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Mt2/Crt.5
It was only after I sold my MT2 and paid 3 times as much for a CRT.5 that I realized just how similar they are. It seems like the CRT would be better if it was a little longer and guess what, the MT2 is. I bought the MT2 because I had blown up the diffs on several 1/10 cars with BL. I thought the MT2 diffs probably would hold up. I moved on to my E-Maxx without doing the conversion. The CRT is more refined and the center diff makes it much more driveable. So now I wonder how I could incorporate a center diff into a direct drive build. It might also provide the key to reducing driveline shock?
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The HV-45 would be nice, and would definitely start better (my HV-110 starts the KB45 in my Savage very nicely), but it's still $35 more than this OEM RC ESC. Quote:
It would be interesting to incorporate a center diff into an outrunner motor. Based on how we are currently doing this "direct drive to diff" stuff, there doesn't seem to be a way. However, a oneway on the front driveshaft would be helpful, as it would allow us to have rear-only braking, which can put the trucks sideways into turns. There has also been another way to reduce stress on the driveline that we have only briefly discussed - adding two slipper clutch setups, with each one between the outrunner motor and the diffs. I've put some thought into it, but am very far from actually making anything of that type. |
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You did a great job. It does sound like you got yourself a good taste of outrunner power. I didn't know there was such a thing as too fast? :intello: Outrunner's do have a different feel to them, but the acceleration can be blistering. The power to weight ratio of the outrunner motors are pretty impressive IMO. They definately make for numerous new possibilities. Bullet proof diffs are a must, especially the rear one. This is why I chose the Revo, knowing that Mike could set me up with some REALLY tough diffs. When you get your diff replaced/rebuilt, try playing with the timing some. Timing can really make a difference. |
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Be thinking ahead of time about upgrading your diffs. The rear one won't last long. |
MetalMan, that is a really cool project. Thanks for sharing the build. Is there a smaller outrunner motor that would work good with a MambaMax and fit in a CRT.5? I really like my CRT.5, but I wish it was lighter and had more room on the chassis for batts. Does removing the center diff make driving on a track a lot harder? Is the direct drive system more for bashing?
Thanks again! |
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I honestly couldn't say if this setup is good for bashing. Bashing can put a lot of strain on drivetrain parts as it is, and if you remove the center diff and not have a slipper clutch with an outrunner setup, you'll put even more strain on the drivetrain components. As for driving with this setup on a track compared to a center diff, I have absolutely no idea. We can make guesses, but no one has tried a "direct drive to diff" outrunner setup on the track so far, and certainly no one has compared it to an inrunner/center diff setup. Well, I have good news. I took apart the MT2 diffs and found no metal shavings in either the diff housing or the diff cup. There was, however, a wheel nut that loosened while driving last night, which caused one of the wheel to get stripped at the hex (the MT2 has metal drive hexes). That was the problem that I thought was the rear diff. |
I'm glad you found it wasn't any worse than that. :yes:
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Just did some experimenting. Earlier I made the 4s pack, so now I have 4s, 6s, and 10s to use. But since one of the other wheels was stripped, I had to switch to some Road Rages, which are half an inch smaller in diameter than what I was using yesterday.
First was 4s on the original settings (highest start power, high timing). This was actually decent, fast enough to not be slow, and totally controllable. Only downside, this ESC doesn't like to react quickly to throttle positions below half throttle. Then 4s with low timing. This had less cogging, but it seemed the motor didn't like it as much. 6s and low timing, I found a weird thing that I can make happen - if I'm at 1/4 throttle and grab WOT the truck makes the strangest sound I've ever heard from BL. It sounds like the motor is screaming! And it's not very high pitched, I guess it's sort of like a crow screaming. 6s and medium timing, this "crow screaming" was reduced, and cogging wasn't too bad. 4s and medium timing didn't result in the screaming crow, and there wasn't really any cogging. Next, 10s with medium timing, and I had to use a receiver pack since the CCBEC can only take up to 6s Lipo. This made the truck EXPLOSIVE. Traction was a HUGE issue, and I don't think I exceeded 3/4 throttle on my street. I need a bigger space to open it up on 10s. |
I really think that the direct to diff outrunner setup could do with some sort of slipper arrangement. I was thinking to use a revo slipper on each end of the motor. Where the spur is normally mounted, a plate with standoffs and some sort of adapter to mount a drive cup could be substituted. This would require shorted center driveshafts. Not sure if this would be feasible, but it is all I can come up with.
Here is an idea that will really annoy the electric diehards!!! Why not make the center shaft of the outrunner capable of mounting a nitro clutch on either end? That would create a mechanical disconnet, and cure the startup cogging problem. Mechanical brakes would also have to be employed though, raising the complexity a notch. Plus I have no idea how big the diameter the nose of a nito engine crank is. It would have to be smaller than 5mm to allow the shaft to plass thru the bearing, etc, in the outrunner. Bigger outrunners use the 6mm shaft, so maybe it would work. I only throw this idea out cause the cluch adapter on my revo really makes the motor work smoothly. I have no idea if the nitro cluch would be strong enough to handle the power and torque of the outrunner. |
Hey Linc,
The clutch is an idea if you can come up with the mechanical aspects of it. Design I mean. It's a tradeoff since you have to use mechanical brakes though. Just remember, down on the center driveshaft there is MUCH higher torque and higher gearing. Hey Metalman, LOL@Crow screaming. That's gotta be strange. I've never tried an outrunner on 10S A123. I have tried an E maxx Outrunner setup on 6S2P A123 which resulted in stripping the hole in the tranny drive dog. I wasn't jumping or anything. It was from HARD acceleration with a 715kv 3530 5 turn. Sounds like High Timing works good on that setup. Can you get us a video of this thing? :yes: |
Video is gonna have to wait. My friend who is also my cameraman works tomorrow, and after that I will be busy with finals.
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Clutch
I've been thinking of something like that too. Just needs a little free spin to get started. You could run some very high gearing (or kv) with the right kind of slipper. One on each end I guess. I've always thought that mechanical brakes were a good idea anyway.
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Too Fast
Yes, there is such a thing. A RC car/truck is too fast when it creates more lift than it has downforce.
For the MT2, that point seems to be reached at ~65mph (guess). I was doing 10s1p runs with the body on, and the warmer weather/hotter asphault compared to last night helped a lot with keeping the truck more stable. Fewer cars on my street also helped. I was increasing speed with each pass, to get the feel of how the throttle should be worked. Then one pass, the truck lifted off! And it wasn't due to a blip of the throttle, or an imperfection of the pavement, because the back end lifted off. I'd say the truck got a good two feet into the air before coming back down to the ground, and tumbling. The only noticeable damage was a broken rear ball end and a ripped from bumper. And of course both the 10s pack and the receiver pack were ejectected, despite the good strength of the industrial strength Velcro. Now I need to work on downforce... |
If you want a really high down force body, try out the lola style bodies from proline. The 1/8 scale size would most likely work on your truck, and cover up the wheels for better aerodynamics.
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That is a good idea, but I still want it to look like a truck, 'cuz otherwise I would've gotten an onroad car :angel:.
I just ordered a wing mount and wing mount adapter from New Era Models that will let me put an 1/8 wing on the back. Should help a lot. Once that gets here, I will see if anything needs to be done to the front of the truck in terms of downforce. |
Sounds good, I like the truck look myself. i have a few 10th on road cars and use a lola body for my top spped runs. The body will completely compress the shocks at 70+ mph!
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Better tell that Motor it's in a truck, Not an Airplane! |
You could call it Chitty-chitty bang bang....
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Downforce on this truck was never worked out... I gave up and went to 5s2p A123 and a MM/CCBEC, and ditched the mechanical brake. This setup ran well except the center-front Jato driveshaft couldn't stay on the motor shaft since it lacked the proper screw pin to secure it (just a simple set screw). Basically I'm giving up on the MT2, but its front end is going toward my Corr truck project and its other components will be useful elsewhere. This will also help create some new space 'cuz quite frankly I've run out. A 4wd 1/10 truck won't be missed, though, as I still have my CRT.5.
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