DougM's latest build - Sand Runner

[DougM]

So the other weekend I took the mountain board out on the beach here in Washington state (Long Beach if you happen to be local). The nice thing about this beach is that cars are allowed to drive on it, so nobody even notices if you’re racing up the beach on a skateboard (actually a lot of people noticed, but in a good way)

The downside to the mountainboard is the motors are not sealed, it’s chain drive and the wheels are 8" but way too skinny to be of much use in sand. It worked, but it took a lot of battery to keep going. Also, by the time I got done riding it was starting to sound funny, so we’ll see how much damage I did

Anyway, it was enough fun that I’m going to build a task specific board - a sand runner (caveat, wet sand). It will need to have large diameter wide but lightweight wheels, sealed gearboxes and some sort of covers for the motors. Basically the whole thing has to be sand-proofed.

This is currently in the planning stages, but I have started to assemble some parts.

MBS Trucks
Ali Express Kayak carrier wheels

I’ll be running 10S5P of 4k Ah 2170’s and, unfortunately due to budgetary constraints (and because you can’t get FOCBox Unity’s anymore) will be running some old VESC 4.12’s driving 6374’s that I have kicking around.

This is going to be physically a much longer board than your usual longboard - I’m thinking 4 1/2 feet long. The trucks are 16" wide so should piece together pretty nicely.

First up, building my own gearbox (since I can’t afford the eToxx). This thread will start with that and since this is my first build on this forum I’ll talk a little bit about the frame and batteries later.

[rafaelinmissouri]

Have you seen the guys with four wheels in the back?

[DougM]

Here’s how it all started - I wanted to see if my Mountain Board would work on the beach. It’s got 8" pneumies, so I wasn’t expecting much, but it worked surprisingly well so long as you stayed in the wet sand. I got good vibes from other folks on the beach and I ran all the way to the end (this is on the Oregon Coast) of the beach.

The only problem was that occasionally right in the middle of the wet sand you’d hit a dry spot and either you’d launch right off the front of the board or you’d almost launch.

The problem was the tire contact patch area just wasn’t big enough. You can see from the picture just how deep the tires were digging in. It worked but it took too much battery to go the distance.

The other problem is that this board has standard 6374’s on the back and it’s chain drive - 2 things that definitely aren’t sand friendly.

[DougM]

@rafaelinmissouri, I thought about putting dualies on but they’re still only 8" and it’s heavier and more complicated than I wanted, but thanks for the link/ideas!

[sesat]

welcome to esk8 news! glad to see you made it over here

[Venom121212]

Check out the mbs fivestars. You can put 9" tires on them and even 10" but they bulge a bit over the wall. Very light as well. Always wanted to tear up a beach!

[BillGordon]

Good to see you here. Matched your level from .builders.

Nice build and welcome to the other side!

[DougM]

Thanks Bill!

[malJohann]

Holy adjustable wheelbase Batman!

[DougM]

Apologies for this thread being a little disjointed - I started it on another forum but decided to move it here. So there will be some repeats and duplication along the way until I get to new material.

This was, about a week or so ago, the beginning of the gearbox design. I had very little information on the specific parts I was going to use, I just had the gear ratio (20:125) and the motor (6374) so I started with those.

I chose 20 for the drive gear, even though it’s a bit big, because I happened to have cut some 20T brass gears a while ago, and they turned out so nice I have to use them for something

I know what you’re asking, how did I cut the gears? Well, for a project a long time ago I built my own gear-cutter. At the time I thought I was going to have a side hustle building little gearboxes but it turned out gearboxes are a lot harder to build than you’d think so it never went anywhere.

But I dug the machine out and cleaned it up, fixed a few things and spent a lot of time trying to figure out what I was thinking when I built it and then I fired it up and cut a sample of the 125 gear. I also 3D printed the housing so here they all are. (I stuck a pen in there so you could get an idea of size. The actual gearbox will not include the pen)

That’s about it for now. Oh! one more thing. I was putzing around in the carport and I found a set of 4 10" tires! These aren’t the ones I’m going to use for the final machine, but for prototyping they’ll work just fine.

I say that but if the wheels that come in from China are total crap these probably will be the final wheels.

Next time I’ll talk more about the design of the transmission and call out some specific parts that I have coming in. Like the MBS Trucks, which are already here; and the bearings, which are not.

[sesat]

this is going to be awesome!!!

[alexnz]

On sand, I found that it makes a MASSIVE difference to have pretty soft tyres. When used with a kite, it’s maybe not that critical because of some weight being carried by the vertical lift of the kite, and also there is some significant side load that the tyres have to be able to handle, so there needs to still be a fair bit of pressure. But when used with a wing or a sail, and I imagine with electric propulsion, softer tyres make all the difference in terms of getting stuck or making it through softer patches. I tend to carry a small bike pump with me so I can adjust to the conditions.

[kubbur]

What tires are you going to be using, they might do good in the snow here

[DougM]

@kubbur I was going to use these Kayak carrier wheels but @alexnz is right - you want rubber underinflated for maximum contact patch. If you’ve ever watched any youtube videos about 4WD in sand those guys run around 8 to 10 PSI.

The downside to underinflated rubber is that you will eat your battery really quickly. So I’ll try both. We’ll see which one goes better. I’m confident that for sand either will work and both will have upsides and downsides.

Snow is a different matter - with sand so long as its wet it’s pretty consistent, but with snow it sometimes is icy and sometimes you just fall right through the stuff. I don’t think wheels will work at all. If I were serious about an E-snowskate I’d probably do some sort of small half-track on the back and those short little mini skis that were a thing a few years ago in the front.

[kubbur]

Thing is that there is usually snow on the sidewalks but when crossing intersections there is no snow there, e-bikes don’t really have a problem with this because of the large wheels, perhaps it would suffice to put 9" mudpluggers in the front too and deinflate them to some low level, daily commute is around 8km*2 so I could charge in between if I need to, would have to pull 40wh/km to have to charge though

[Venom121212]

Do you think slicks would do any better or worse in sand? All the beach buggies I see use slicks but they’re also being pulled not pushed.

[DougM]

@kubbur no matter what you do make them as big as possible. I wouldn’t go below 10"

@Venom121212 re: slicks - it doesn’t matter in terms of going or stopping - wet stand will grip anything, but it matters a lot in terms of carving - if you have slicks you will slide out which could be fun if you grew up snowboarding. I don’t know whether the plastic wheels with the ridges will do better than the rubber tires, it’ll be fun to find out

[DougM]

So tonight I finished up the gearbox. I still don’t have the motor mount designed yet, but here are some pretty pictures from the virtual world

Now I need to get all the parts into the real world. That will require making the inner and outer plates and I won’t have time for that until this weekend.

In the meantime I spent some quality time reading through the 3D printing subject and I think I’m going to attempt to make rims for those 10" tires out of PETG. My read is that it’s almost as good as nylon, but a lot less fussier to print. So between now and this weekend I’ll be doing some initial wheel designs.

Oh, back up a second. I wanted to mention - if you look at the above pictures the parts that are kind of brownish are the bearings. Those are these: Inner and Outer.

Interestingly on these trucks the ID of the inner bearing is different than the ID of the outer bearing. I actually had both the correct inner and outer bearings in stock but the inners (ID = 0.5", OD = 1.25") I only had shielded and not sealed, which sand will destroy in seconds. So I had to order 4 of the sealed variety.

[TheMrLarin]

Great work man! Watching with interest!

[DougM]

Parts are starting to arrive, the aluminum for the inner and outer plates and the PETG is here, so I can start thinking about wheels. Since I’m “of a certain age” I’m thinking they should look like this:

The prototype of the driven gear is complete

I’m hoping the bearings get here by the weekend so I can put the prototype together and see if there are any surprises. After that I need to order the Acetal for the production gears. Since it’s not cheap I only want to do it once and not screw it up.

I’ve been thinking about swappable battery packs. I’m not sure whether I’m going to try to get a design together this time around because I really want this board done when the CV quarantine is lifted and in WA state that’s probably not much past June 1. But since this will be my 3rd board and I only ride one at a time it makes sense to have a single or maybe 2 battery packs I can swap into the board I want to ride rather than sinking a lot of money into a permanent pack for each board. Esp since they lose capacity with age regardless of whether you use them or not.