16 x 16 Crawler Build Electronics (will this work?)

[MagnusX]

As the title says, I'm building a 16-wheel crawler ...and electronics is not my strong point (I'm better with the mechanical side of things).

It's going to have 8 x axles. I have bought 4 x Killer Crawler II kits from RC4WD for this project (only using the wheels and axles really ...might use the shocks but not sure at this stage). I actually bought these a few years ago ..but my business has been "challenging" for the last few years so the project had to take a back seat.

My electronics knowledge is really weak to be fair.

I've not bought any electronics for it yet. Need 8 x motors (I believe the 750 size will fit going from the website) - one for each axle.

I'm also planning to have one servo per axle for steering. So each axle will have 1 x motor, 1 x steering servo, 1 x battery (for powering these).

This is where I get stuck...

Do I need an ESC for each axle?

I'm assuming I can use one receiver for the whole setup?

Thank you in advance for any help or guidance you can provide.

Have attached a picture of two of the axles (everything else is still in boxes as there is a LOT of stuff in these kits ). Please excuse the dirt and dust in the photo ...it's a workshop. :-)

EDIT: Might have to add another servo per axle so I can (dis)engage the diff locks.

[Greatscott]

Questions... so many questions...

First, what radio are you planning on using?

Are you planning on all eight axles steering? If so, will they all be slaved off of one channel, or are you wanting to be able to crab it?

Are going to want any kind of dig control?

Are you planning on crawling with it?

What kind of speed are you wanting?

What kind of body, and how heavy do you think the whole mess will be when you are done?

What size/type of tires are you panning?

What is your plan for batteries? 2S, 3S, 6S?

[MagnusX]

Thank you for the reply GreatScott!

Answers to your questions...

First, what radio are you planning on using?

I have two radios I can use. A Hi-tech Lynx 4S and a Radiomaster TX16S


Are you planning on all eight axles steering? If so, will they all be slaved off of one channel, or are you wanting to be able to crab it?

I'm in two minds over this...

Option #1: Lock the steering on the axles and have servo-driven articulation between one axle and the next (if that makes sense)

or

Option #2: Still have the articulation as in the above option ...but not powered. Then, say I turn right on the controller, have the front 4 x axles steer right ...and the rear 4 axles steer left (hopefully this makes sense too)


Are going to want any kind of dig control?

I'm not sure what that is sorry.


Are you planning on crawling with it?

Ideally I want to be able to crawler almost anything (ideally taking it down to the large rocks on the beach to scale those)


What kind of speed are you wanting?

Not too fussed about speed. It would be a nice-to-have though.


What kind of body, and how heavy do you think the whole mess will be when you are done?

I don't really have plans for any sort of body. Just naked I reckon.

The axles weight: 1.4kg (3lbs)
Each wheel/tyre weighs: 1.65kg (3.6lbs)

So 8 x axles and 32 x wheels/tyres (see answer to next question) = 64kg (141lbs)

So I'm guessing once motors, servos, batteries and the linkage/articulation that I'll make to hold it all together then it might be up near 80 to 90kg (175 to 200lbs)


What size/type of tires are you panning?

Here's the tyres I have installed on a couple of the axles:


NOTE: The Killer Krawler II kits I bought came with wheels/tyres (16 wheels/tyres in total). But I bought an additional 16 x wheels/tyres like in the photo. So I have 32 x wheel/tyres for this project. I thought this thing would look kinda weird being so long and narrow ...so I'm planning to double every tyre (making spacers is not a problem as I have a lathe ...or the CNC mill might be easier for this).


What is your plan for batteries? 2S, 3S, 6S?

This is where I'm totally clueless to be honest. I don't know.

[Greatscott]

WOW, that is going to be a big girl... You are really getting out of the scale of what we normally use for this hobby, as such, you'll likely need better help than we can give you.

Initially, I would go with one ESC per axle, and will likely have to run, at a bare minimum, one 770-sized motor per, if not bigger.

You are looking at 1/5 - 1/4 scale servos to push the steering on each axle. The servos alone will need their own power supply, I double if an ESC-s BEC will be able to push one effectively, to say nothing about all four.
I would set the steering up with three basic modes:
1: Drive- The front sets of axles steer, the back sets face forward.
2. Military- The back axle sets turn opposite of the front axle sets. If the front is pointing right, the back is pointing left, this is reduce turning radius.
3. Crab- The front and the back axles turn in the same direction. This is good for obstacle avoidance.
No matter what, you will want to set each axle up on its own channel, then have that channel slaved to a primary steering channel. Because each axle will have a different steer (turning) rate, connecting the servos to a Y-harness will not work. So, assuming you are in "drive" mode, and only the front four axles are used for turning, your back axle in this group will be the master, and the four in front of it will be slaved to it. Each of the slaved axles will turn a bit less than the one behind it so that their turning arcs match on the chassis, this is all set up in the radio.

For power, I would start at 4s as a bare minimum for a battery, but might want to crank it up to 8s.

Given the weight, I do not believe any kind of a dig will be practical, so I wouldn't worry about that now.

[ferp420]

ive had good.luck with the johnson 775 motors there only $15 ish and ive been running the new rain 480 esc $20 with those motors the combo is good for 4s as long as you dont try to run the internal bec at the same time

https://www.ebay.com/itm/JOHNSON-700...-127632-2357-0


https://www.ebay.com/itm/480A-3-Mode...-127632-2357-0

[MagnusX]

Originally Posted by Greatscott

WOW, that is going to be a big girl... ... ...

Thank you for the feedback GreatScott - this is incredibly helpful!

So I have a couple of questions...

I'm guessing the only limitation with putting the biggest motor I can on the axles is the physical limitation, right?

One ESC per axle sounds good - can do that.

You mention different modes for the steering. However, I like the idea of the military style. Can I just confirm that doing military style with eight axles means if the front axle turns right, then the rear axle will simultaneously turn left essentially ...and all the six axles in the middle will have no servos or active turning ... they will just follow the front axle (just a motor powering the wheels)?

I'd ideally like to go for the biggest drive motors, biggest servos and ...well biggest everything I can. Don't want to have any limitations. Not bothered about breaking things... can alway beef them up later (I work mostly with titanium in the CNC shop).

Will have a look at motors today and see how big I can go and what makes are good. If you have any recommendations that would be most appreciated. Thank you for your help once again!

[MagnusX]

Originally Posted by ferp420

ive had good.luck with the johnson 775 motors there only $15 ish and ive been running the new rain 480 esc $20 with those motors the combo is good for 4s as long as you dont try to run the internal bec at the same time ... ...

Thank you . I will take a look at these. Truthfully, I'm a little apprehensive of a $15 motor on a project such as this though.

[ferp420]

Originally Posted by MagnusX

Thank you . I will take a look at these. Truthfully, I'm a little apprehensive of a $15 motor on a project such as this though.

johnson replaced mabichi as the silver can motor maker but hay you can pay 4 times as much for the same motor with a traxxassss sticker on it or dewalt sticker i dont think ive seen any other manufacturers of silver cans anymore i know my last tamiya kit had a johnson silver can motor in it



those are my go to motors for all my 1/6 and 1/8 scale builds for years now i have one thats going on 5 years now with out issue

[Voodoobrew]

Making a Truckapillar?



You only need one ESC for multiple brushed motors provided it has the amperage to push all the motors. You can also do a bunch of smaller ESC's and just split Ch1. I don't think 16 motors will pull 16x the amps, because each motor will not be pushed as hard, since they are all helping each other. So like one mamba monster X might work with higher turn motors in a Crawler. Really you need to know the amp draw to know what the ESC, requirements are. You could also run one ESC for the front 8 axils and one for the rear. lots of ways to save here. You can start with one ESC, then split Ch1 and add more until the ESC's cool down and you don't reach the amp limit. You can monitor the amps with Castle software as you do it. Don't worry about over/under drive the axles that you want to go slower generally do because they are under load.

Running those big dualie wheels and tires will be hard on the axles and servos.
For the steering you can program an Arduino or raspberry pi or esp32 or similar to take the input steering servo and reverse and reduce it for each axle. You could even program it to work with a 3rd Ch to set which axle it rotates on, if you have a mind for it.