Motor mount question

[Pito Salas]

I am building a small indoor model, differential drive, two wheels and a caster. Very standard,

The base is made of 3/16 plywood. I want to mount the motor on the top surface of the base so it doesn't take away from the ground clearance. The motor bracket I have is a simple L-piece with four holes to screw to the base and two holes to screw to the motor. The wheel I have right now is 6cm diameter.

With that combination I get almost no ground clearance.

My option is to get a much bigger wheel.

Are there other options? For example if the bracket had less (or no) clearance between the motor and the plywood, this would gain me maybe 1cm of clearance. But still not much.

Any other suggestions?

[camp .]

> Any other suggestions?

    Can we get some photos? - cp

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[Pito Salas]

Here are some photos. This is a very basic question. As usual I am digging around to see what exists that I don’t yet know about:

First picture shows the motor with the bracket attached to the base:

Second picture shows the clearance if I have the motors under the base. Good ground clearance but I prefer not having the motor exposed.

Their photo shows the base set up so the motors are on top. The ground clearance is next to nothing.

Pito

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[Marco Walther]

On 1/17/25 07:25, 'Pito Salas' via HomeBrew Robotics Club wrote:
> Here are some photos. This is a very basic question. As usual I am
> digging around to see what exists that I don’t yet know about:
>
> First picture shows the motor with the bracket attached to the base:
>
>

> IMG_1904.jpeg
>
> Second picture shows the clearance if I have the motors under the base.
> Good ground clearance but I prefer not having the motor exposed.
>

> IMG_1905.jpeg
>
>
> Their photo shows the base set up so the motors are on top. The ground
> clearance is next to nothing.
>

> IMG_1906.jpeg
>
> Pito

You have
30mm from the axle to the ground (wheel diameter / 2)
- 5mm plywood
- 12.5 mm motor radius
- let's say 2.5mm for the bracket

--> you should see < 10mm clearance?

Your choices are
* question, how much clearance you really need
* larger wheel diameter
* put the motor below the base (potentially with some cover). Next to
the wheel, there is usually not so much of a problem.

Attached are some pictures of an old robot with the same motor (and
probably a very similar bracket) and 70mm wheels. That gives me 16+mm of
clearance.

-- Marco

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[James H Phelan]

6cm = 2 3/8" dia = 3cm or 1 3/16" radius = ~1" clearance subtracting for unknown axle diameter.

Enough for a tablebot or floorbot if unobstructed.

Could have issues w/ door sills, thick rugs.

Mount the wheel axle under the base and drive via gear/belt/chain from the motors above the base.

Mount the motors below the base with a 90o angle gearbox to minimize the width percentage of clearance interference.

Get bigger wheels.

However bigger wheels = higher torque (force x radius) = bigger motors = bigger battery = larger volume = more weight = ....

RoverDoc

James H Phelan
"Nihil est sine ratione cur potius sit quam non sit"
Leibniz

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[James H Phelan]

The "classroom standard" BoeBot has 3/4" clearance.

The Stingray, its out-of-production big brother, has 3/4" less the height of thumb screw heads I use for convenience.

James H Phelan
"Nihil est sine ratione cur potius sit quam non sit"
Leibniz

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[Chris Albertson]

In every case you will have the greatest ground clearance if the motor is mounted to the BOTTOM of the plywood.  The clearance will be (wheel diameter - motor diameter)/2.0

With the motor on top of the plywood you get  ((wheel diameter - motor diameter)/2.0) - (plywoodthickness+mount thickness)

The above is true as long as the wheel is directly mounted to the motor shaft.  To do better is hard because you would beed a more complex drivetrain.

SO you are correct, wheel diameter is what matters.  The bigger the better for ground clearance.      

But now with the big wheel you are going to have to run the motor slower for the same speed.   Be sure and work out the moter RPM vs robot speed.  Ususaly with simple DC brushed gear motors thery have a minimum usfull RPM and with big wheels the minimum robot speed can maybe be faster then you’s like.

Again, you get the best clearace wit the motors on the bottom.

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[Chris Albertson]

If you are worried about having the moter exposed to bumps. Place crash bumpers around the motor. Or 3D print the motor mounts and design them to suround the motor so ther motor fits inside a hole in the plastic. so the mount does double duty as “armor”.

[Pito Salas]

Thanks all. I thought I might have overlooked a different way of mounting the motor. One correction to Chris’ formula (IMHO) 

(wheel diameter - motor diameter)/2.0

Assumes that the motor is sitting flush to the surface and all mounts I’ve seen have a 1-2 mm gap there. But I will mount the motor on the bottom as it seems is the usual practice in my kind of scenario!

Pito

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[Chris Albertson]

I will argue that the formula is correct event with a very think mount.  Because if the motors are under the plywood,  the ground clearance is defind as the distance from the bottom of the wheel to the bottom of the motor.  The plywood is well above the motor and a thick mount only makes it higher above the ground 

If you can print the mtor mounts then they can be wedges that lift the robot upward on collision.

[Rafael Skodlar]

Pito,

The following three options are worth exploring as well:
- mount the motor in vertical position. You can buy motor/wheel
mechanisms of different sizes that come with different gear ratios.
The wheel itself can be 3D printed plastic [1] to fit your needs.

- use flexible steel cable in the flexible steel pipe between the
motor and the wheel. That's literally the most flexible solution.
Bicycle brake cable might work on small robots.

- use a cardan shaft between the motor and wheel.

- my favorite: the motor with a built-in wheel.

One source of many parts are hobby stores that sell remotely
controlled cars or parts to make them.

[1] The silly world wrongfully calls that kind of manufacturing method
3D printing. It's 3D plotting. I can prove my statement with my
"drafting robots"; HP 7221A PLOTTER and HP 7475A PLOTTER that can make
pictures with ink instead of plastic filament. Same footprint [2], on
paper, but only one layer of ink.

[2] one time it's print, other times it's draft, or drawing, ...This
language is so messy, no wonder AI and I are so confused because
there's no logic to it.

Back to repairing two 3D plotters...

Rafael

On Sat, Jan 18, 2025 at 7:01 AM 'Pito Salas' via HomeBrew Robotics

Club <hbrob...@googlegroups.com> wrote:
>
> Thanks all. I thought I might have overlooked a different way of mounting the motor. One correction to Chris’ formula (IMHO)
>
> (wheel diameter - motor diameter)/2.0
>
> Assumes that the motor is sitting flush to the surface and all mounts I’ve seen have a 1-2 mm gap there. But I will mount the motor on the bottom as it seems is the usual practice in my kind of scenario!
>
> Pito
>
> On Jan 17, 2025, at 2:10 PM, Chris Albertson <alberts...@gmail.com> wrote:
>
> If you are worried about having the moter exposed to bumps. Place crash bumpers around the motor. Or 3D print the motor mounts and design them to suround the motor so ther motor fits inside a hole in the plastic. so the mount does double duty as “armor”.
>
> On Jan 17, 2025, at 7:25 AM, 'Pito Salas' via HomeBrew Robotics Club <hbrob...@googlegroups.com> wrote:
>
> Here are some photos. This is a very basic question. As usual I am digging around to see what exists that I don’t yet know about:
>
> First picture shows the motor with the bracket attached to the base:
>
>
>
> --
> You received this message because you are subscribed to the Google Groups "HomeBrew Robotics Club" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to hbrobotics+...@googlegroups.com.
> To view this discussion visit https://groups.google.com/d/msgid/hbrobotics/95D2E1FE-032D-41DB-A4AE-3D24E2822AD5%40gmail.com.
>
>
> --
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[Chris Albertson]

> On Jan 18, 2025, at 9:36 AM, Rafael Skodlar <kc6...@gmail.com> wrote:
>
>
> [1] The silly world wrongfully calls that kind of manufacturing method
> 3D printing. It's 3D plotting. I can prove my statement with my

The accepted technical term is “additive manufacturing”. But "3D print" is a popular term that seems to have stuck.

I wonder what terms they use in places like China. Did they borrow the English term?