Electronic center "diff" Revo Conversion - RC-Monster Forums

MetalMan · **Electronic center "diff" Revo Conversion -** 02.05.2008, 11:58 AM

An idea I've been fond of for some time now has been to implement multiple BL motors into a RC vehicle in order to gain increased control over the rotation of the tires. One thought I've had is an on-road car which uses one motor per tire, and by controlling each motor individually through a radio (like using "Tank Mode" on my Nomadio React) I could basically make 3 electronic diffs. One "diff" up front, one in the center, and one in the rear. The front and rear ones would help with turning and traction control (with the help of a gyro or gyros), and the center "diff" would control front/rear acceleration rates as well as brake bias (like a center diff + mech. brakes).

But since I don't have the time or funds to develop an on-road car with 4 motors, 4 ESCs, and a specially designed chassis, I'm thinking of trying this electronic "diff" idea on my (currently) nitro Revo 3.3.

With two outrunners of appropriate size and kv in the middle, each with a driveshaft attached to it, and two CAR ESCs, I am quite confident I can accomplish this.

Here's my plan:
-two Sidewinder ESCs with power inputs hooked in parallel (so they draw from the same source), hopefully they can take 5s A123
-two 4110 to 4120 outrunners of about 500 kv
-5s2p A123 (I've already got two of these packs)
-Nomadio React (already have this, and it is capable of quite advanced channel setup, even better than channel mixing)

The front MM would have a lower brake strength, as well as less punch control than the rear MM. This will allow the front to pull better under acceleration, but also give the rear stronger braking to help the rear slide out a bit.

Because of the advanced channel configuration of the React, I would be able to alter things like exponential and endpoints of the front and rear independently from each other, on the fly, to fine-tune the driving without touching the ESC settings.

The key here really is the radio: As I've said countless times before, I really love the Nomadio React

.

Opinions, criticism, anything will do. I've got to save up some cash before I can attempt this, so things can change.

jhautz · 02.05.2008, 01:34 PM

The first question I would have is that the ESC controlling the rear wheels would for sure see higher acceleration loads than the front. In heavy acceleration I would think that almost all of the load would be on the rear esc. Not sure if a sidewinder would take that.

Sounds like a cool experiment anyway. Looking forward to seeing this thread develop

MetalMan · 02.05.2008, 01:42 PM

I could always swap out the rear Sidewinder for a MM, and even put a fan on the MM if it would need it.

This truck will be designed around handling well on a track.

BrianG · 02.05.2008, 03:50 PM

Also may be hard to control the equivalent of the "diffing-out" action if the front lifts. I'm sure you know what running an unloaded motor does...

Maciolus · 02.05.2008, 04:25 PM

You should also consider differenciating drag brake setting between front and rear motor.

Great project. Lot of work and setting. I keep my fingers crossed!

MetalMan · 02.05.2008, 05:42 PM

Quote:

Originally Posted by BrianG

Also may be hard to control the equivalent of the "diffing-out" action if the front lifts. I'm sure you know what running an unloaded motor does...

Good point. If only CC had an RPM limiter built into their software... Hopefully with the rear having more punch control, wheelies won't be an issue. Although a torque limiting setting would be ideal since punch control will limit mid-air control.

Quote:

Originally Posted by Maciolus

You should also consider differenciating drag brake setting between front and rear motor.

Great project. Lot of work and setting. I keep my fingers crossed!

It will be a lot of work to get it set up properly, so I too am hoping it will work well! (otherwise it'd be somewhat of a waste of time/money).

One current concern of mine is the strength of the stock diffs. Sike has been having issues even with the Hot Bodies 10/43 diffs (or at least the bearings). I might have to try out the buggy diff conversion, which could actually help because then I could use a smaller motor with a higher kv (it's been difficult finding a motor with ~500 kv, that's not too big).

For the stock Revo diffs, here's what I'm looking at for two motors:
http://www.hobbypeople.net/gallery/108522.asp kv of 480
I work there, so I should be able to get both motors for ~$100. On 5s A123 and the stock diff ratio (37/13), it should reach ~45mph, which is perfect for beating the nitros.
If I were to switch to buggy diffs (43/13), a motor of ~540 kv would be suitable, as would a motor of ~610kv for the truggy diffs (43/10)

BP-Revo · 02.05.2008, 08:00 PM

Ooo...this looks VERY interesting. Would love to see how this turns out.

BL_RV0 · 02.05.2008, 08:10 PM

why not just replace the diffs with the motors?

BP-Revo · 02.05.2008, 08:44 PM

Because if he did that it would be as if he had solid axles front and rear.

BL_RV0 · 02.05.2008, 08:46 PM

whats wrong with that?

MetalMan · 09:27 PM

I'm sure that would make racing quite difficult

Besides, I need the diffs for the reduction.

jhautz · 02.05.2008, 09:40 PM

Quote:

Originally Posted by MetalMan

Good point. If only CC had an RPM limiter built into their software... Hopefully with the rear having more punch control, wheelies won't be an issue. Although a torque limiting setting would be ideal since punch control will limit mid-air control.

Possibly the R1Pro speed control would be usefull. I understand that it has a current limiter built into it rather than just a spool up timer like the CC controlers. A current limiter would act very similar to a torque control limiter.

Actually the current limiter is the reason I really want to try the R1Pro in one of my buggies. I think it could be much more effective at dialing in the power for optimum traction.

02.06.2008, 01:08 AM

Sounds interesting to say the least!
I've always pondered using a motor per wheel with a slipper on each motor as a sort of "slip diff", but this idea sounds much more involved. Can't wait to see it how it'd function.

MetalMan · 02.06.2008, 01:57 AM

Quote:

Originally Posted by jhautz

Possibly the R1Pro speed control would be usefull. I understand that it has a current limiter built into it rather than just a spool up timer like the CC controlers. A current limiter would act very similar to a torque control limiter.

Actually the current limiter is the reason I really want to try the R1Pro in one of my buggies. I think it could be much more effective at dialing in the power for optimum traction.

I'm familiar with that feature of the R1 Pro. Unfortunately, it is much too expensive, especially for me to use two of them.

Quote:

Originally Posted by E-Traxxer

Sounds interesting to say the least!
I've always pondered using a motor per wheel with a slipper on each motor as a sort of "slip diff", but this idea sounds much more involved. Can't wait to see it how it'd function.

Only potential problem I see with the "slip diff" is it not being able to handle enough torque. But if that could be worked around, then it should work great.

Dagger Thrasher · 01:55 PM

Wow, this sounds excellent! Best of luck with this man...I'll be watching this intently. I have a React as well, and Cold Fusion (my dual BL Dagger) actually has a very similar setup with front and rear motors so this will be especially interesting for me. It's not setup as advanced as yours is going to be though, by the sounds of things.

By the way, just as an idea, maybe you could use a custom cutoff-voltage as a rudimentary current-limiter/traction control? When the cells are under load and the voltage dips, you could have a custom cutoff that activates when the cell voltage drops to a certain level. I don't know how the A123's behave though, so it might not work so well.

This should be awesome...have fun with it man.