASCAR organization which sets things up so that having vehicles that are vitually identical creates the situation which means that winning any race is soley in the hands of the driver and his crew (the human factor). This has the looks of a very sucessful build Sike. Thank you for sharing it with all of us and keep up the good work. I for one look forward to the completion of this one so we can all learn from your work.

[DrKnow65]

Yah, a $70 motor that's 90% efficient is a real good place to start.

I've got a thread about CF parts open now, I'd love to see a bolt in chassis that has integraded battery trays, motor mounts (mabey a motor that runs well on 6S when the MMM finally shows up) all the misc. bit and pieces and the diffs in a kit to make the ultimate e-Revo conversion.

I would spend money on that, and I think the guy's that see it would too. Especially the guys that are dealing with the nitro dissapointment and already own the revo.

[MetalMan]

This "Direct Drive to Diff" method definitely has plenty of advantages. But to keep everything in perspective, there are also disadvantages:

-harder on diffs, due to lack of torque control (slipper clutch) or a way of transferring power (center diff). But since the vehicle should be lighter this way, that means less mass to move.
-battery placement - I like to run a single pack on the opposite side of the chassis from the motor. However, unless you have a Losi 8 or 8t, the motor will need to pretty well centered, which can disrupt battery mounting on narrow truggy/buggy style chassis.

For my MT2, the chassis is way too narrow for the diameter of my motor to run a battery on each side of the chassis, along with the servo up front on one of the sides. So, I'm gonna offset the motor to the left, and stand the steering servo up (on the left). That way I have maximum space on the right for battery mounting. There will also be the brake servo and maybe the ESC at the left rear, behind the motor.

[DrKnow65]

I considered the clutch idea, I may have to look a little better into that. Was thinking for cogging issues (if one were not to mod the diffs) but I could see where having it for drivetrain insurance is smart too.

[MetalMan]

I think a clutch between the motor and each diff (two clutches total) would work.
The idea I have come up with is more or less a ball differential with no gear and one of the outdrives will be replaced by a part that mounts to the outrunner's shaft. One problem I can see is getting this slipper clutch-thingy able to handle that much torque - normal slipper clutches spin at higher RPMs so the torque is less, but here, the RPMs are lower so the torque is greater.

Then, a one-way could even be used after the front slipper clutch to give us rear-wheel braking only, allowing us to pitch the rear end in turns.

Also, it turns out that the shaft that came on my motor will work to mount the dogbone cups to with only slight modifications! And the 6mm shaft I have is about 0.0015in. larger in diameter than the shaft that came on the motor (doesn't fit).

[sikeston34m]

I put the E maxx Tires on with 4S Lipo. Here's a taste of what it's doing.





Second vid looks scrunched. I think the aspect ratio got changed somehow.

I think I need to shim the rear diff, pinion to ring. I believe I heard it pop a few times. It sounds like the pinion is skipping a tooth when I jump and land.

What shims do I use?

I think the aluminum diff cup is a good idea also. The plastic one must be flexing and allowing this to happen.

Bullet Proof Diffs are a must. I won't run it on 6S until I get this fixed.

Overall, it seems to be working very well.

[aqwut]

cool vid... I really like the sound it makes... it's so quiet...

[JERRY2KONE]

it is so quiet that it almost makes you want to put a sound system in it that makes the sound of a nice muscle care to match the awsome power that it has. Maybe a Shelby Msutang GT, or a Dodge Viper RS. That really is a cool setup though Sike. Where to go from there?? That is the question??

[sikeston34m]

@Metalman:

Please share your ideas if you come up with something concrete on the shaft/slipper thingie. I believe in a Monster Truck, a clutch assembly ONLY on the rear shaft would give you the results that you're pondering.

The rear diff is the one that takes most of the abuse. This would retain full braking power with the front diff.

On the shaft material that you have, cut it to the length you need, stick it in a drill press, then sand it down with the chuck spinning at a good speed. Do a little at a time and check it. You might be surprised at how well this cuts. I always used a motor bearing to check the diameter as I went.

This type of setup is hard on the diffs. That's why I've went to the lengths that I have to insure diff toughness. I think if a diff is tough enough, it should be able to withstand jumps with full throttle landings. Or at least, I think that should be the goal.

I ordered the Aluminum cups for the diffs a few minutes ago. A little extra insurance against internal flexing.

I also took out the rear diff and redone the shimming. I wanted to tighten it up, so instead of 3 (.2mm) shims behind the pinion, I now have 4 there. I also put one between the ring gear and the bearing to move it over just a tad.

When I put the diff back together, it spins freely with no pinion play at all. There was some play before.

[sikeston34m]

Originally Posted by JERRY2KONE

it is so quiet that it almost makes you want to put a sound system in it that makes the sound of a nice muscle care to match the awsome power that it has. Maybe a Shelby Msutang GT, or a Dodge Viper RS. That really is a cool setup though Sike. Where to go from there?? That is the question??

Where to from here? The only way to go is UP.

Up in voltage. I'm going to be playing around with this setup for awhile before I get the money for a HV ESC. I want to try it on the 4S A123 setup. I really like the A123's.

I also feel more confident now about the diffs, so we can proceed.

HV ESC choices that I'm considering are either the Jazz or the MGM.

The truck will get really crazy on HV. On HV, I might decide to go back to the 4130/20. It will have more torque than the 4120 does and get all kinds of crazy since HV will spin it up very well.

[johnrobholmes]

Glad to see how well this turned out with the proper rollout. I picked up a 4ft section of L channel today. Time for more "research" into this. Got any taller tires you could throw on your rig to test a higher rollout ratio?


Maybe I missed it, but what ESC did you use in the vid? Sounded like a quark to me.