DougM's latest build - Sand Runner

[DougM]

So it’s raining in Seattle - we had a lovely week or two earlier in the month but now the rain is back which means all the activities I had planned (esk8ing mostly but a bit of bicycling) got cancelled and that means time to work on the Runner!

Both transmissions complete, broken in greased and ready to roll:

Now because I’m using aluminum extrusion as the frame for my board I need to make 2@ 21 degree truck mounts. I’ve made these before, but I screwed up the first one this time around (I had an embarrassing hack of a holding system for the mill involving an angled piece of plastic, It was really janky and the piece jumped out of the vice in mid cut) I decided to do the right thing and mount them properly this time and rotate the vice 21 degrees instead of trying to mount the part 21 degrees into the straight vice. This is what I came up with

And here are the finished pieces

The slots allow me to embed the mount into the extrusion (there’ll be a picture of this later and you’ll see what I mean)

Here’s a picture of my daily driver esk8 so you can kind of see how it all goes together:

So I just happened to have a frame from an old thane build that I scrapped so I went ahead and started mounting stuff to it just to see how it would fit. That’s when I noticed my mistake.

so far so good…

Now that’s looking downright sexy.

You can’t see it in the picture, but the truck is backwards. I didn’t consider when I was modelling the profile that the truck had a front and a back (which it really doesn’t except for the logo and the bolt head/tail) and I had a 50/50 chance of getting it right, which means, inevitably, I got it wrong.

But I don’t think I really care. Obviously the truck is linear so functionally it makes no difference and I can mount the front truck correctly (the one people will see) so I’m letting this go.

Next steps:

1. I need to make a decision on the tires - do I continue to wait for the other two plastic wheels to arrive or do I bite the bullet and start designing/3D printing hubs for the rubber tires. I’m leaning towards rubber.

2. the old frame in the above pictures isn’t long enough. I need for the rails that form the deck to be at least 37" and those in the picture are probably closer to 29 or 30, so a Misumi order is up soon.

3. I’m debating on the deck. I was going to make a bamboo and walnut deck, but unfortunately I found an old maple ply deck that’s pretty close to the correct length and already shaped and ready to go, so despite the fact that the bamboo deck would be a work of art, practicality dictates that I use the one I have. I can always swap it out later.

Lastly I decided not to get the Maytech motors because despite what they say they are clearly not IP54, as evidenced by this still I grabbed off the advertising video:

you can see the coils between the can and the face, which means sand would get in there and destroy it in a matter of minutes.

[sesat]

did you find a motor that was legit sealed that you could use?

[DougM]

Nope, I’m going to have to build housings around the Aerodrives

[ZachTetra]

Maybe one of the waterproof hydrofoil motors?

[DougM]

Those are all inrunners and they start at $500.

Keep the ideas coming, though!

[ZachTetra]

How will you enclose the motors? Just a printed press fit or a aluminum can that bolts to the gear box or someting?

[sesat]

they make 6013-2rs bearings. 100mm outer diameter, 65mm inner diameter. i wonder if it could be used with a 3d printed sleeve to seal a motor

[RyEnd]

3-3.5-4 (10") ag tires.
https://www.alibaba.com/product-detail/10inch-3-00-4-3-50_60713389205.html?spm=a2700.galleryofferlist.0.0.2b2e30320IbFkJ

SSS inrunners have tons of power. You can find 56xxx and 70xxx 10kw motors for <$200. Introducing more problems to solve like high kv and super long housings, but both are addressable.

[moon]

These teeth look tiny. I wonder how they will fare.

[ZachTetra]

I think the wheel is just absolutely massive in comparison

[DougM]

ZachTetra:

How will you enclose the motors? Just a printed press fit or a aluminum can that bolts to the gear box or someting?

I was going to 3D print shells for each motor that have some sort of fabric on the end to keep the sand out but allow some air circulation. I have mount holes in the rear plate for this, but I haven’t designed them yet.

I’m debating on attaching a small fan blade to the back end of the motor to encourage air movement, but then I have to have an outlet on the other end, which isn’t hard, but probably will take a couple of iterations to get it all together.

[DougM]

moon

These teeth look tiny. I wonder how they will fare.

They are pretty small (and smaller as that was a prottype gear that I actually cut to the wrong depth)

The gear is 1/2" wide and Acetal is amazing stuff, so it should be ok.

The problem, though, is that my gear cutter has a bit of vibration in the cutting head, so the gaps are slightly wider than the teeth are, so the gears aren’t perfect, but beaches are flat, so the actual torque load is quite small.

I’m probably over-motored with 6374’s.

[DougM]

RyEndSkateshred ambassador

3-3.5-4 (10") ag tires.
https://www.alibaba.com/product-detail/10inch-3-00-4-3-50_60713389205.html?spm=a2700.galleryofferlist.0.0.2b2e30320IbFkJ

A loose sand runnier is a totally different thing, and these tires would be great for that. I encourage somebody to build one! You’d need 4WD and tons of battery. The thing would have to be a real beast but sooooooo fun.

[DougM]

So this is the story of what should have been virtually nothing. I thought it would be easy to make rims but it turned out to be incredibly difficult and after several nights last week and this entire weekend I still haven’t made 1 rim.

Saturday Morning:

From the left, what you’re basically looking at is the inner aluminum plate, the inner rim, the gearbox portion of the interface, the bearings and their mount blocks, the outer aluminum plate, the outer rim, the center aluminum plate and the rim portion of the interface.

I’ll talk about the interface later.

These things were all cut or printed late last week and were ready to be assembled Saturday morning

The first thing I noticed in the cold light of morning was that there was absolutely no reason to have the center aluminum plate. I think originally I had planned on threading it and screwing into it, but at some point that plan went aside because the threaded-aluminum-rod-as-spacer is much easier and much stronger.

Then almost all of the bearing mount blocks became obsolete because I realized I could integrate the bearings directly into the wheel interface and the inner rim directly, as shown here

BEFORE

AFTER

Now, I don’t have any pets, and my shop is only accessible via my back yard, which is completely fenced in. Yet somehow this dog managed to not only find her way into the back yard, she invited herself right into the shop and started barking at me, presumably of the same opinion that my original design needed work.

Here are some more pictures, just because a thousand words and I know you guys aren’t here for the words.

So after spending most of the day Saturday making improvements I came up with the following.

Wait.

I promised I was going to talk about the interface.

So the problem with all machines is misalignment. In our case the alignment between the transmission and the rim is going to be pretty close, but not perfect. If you tie the two directly together you’ll either get a whole lot of vibration, you’ll break something or eventually you’ll destroy the bearings.

So this is where I totally get my MacGuyver cred because this idea is completely wacko, but it actually works. Caveat this wasn’t my idea, but I’ve used it a time or two.

1/4" irrigation hose.

Yep. the kind you get at Home Depot to spray the plants in your greenhouse.

Your inner and outer interface plates have 1/4" holes around the outside rim. Enough to handle the available torque. I chose 7 because there’s 7 mount screws (actually there’s 14) so symmetry. Here’s the interface at the transmission

And then you just leave the slightest gap between the two interface plates:

And the hose will handle any misalignment issues. You can also use 1/4" solid rubber tube, but it’s surprisingly expensive and I had a mile of this stuff in the greenhouse.

At this point one of the interface plates is on the 3D printer and the latest revision of the outer rim is on the other 3D printer, so those will be in a future post, but here is how the newest and latest version of the rim goes together

Note that the inner plate and outer plate are aluminum. They are the plates that the tire bead will actually be pushing out against. The screws that hold the outer plate on will go all the way through the outer rim and screw into the inner rim, putting the outer plate and outer rim in compression, and the screws on the other side will screw through the wheel interface and the inner plate putting those in compression.

So aside from shattering there is no way this rim could fail (bwah hah hah hah!) I can’t believe I actually said that.

[Andy87]

If you still searching for motors you could have a look at the maytech 6880. they have a big from bearing which means it’s more sealed than the sealed 6374 motors.

[DougM]

Bad news and Good news. The bad news is my 10 hour print job augured in

And then my printer died - wouldn’t boot anymore.

The good news is my old printer, which is a lot less finicky, still works, so I was able to print the outer rim in a beautiful shade of midnight

Aaaaaaaaand we have a fully assembled wheel!

The problem is I don’t have screws long enough to attach the outer rim - 2 1/2", so those are on order.

And after a few hours of putzing I managed to get the first printer back online, so now I have everything I need to make 3 more sets.

It’s time to start thinking about batteries already.

[DougM]

@Andy87 I’d love to take 2 of those 6880 motors and make a mountain board with front and rear differentials and full suspension

Mountainboards using regular trucks are just too grueling both on the rider and on the components.

[DougM]

4 wheels, 4 sets of parts in process…

[DougM]

Quick update. I planned to have a rolling chassis by the end of the weekend, I had all the parts for all 4 wheel assemblies

But fate is a cruel mistress and had other plans for me. Ok, a bit overdramatic. I had a flat tire.

I tried patching it but my patches are shite, so I ordered some new tubes.

So instead I’ll be working on the electronics housing.

Also, I made a kind of a stupid mistake,

I was going to use the screw mounts to mount the housings around the outrunners to keep the sand out, but as you can see I perfectly aligned the wires with one of the screws. So I’ll either need to design the housing to not use that screw (easy and will probably work fine) or, well, I don’t have any other option.

Though I was reading another build and the builder (@glyphiks) mentioned that he had bought some sealed Maytech 6374’s so I pinged him to see if he thought they really are sealed.

Edit: @glyphiks got back to me, the motors are not sealed.

[aletheuo]

@DougM

Your inner and outer interface plates have 1/4" holes around the outside rim. Enough to handle the available torque. I chose 7 because there’s 7 mount screws (actually there’s 14) so symmetry. Here’s the interface at the transmission

You made a giubo!

I never would have thought to use that in an eskate application, so I applaud the ingenuity.

I don’t have anything productive to add, but as someone who has also made chips, your ‘not-a-machinist’ skills are way beyond my level. Hats off to you