MOW - Motor on wheel crawler

[Unboxingexperience7]

Hi guys,

this project was for a long time on my mind. I always wanted to build a crawler with a wheel hub motor. Finally I found electric components which seem to suit. I have already tested servo driven wheels, which was quite problematic. Now I m going for brushless gimbal motors.

So let's start with the setup. I decided to use brushless gimbal motors as they provide torque and direct drive at a small size. I was searching a long time for a ESC which can control these motors. You can't use normal brushless ESCs. I bought 2 of these special gimbal ESCs, 1 per axle.

All of the parts for the axles are 3d printed. The axle is a simple aluminum tube. At the moment I'm testing the design, so it will take a few days until I m finished. However, I think it is time to share with you my design and maybe get some useful feedback.

Here you can see the state of play: https://youtu.be/oREFFpP1Qxo

[aircooled]

Since years I'm thinking about MOW crawlers and never thought about gimbal motors. Great idea, looking forward to see how this will end up

[jebster]

i know of several people who have been looking into this. from what i've hear the big challenge is sufficient torque without the benefit of gear reduction and control of the motors. how do you get motors to move together effectively if loading wheels separately?

looking forward to someone showing a working model, even if it is just a proof of concept.

[waka789]

Subbed I want to see this

[JohnRobHolmes]

I'll be interested to see how they work for you, its a really cool project and I've never committed myself to action. The high resistance of gimble motors will be your main enemy when trying to squeeze out power.


The basic difficulty is because of low rpms. A regular drivetrain will have about 35:1 reduction. To have a motor with equal torque without this reductions requires equal terminal resistance and 35x lower KV. So a 3500kv system is now 100kv. You can extend the motor length 35 times, or increase motor diameter about 6 fold. Or a combination of the two that nets a 35 times increase in flux gap area. RPM reduction must always be compensated for with motor size, specifically the flux gap area.


The issue is illustrated nicely in the ebike world. A high rpm motor (astroflight 3220) that will sustain 10,000 watts forever with airflow is 4 pounds plus two pounds of reduction system. A hub motor (cromotor v3) that will sustain the same for only 5 minutes with airflow is 24 pounds. Your application is smaller, but will face the same challenges.




Keep at it and don't be discouraged by my math. At the end of the day, only real world testing will prove results. I've always analyzed myself into a corner and could never make the jump to reality.

[MountainStorm]

I hope you work it out. That was one of the first things I asked about when I joined this forum and got a much less technical reply. I'm still not savvy enough to know WTF JRH is talking about half the time but I trust him

[JohnRobHolmes]

My understanding of motors is always changing, so my response on the same subject will vary a lot

[MountainStorm]

Originally Posted by JohnRobHolmes

My understanding of motors is always changing, so my response on the same subject will vary a lot

You came to mind when I saw that

[JohnRobHolmes]

In the path of stopping my endless analyzing of the mow concept I've ordered some parts that I know will break. But it will be a start at least.

[adamargue]

This is going to be a awesome project. I'm thinking run a little larger wheel and make a drop box like on a portal axle and see about running a small motor. That way you can have some gear reduction.

Also have you guys thought about steering? Are you going for tank steering or standard with a servo or maybe a combo?

[jebster]

Originally Posted by adamargue

This is going to be a awesome project. I'm thinking run a little larger wheel and make a drop box like on a portal axle and see about running a small motor. That way you can have some gear reduction.

Also have you guys thought about steering? Are you going for tank steering or standard with a servo or maybe a combo?

I think you would need standard steering but given a separate drive to each wheels you could do some interesting things.

[adamargue]

Maybe we could finally have a rear cutting axle! Or whatever was supposed to be for the xr10.

[barrybelvedere]

Adding unnecessary weight to the rear of the truck hinders performance all around. Keep it simple and light weight.

[Savagethrash]

Any updates to your project? I am very interested in hub drive crawlers but lack the math skills to calculate the size of motors, windings, stator and pole counts to actually make it happen.

[BC-Brian]

Cool Video. I like the servo placement.

I have been looking/thinking about a MOW setup for nearly 2 years now. I looked into the gimble motors a while ago, the mechanical package and allure of no gearbox is to fantastic not to investigate. The calculations I ran based on what I could find for gimble specs gave me concern that it would not have sufficient torque. Have you tied this thing together and tried running that axle around yet??

[Szczerba]

Very cool setup.

Originally Posted by barrybelvedere

Adding unnecessary weight to the rear of the truck hinders performance all around. Keep it simple and light weight.

Said the guy to the guy that invented MOA crawlers about shaft driven truck when he posted a video on RCC years ago.

[phishead1101]

What if you went a different direction with the MOA and left the motors in the chassis? Might give you some more room for gearing?

[RickBinSJ]

how about a portal axle type gearbox? you'd get some room for gearing and get the motors a little higher up too

[HumboldtEF]

gonper worked up a design that is portal like. Unfortunately Photobucket ate the pictures. He got pretty far along prototyping but I think he gave up or just stopped posting.

Lots of work and refining are still needed I believe.

Crazy axles idea design