Low speed, hi torque 4 motor fwd/rev project

Greetings to Everyone,

I am looking to get some feedback on a project I am working on. I am building a low, wide radio-controlled vehicle to move around large bins carrying debris. The plan is to use a vehicle with “crab steering” to go underneath a bin, clamp onto it and then move it to a desired location. This is not a skateboard and is not intended to be ridden by a person.

Wait- what’s that? Why am I here then? Well… because I am using just about all of the components involved in building an electric skateboard. As such, I wanted to share some info and hopefully get some feedback and helpful hints from those who have more experience.

-The idea is build a frame in the shape of a rectangle, and use four 120mm Flipsky All Terrain wheels.

  • I will also be using the Flipsky 5M 40T Belt Pulley gear (on each wheel).

  • (4)Flipsky 6384 190kv motors will be used along with a 16T pulley on each motor

  • (2) Flipsky Dual FSEC 6.6 controllers will be used along with a PWM/PPM signal converter module for each

  • A 6 channel RC surface radio will be used to control the vehicle

  • Battery will be only 12v heavy SLA batteries for needed weight, simplicity and endurance

That is a preliminary list of components. I will also source items such as connectors, motor mounts, drive belts etc. as parts arrive and the build comes together.

I do have a few questions about the plan listed…

  1. Has anyone ever used the ESC’s in a FWD/REV situation? I realize that it would not be normal (much less desired for skateboard use) intended use of such items.

  2. My calculated top speed with load is 18.7 km/h or 11.62 mph. Torque should be adequate to turn or move a bin rolling on large swivel castors. Does anyone see an issue with the belts, or pulleys holding up to such an application?

Any input or helpful information would be greatly appreciated.

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Are you an FRC alum?

I designed a custom swerve if you want any ideas for cheap easy ways to design the coaxial drive or slip rings.

just lmk.

I am not an FRC alum. And I might need a bit of translation as to what a “custom swerve” is. The design plan is to have 4 independent motors/wheels each mounted on independent axles.

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How do you plan to steer, with wheel slip?

Does your remote handle this, or do you need a converter to change the RC signal into separate wheel speeds.

I think you might want higher gearing. Even on 2x6384 it can be difficult to pull away from stopped on an incline. Since you have heavy loads, I think you will be better off with higher gearing (a larger wheel Pulley or smaller Motor Pulley)

How do you plan to steer, with wheel slip? - Yes, the plan is to use either the left side or right side wheels to steer. A converter is included in the list of parts to change a PWM (RC signal) to PPM for the controller. Since the controllers are made for dual motors, each controller will be used to control the front and back wheels on either side.

Regarding the ability to move: I’m using (4) 6384 motors and will not use the vehicle on inclined surfaces beyond a mild slope. As well, the vehicle will not be loaded with weight on top of it, but will rather “push” or “pull” a wheeled cart filled with debris from underneath. Even still, I will purchase some 10T pulleys just in case. The top speed with a 10T pulley (15.38km/h or 9.56mph) is still within range of what is needed.

I hope this helps to give more context:

image

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Custom swerve being I have designed a Swerve drive not just purchased it off the shelf.

When you said crab drive that is a kind of swerve without independent module rotation allowing spinning without wheel scrub.

So yeah I can tell you how to make your own on the cheap-ish

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Fascinating! And yes I am interested in learning about how to make my own. One thing I notice is that the swerve assembly has the motor mounted vertically. In order to go underneath the bin I need to transport, I have a maximum clearance height of 16cm.

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You would need a more complex mechanism to turn wheels without using vertical height.

Could you have the robot only going under from one side? then you could use a pair of steering wheels, this would make it drive like a forklift with rear wheel steering, and give you an edge to push against.

This would reduce your tyre scrub compared to if you skid-steer all four.

image

This is the exact robot I designed. If you look at the design it is easy to move the motor sticking up to below just with a tiny design change.

If I had to guess a price you can make a swerve/crab drive for under 1K on the cheap. Motors included maybe.

you just put a bearing in a bearing and use the inner shaft for wheel power

My design was overbuilt as heck as I was planning on mounting a chair on it and riding it around. it could probably support a shit ton of weight. steering bearing rated over 1200lb at least.

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@Louis Could you have the robot only going under from one side? That’s exactly the idea I had in mind and a similar shape of the frame with as well. The bins are normally stored against the side of a building and the accessible side (front) is the long portion of the bin. Once underneath and pressed against the bin, the vehicle’s frame will extend past the back side of the bin where folding arms will capture the bin. When the bin is transported to it’s destination, the arms will fold flat and the transporter can then be moved in reverse out from under the bin.

@Fosterqc I did some digging on swerve drives and saw some examples where the motor was mounted below or at a 90 angle towards the side. I’m very interested in trying it as the cost point is within my project budget.

I am very thankful for all of your replies, and information might I add.

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if you read my post above and look at how it is design it would be remarkable easy to move the steering motor below which is exactly what I said.

The bevel gears are the harder to mfg part. I have one idea where you just put lipo packs and motor controllers and radio receivers inside the wheel modules, might cost more than bevel gears with all the batteries and wireless but idk.

If that sounds bad to you I am also designing one with electrical slip rings.

@Fosterqc Indeed I saw your post and do realize how simple it would be to mount the steering motor below the swerve assembly with the shaft of the swivel portion extending above allowing space to mount a pulley or gear on it.

Bevel gears are used in a wide variety of other applications, perhaps I can source some that would suffice for this as well. With regards to the batteries, I will stick with heavy SLA batteries for this project.

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