Controlling multi-motor vehicles?

[Roog]

Hi, fellow modellers! I have another daft question, sorry, but I don't know who else to bother with this question.

I am designing a 3 1/2" gauge 'diesel' (Nitro IC) electric locomotive, and whilst it is common to use a 'wired connection' between the hand controller and the loco drives I would prefer to go with RC, just in case the loco is unable to pull passengers.

The basis of the design is a 15 to 20cc nitro engine driving a BLDC motor operating as a motor generator, the motor is controlled by a VESC, allowing remote engine start and generation to power the model. The motor generator is able to charge a battery via its VESC, so really its a hybrid. Drive to the loco is via 4 No. smaller BLDC motors mounted on each of the wheel axles in the bogies at each end of the loco.

The RC needs to control a servo to control the throttle on the IC engine, a switch to switch power to the glow plug during start, a channel to operate the VESC to determine the load on the IC engine, charge the main traction battery and to provide power to the 4 No. bogie mounted axles. I am using small out runner sensored motors for the 4 drive motors, each one will require its own ESC, yup its beginning to sound expensive! I was thinking that once calibrated all 4 axles need to be driven at the same speed and in the same direction!

My question is can I wire all four ESCs to the same output channel on the RX? Or would it make sense to wire each ESC to a separate channel and link them via the RC configuration? (BTW I'm not sure this is even possible)

Your help and experience would be gratefully received.

I am also interested in any other foreseeable issues with this daft idea, such as the VESC and 4 No. ESCs all connected to a common traction battery? I plan to provide the RX with its own dedicated battery supply.

 

[RetroThutmose]

Radiomaster has completely customizable channel mixing and configuration. I would look at the mt12 or some of their cheaper stick radios.

 

[Roog]

Radiomaster has completely customizable channel mixing and configuration. I would look at the mt12 or some of their cheaper stick radios.

Thank you @RetroThutmose, sounds like you prefer the idea of each ESC on its own channel? I like 'cheap' especially as the loco can't really get very far away on the club track.

 

[WickedFog]

Thank you @RetroThutmose, sounds like you prefer the idea of each ESC on its own channel? I like 'cheap' especially as the loco can't really get very far away on the club track.

You could run 4 ESC's off one channel, provided only one ESC has it's BEC connected to the Rx. But doing that won't allow you any controllable way to time the 4 motors together. With channel mixing as Retro suggested, with the aid of an RPM meter you could fine tune each motor's signal so they are all running as close to the same speed as possible. I think anyway lol.

This sounds like a ridiculously complex build, so hell yeah man, let's go. I've never heard of a true remote control train either, so this will be a fun build to watch.

The Radiomaster MT12 is a kickass radio, running EdgeTx, which is an open source firmware, with a large community of users. And since it is open source, it's that community driving it's ongoing development. It gets updates fairly regularly, so it just keeps getting better. It's a handful of a radio to learn initially, but it also is a radio that is damn near infinitely customizable. For what you're going to be using it on, it's the radio I would get.

If you have Discord, here is the EdgeTx discord channel. There are a lot of folks in there happy to help. Just be prepared though. It's an overwhelming number of uber geeks all hanging out in one place
https://discord.gg/7Y56mcJT

Some info on the MT12, with some links to tutorials and other resources.

Thread 'Radiomaster MT12 - Review and Guide'

Sep 22, 2024

Introduction

@Lostinthewoods86 sent me this radio for scientific purposes. So as I learn more about it I am going to use this thread to document things I figure out with this amazing radio.

Here is everything you get, and currently, you can grab this radio for around $130 from various online shops and retailers, as well as Amazon.

​

Description​

The RadioMaster MT12 is a pioneering open-source surface radio, and the first surface radio officially supported by EdgeTX, ExpressLRS, and the Multi-module project. Boasting 10 physical inputs...

• WickedFog
• Replies: 81
• Forum: Reviews, How-to, & Guides

• 
• 

 

[tudordewolf]

Since it happens to be 4 motors, you could use a 4-in-1 ESC and save some bulk. Its exactly what it sounds like, 4 ESC's on a single board.

They're made for quadcopters so the timing would be consistent between all 4, you could feed all 4 the same input signal, and it would only need 1 "power in" rather than a bulky distribution harness. You'd have to give it a heatsink and fan.

I'm planning on using one for a C-130 RC build, driving it with a single throttle channel.

I dig the hybrid starter/generator, I want to develop a starter-alternator for my RC planes.

 

[CertifiedMike]

Any Arduino gurus out there?

The MT12 idea sounds like a good idea. I don't know much about newer radio tech...

I'm watching to see what the solution is.

 

[1/48 fleet]

I think that tudordewolf offers the best solution regarding how many ESC's to use and how to "channel" them. If using multiple ESC's, regardless if they are Y'd together and run from a single channel, or if they run from multiple channels that are mixed by the transmitter, you run into the problem of timing them all together properly. I suspect that at least one will always be out of phase., hence tudordewolf's elegant solution.
As complicated as your set-up sounds, I would lean towards a separate supply battery for your radio. The is no reason why you could not add a charging circuit to it as well, but I would doubt that it is needed given the battery choices available.

 

[RetroThutmose]

people on the mt12 facebook group have said chatgpt can help make scripts and stuff. i haven't tried it myself.

A poster said he used cahtgpt to program a launch control, ABS, and a pit lane speed cutoff. Programming for drag racing but just an example of what can be programmed.

I'm curious if timing the motors would make much of a difference. i assume a train isn't going to be turning a lot of RPMs and is more about torque. i guess it depends how they are geared tho.

 

[CertifiedMike]

people on the mt12 facebook group have said chatgpt can help make scripts and stuff. i haven't tried it myself.

A poster said he used cahtgpt to program a launch control, ABS, and a pit lane speed cutoff. Programming for drag racing but just an example of what can be programmed.

I'm curious if timing the motors would make much of a difference. i assume a train isn't going to be turning a lot of RPMs and is more about torque. i guess it depends how they are geared tho.

Even if they are all connected and timed today, at some point 1:1 must have been running a non-(timed), snychd? system.

How important is perfect timing?

The drone controller seems like its already built to overcome most of the obsticles.
A capable radio to control this and possibly the next 'crazy train' projects @Roog comes up with seems like a smart idea as well.

 

[tudordewolf]

I don't think the timing is that important, as long as the motors are spinning together the ESC's will adjust their timing so each one is "pulling" approximately as strongly as the throttle input, they have to do that anyway in flight for varying loads. That is, once the train is in motion. Before it's moving, all 4 ESC's may have cogging issues, whether or not they're separate or a 4-in-1.

Sensorless ESC's for prop-driven motors have an automatic 'startup' sequence that's supposed to get the motor moving enough to generate some back-emf so the ESC can read the coil positions and start driving the motor. (the effectiveness of this sequence sets apart cheap and quality ESC's, the cheap ones take longer to "get going") - however, the motor has to be able to turn freely enough to pass through a few phases from just that initial "kick", if it's under a lot of load, like pulling a train, the ESC might not be able to get into its "groove"

A locomotive application would really benefit from field-oriented control, basically what the VESC on the generator side will be doing, to would allow it to produce a lots of torque at low RPM's without burning itself completely out. That's the hard part for a locomotive. You sort of want crawler motors, but you'll want them in a size not really... "available".

Hoverboard motors though, are cheap, torque-y, good for about 350W a pop, and would probably be converted to your locomotive application pretty easily, and they already have hall sensors.

 

[Roog]

Thank you everyone, its really helpful to have input from experienced users.

A bit of back ground, I am from a generation (I was a teenager when I got in to RC) when we had 27MHz sets where the technique to get rid of self centering sticks was to open the TX up, remove the spring and tighten the stick axis gimble screws a little. I find these new configurable RC sets a bit intimidating and talk of coding not especially attractive. However I do appreciate that lots of the new features could work in my favour and with the growth in DIY drones I am hopeful that there will be people out there that can help.

I was planning on using 'hardened' Outrunner skate board motors like the Flipsky 5048, they and their gearing (4:1 should be possible) have to fit between the wheel flanges and this is tight. Whilst it is common practice to link the two axles per bogie by belt or chain and use just one motor there isn't much room to fit this in, so I have elected to go with one motor per axle.

Top speed is 8mph, which requires max axle speed of 1000rpm, hence gearing and motors with good torque is important

I am not too worried about strict synching of the motors as I am hoping that the weight of the loco with lock them in synch. My calculations suggest that 600W to 800W all up should be adequate to haul a few passengers provided the loco has sufficient traction with the rails, and less once moving on the flat.

Whilst waiting in the Hospital waiting room yesterday, I did wonder if a drone set up would work, afterall it would use one battery and at least 4 motors, I would just need them all to operate at the same speed and time!

Two key issues bother me, are 1. pulling together a sensible ESC system to drive the traction motors, (I was going to use sensored BLDC motors for realistic low speed control) and 2. the set up and use of an VESC / BLDC motor and IC engine, say an OS90 to act as the generator. This sounds tricky to me.

I have seen Youtube vids of people doing just this but they are short of details. I was encouraged by Drone flyers using IC generators in their hybrid drones, but these, understandably tend to be on the bigger size, 2kW plus, and wont fit with in the loco body. I expect 600W would be fine to help keep the battery topped up.

Really I need to think of this as a battery powered, electrically driven loco with a very noisy IC powered battery charger strapped on its back :0)

I will see what the drone boys have to say, you might hear the laughter from here!

 

[CertifiedMike]

Thank you everyone, its really helpful to have input from experienced users.

A bit of back ground, I am from a generation (I was a teenager when I got in to RC) when we had 27MHz sets where the technique to get rid of self centering sticks was to open the TX up, remove the spring and tighten the stick axis gimble screws a little. I find these new configurable RC sets a bit intimidating and talk of coding not especially attractive. However I do appreciate that lots of the new features could work in my favour and with the growth in DIY drones I am hopeful that there will be people out there that can help.

I was planning on using 'hardened' Outrunner skate board motors like the Flipsky 5048, they and their gearing (4:1 should be possible) have to fit between the wheel flanges and this is tight. Whilst it is common practice to link the two axles per bogie by belt or chain and use just one motor there isn't much room to fit this in, so I have elected to go with one motor per axle.

Top speed is 8mph, which requires max axle speed of 1000rpm, hence gearing and motors with good torque is important

I am not too worried about strict synching of the motors as I am hoping that the weight of the loco with lock them in synch. My calculations suggest that 600W to 800W all up should be adequate to haul a few passengers provided the loco has sufficient traction with the rails, and less once moving on the flat.

Whilst waiting in the Hospital waiting room yesterday, I did wonder if a drone set up would works, afterall it would use one battery and at least 4 motors, I would just need them all to operate at the same speed and time!

Two key issues bother me, are 1. pulling together a sensible ESC system to drive the traction motors, (I was going to use sensored BLDC motors for realistic low speed control) and 2. the set up and use of an VESC / BLDC motor and IC engine, say an OS90 to act as the generator. This sounds tricky to me.

I have seen Youtube vids of people doing just this but they are short of details. I was encouraged by Drone flyers using IC generators in their hybrid drones, but these, understandably tend to be on the bigger size, 2kW plus, and wont fit with in the loco body. I expect 600W would be fine to help keep the battery topped up.

Really I need to think of this as a battery powered, electrically driven loco with a very noisy IC powered battery charger strapped on its back :0)

I will see what the drone boys have to say, you might hear the laughter from here!

I ultimately bought an NB4+ radio over an MT12 due to the set up, programming and need for computer connection.
I enjoy RC but I'm not trying to rewire the hobby!
I also came from 'simple radios'. Firward, back, left, right...
My first RC's were mechanical escs. Not even brakes to set up!

Sounds like the drone set up might be the way to go.