Direct Drive to Diff E Revo Build - Page 6 - RC-Monster Forums

sikeston34m · 11.16.2007, 02:37 PM

With using Aluminum for the motor mount and the ESC mount. The whole thing is acting like a heat sink, even to the chassis.

I really think it's going to take some major voltage before heat becomes an issue.

Mod Man · 11.16.2007, 05:47 PM

Going up in voltage may cure the cogging too. I had that issue a while back. I almost bought a different ESC untill I tried higher voltage. :)

Looks good!

Matt

suicideneil · 11.16.2007, 05:57 PM

That thing is gonna really confuse a lot of people when they see it for the first time- no visable motor!

zeropointbug · 11.16.2007, 06:38 PM

Can anyone say "perfect left-right balance"... if you lower this thing for stance a bit, it would murder at a race!

sikeston34m · 11.16.2007, 06:43 PM

Quote:

Originally Posted by BrianG

Isn't there some kind of rule-of-thumb that states the motor has to spin a certain minimum percentage of its kv rating for the ESC to get the proper back-EMF pulses? Don't know if the same rules apply to outrunners, but it may be something to think about as far as cogging is concerned.

And HOLY COW that's a big motor! You plan to sit on your vehicle while you drive it?

Very good Point you brought out there Brian. I'm not sure what that equation is, but I think I'm over the line on the cogging side with this setup.

I just tried the 6S2P setup with a receiver pack. Cogging on startup is still there. It's not horrible to the point where it won't move. I just can't stab the throttle and explode off the line. Top End is alot faster on the 6S A123 setup with NO heat issues at all. Barely felt anything from the motor or ESC, even after top speed runs.

I tried the ESC in outrunner mode and inrunner mode. Inrunner mode works best. I adjusted the throttle trim on the controller, and it would then let me into advanced programming.

This is geared too high. I thought the AXI 4130 would make up the difference in torque to compensate for gearing, but it doesn't. I'm not getting the kind of acceleration I'm looking for.

In my mind, I am constantly comparing everything to the E maxx Direct drive to transmission setup. With it, I used up to 800kv outrunners. On the E maxx, Input shaft to Tire is a 4.57:1 gear ratio for 2nd gear. I will be ordering the 4.3:1 RCM Revo Hybrid diffs for this. This will almost duplicate the gearing of the E maxx and further multiply the torque to the wheels. All without a transmission and those wear items that tend to be weak and break.

I could see some GREAT results from the AXI 4130 with the lower gears IF I could put it on 10S Lipo. But for now, to stay within the voltage limitations of the Quark, I'm thinking about going with a different AXI motor.

The E maxx outrunner's stator is 35mm in diameter with a length of 20mm and has a kv rating of 650. The AXI 4120/14 has a stator the is 41mm in diameter (torque bonus) and is 20mm long with a kv rating of 660. The cooling fan attached to the back of the motor works with the 4120 also.

The 4120/14 is rated for 4 to 5 Series Lipo, but in this new setup, motor temps will determine how much voltage it can be fed. I think this setup dissapates heat very well, so 6 Series Lipo is possible.

Without batteries, the truck in it's current state weighs 9 pounds 8 ounces.

sikeston34m · 11.16.2007, 06:46 PM

Quote:

Originally Posted by zeropointbug

Can anyone say "perfect left-right balance"... if you lower this thing for stance a bit, it would murder at a race!

One thing I noticed during the 3 runs I've done today, The motor being so low acts like a balast weight. I did some high speed turns and I didn't flip this truck once today. I'm very pleased with the center of gravity.

sikeston34m · 11.16.2007, 06:59 PM

Oh No! The RCM Hybrid Diff's are out of stock!

I tried emailing about ETA but the mail bounced back because the mailbox is full.

I wonder when they will get them again?

ib4200 · 11.16.2007, 07:01 PM

Quote:

Originally Posted by suicideneil

That thing is gonna really confuse a lot of people when they see it for the first time- no visable motor!

lol yeah you should try to cover up the motor as much as possible

zeropointbug · 11.16.2007, 07:22 PM

Does the setup have enough torque to wheelies at speed? What Kv. is your motor?

So you are talking stator dimensions, not the outside dimensions, correct?

One of those Scorpions looks larger than the Axi, 40mm stator, 25mm length.

I don't know what rpm the motor is hitting, but I know an outrunner should be hitting 6500-7000rpm to get 45mph in a Revo with moderate ballooning tires.

sikeston34m · 11.16.2007, 07:43 PM

Quote:

Originally Posted by zeropointbug

Does the setup have enough torque to wheelies at speed? What Kv. is your motor?

So you are talking stator dimensions, not the outside dimensions, correct?

One of those Scorpions looks larger than the Axi, 40mm stator, 25mm length.

I don't know what rpm the motor is hitting, but I know an outrunner should be hitting 6500-7000rpm to get 45mph in a Revo with moderate ballooning tires.

No it will not wheelie. The AXI 4130/20 is 305kv. It's the largest motor that produces the most torque that will fit the space and the stock transmission output shaft.

Yes I'm talking stator dimensions.

On 6S A123, I figure I'm hitting about 5500 rpms.

zeropointbug · 11.16.2007, 09:12 PM

Okay, well how much does the motor weight?

I find that odd that it is not doing wheelies with that large motor... I think this outrunner business is going to be a little tricky at 'sorting' out what works and what doesn't.

sikeston34m · 11.16.2007, 09:37 PM

The AXI 4130/20 weighs 14.4 ounces. The 4120/14 weighs 10.9 ounces.

It is tricky sorting out what works and what doesn't.

I can't wait for the new E maxx to come out. I have that outrunner setup pretty much perfected all the way to the point of blowing the transmission. The new Tranny is 2 1/2 times tougher? We'll see about that.

The Quark does well with the E maxx outrunner setup, but I think the cogging in this setup has to do with what Brian said. There isn't enough EMF back pulses at low rpm because of the high gearing.

At 2.85:1 gearing, the truck moves about 6.5 inches for each rotation of the motor. Wow! I just did the math on that. That's quite a load actually.

At 4.3:1, this drops to a little over 4 inches. Big Difference. Hmmmmm.......

There's definately a sweet spot to this stuff. I could change the tire size, but I really don't want to do that. It's a Monster Truck! LOL

I'm not giving up on this, but where can I get some of the Hybrid Truggy diffs? Even just the cases, I'll come up with some gears.

ib4200 · 11.16.2007, 10:48 PM

just as an experiment run it on rwd to see if the less resistance makes it go a little faster

zeropointbug · 11.17.2007, 01:28 AM

you would only gain maybe 1mph? maybe ♠2?

sikeston34m · 11.17.2007, 11:29 AM

OK on to the next phase of this project. Hybrid Diffs. I can get the cases, but I have to come up with the gears.

The Hotbodies gears are compatible with the RCM Hybrid cases. In searching for parts, I found this http://www3.towerhobbies.com/cgi-bin...?&I=LXLGX2&P=7

It appears to have a 50 tooth spiral ring. Would this be compatible with the 10 tooth pinion? Here: http://www3.towerhobbies.com/cgi-bin...?&I=LXJBM3&P=7

This combination would give me 5:1 diff gear ratio which is even better IMO than the 4.3:1

With the Emaxx, from input shaft to tire the ratio's are:
1st gear: 5.62:1
2nd gear: 4.57:1

5:1 is perfect! Power it with a AXI 4120/14 at 660kv and watch it fly!

It seems there is another issue with the Hotbodies pinion. Here we have a 8mm shaft with no hole? What's the answer to this?

Maybe this? http://www3.towerhobbies.com/cgi-bin...?&I=LXFWS2&P=7

I could turn the cvd's around backwards and put the dogbone end at the diff. Are the two compatible though?

Hmmmmm.........I wonder.