I really want to build up a BRUSHED Mini-Z to run in 2wd Mod...

[lambdapriest]

It's probably not the best idea; but I can't stop thinking about it.

I want to build up a weapons-grade Mini-Z, running on a brushed motor, to run in the 2wd Mod class (against the lipo chassis cars).

Why?

• I think I could do it pretty cheap (famous last words, I know)
• It would be great fun to watch my little MR03-based car pull on the lipo boys down the back straight, even if I wasn't as fast on the rest of the track (when my club sets up for Mini-Z, we have a 30-plus-tile-long back straight and yes, it's incredible)
• I love the sound and feel of driving a brushed motor

I already have an MR03 that's part of the way through this conversion process - I picked up a PN 43t and bolted it on to the MR03 board, and the car's already pretty fast; but I want to go bigger.

Here are my constraints:

• I really don't want to build a chassis car; I already have an MR03, and I'd be open to converting it to a PN 2.5w, but I want to keep the "plastic chassis that's not a true pan car" thing going
• Which means that I need to run a servo controller that supports a 5-wire servo, so I can use the servo motor / gears / potentiometer that are already in the chassis
• I want to run a brushed motor

For the motor, I've found that PN makes a 31t brushed motor. I'm not sure how much faster it'd be than the PN 43t that I already have, but I have to imagine that it'd be quite a bit more punchy. I don't think I can safely wire it up to the stock MR03 board without FET stacking - which is above my pay grade.

I'd like to run it on "2s" - i.e., four of these PN Extreme Power Li-Ion 3.7v AAA-sized batteries. I know I'd have to re-wire the battery holder to make it 2s2p - that's not a big deal. It'd be easier if I did a PN build out of it, but I'm sure I could get it to work on the MR03 chassis. That definitely takes "just use the MR03 board" out of the realm of possibility - I would definitely melt it.

Furitek makes a board called the Velos that supports the 5-wire servo and is a drop-in replacement for the MR03 board... but it's brushless. I'll probably go this route if I have to give up and run brushless, but I don't want to!

So what I need, I think, is:

• A brushed ESC (easy)
• A receiver (also easy, I already have a Flysky micro receiver sitting in a box in my office; I'll get around to installing it in the SCX24 eventually)
• A servo controller that supports a 5-wire servo (haven't found one yet), OR advice on how to mount up a normal 1/28 servo on an MR03

I recognize that this probably sounds a little bananas. Maybe typing it all out will help me accept that it's an objectively bad idea and move on; but if anybody has any advice, I'd love to hear it!

EDIT:
HOLD UP, the game may be afoot:

https://www.rcgroups.com/forums/showpost.php?p=37009285&postcount=8

From reading this thread - it sounds like I can use the board from a 3-wire servo to control a 5-wire servo? Does that sound right?

I have a 1/10-scale AGFRC servo that I may be able to sacrifice; due to an unfortunate LocTite-related incident, the horn is permanently affixed to the splines.

I'm currently setting up my workshop in the garage; once I get that done, I might rip the thing open to see what I'm working with. Would be pretty simple (albeit time-consuming) to desolder the board, desolder the Mini-Z board, pin it all back together, and see what happens. Can anyone confirm - has anyone tried this before, running a 5-wire servo on a 3-wire receiver?

 

[remote uncontrol]

You probably shouldn’t ask me about doing a build because I’m a total sucker for bad ideas. Make sure you keep us posted if you go through with it

 

[lambdapriest]

Fair enough!

Thinking about it some more... the servo I already have, is a brushless servo. The Mini-Z servo has a brushed motor.

I guess I'm gonna give this a shot - just picked up 4 micro servos for $9 off Scamazon https://www.amazon.com/Micro-Servos...47&sprefix=micro+rc+servo,aps,109&sr=8-9&th=1

Leaving this thread open so that I can hear any advice that anybody else may have - but if nobody stops me, I'll probably start a build thread once I get the servos in, and get the time to sit down with them and rip 'em apart!

 

[tntpoof]

I would have just dropped a small lipo pack in and got the correct amp ubec and added that to lipo with a lug and then did my mods. I dont see the 3 wire servos working.but I dont run Zs smallest I run is a Vortex I modded to handle a54- size motor.

 

[lambdapriest]

What is a "ubec" and what do you mean by "lug"? Not familiar with the terminology (but then again, there's plenty that I don't know).

I'm pretty sure that I can steal the board from a 3-wire servo and wire it up to the Mini-Z's servo motor - apparently, a servo is constructed from:

1. Gears
2. A motor
3. A potentiometer to sense position
4. A controller board to drive the motor and read the potentiometer

It looks to me, like the MR03 Mini-Z board has the "controller board" part of the servo integrated into the receiver / speed controller board. If that's the case, I should be able to drive the onboard servo and read from the onboard potentiometer with a board from a 3-wire servo. The worst-case scenario is that I sacrifice a $2.50 servo.; if I'm feeling really gunshy about destroying my existing Mini-Z by blowing the board while I try to desolder the servo motor and potentiometer, I can just grab the whole MR03 board unit, which includes the servo motor and potentiometer from my club, as they're in stock and only $40.

 

[Doom!]

Sounds like you have a plan. This stuff is over my head but looking forward to seeing how it all works out.

 

[lambdapriest]

Okay, we're doing this. Let's gooooooooo https://www.rctalk.com/forum/threads/2wd-mod-brushed-mr-03-mini-z-build.139580/