DougM's latest build - Sand Runner

[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

[aardelandings]

Hi, enjoying this thread.

i think your tyre choice is going to cause you problems, firstly they are going to fling sand everywhere and that will become annoying very quickly, also they are only 2ply and you stand a good chance of ripping them to pieces.
Can i recommend looking at slick tyres that are used on mini moto bikes and quads. Will fling a lot less shit and stand up to the abuse. Trade off is that they are a bit heavier.

[DougM]

@aardelandings good call on the tires. They were my second choice because half of (2 of the 4 I ordered) my first choice got lost in the mail. However, the good news is that the vendor (China of course) has sent out 2 new ones, so I will continue to use these wheels/tires for development and hopefully for test runs, but when all 4 of the other ones are in I’ll switch.

Of course this means I’ll have to completely redesign and re-manufacture the rims. Ugh.

[DougM]

Ok, so despite some setbacks my goal this weekend was to have a rolling chassis and here it is!!!

If you look closely at the deck you’ll see it has 2 sets of screw holes - it is recycled from an earlier board, so I’ll have to fill the empty holes at some point. Or not.

The setbacks were that I removed a feature from the outer rim and in doing so I didn’t notice that the air valve opening (which was dependent) got removed, so I printed the part first in black, then more of the midnight blue came in so I printed it again - all the time not noticing that there was no hole for the tube valve.

So 5 hours later a new print of the part.

The new tubes came in and hold air, so we are fully rolly.

Next up I went to order batteries. I’ve been buying these Lishen’s from LiIon wholesale because they are super cheap and high capacity, but only 12A (which is actually perfect for this project since beaches are flat I’ll never need more than 60A) But they are out of stock.

Amazingly these Molicels are only slightly more expensive, higher capacity and a whopping 45A, so I immediately ordered a set. However, they are too nice for this board - I want to transplant them into my daily driver.

Back story, I ride with a friend, and since I DIY and he off the shelf’s I can usually easily out power and/or out distance him just by making subtle upgrades to my board. However, his last board is both a better hill climber and has more range than my board (his is thanes, mine is 6" pneumies). I was going to let this go because I don’t really care (I might care about the range thing, but we’re only talking a couple of miles - mine does 20, his probably does 22) but with the above Molicel’s I could dominate once again!

So now I have a much more complicated project because I have to transplant the Molicels into the old board and then take the old cells and put them in the new board. Normally this would be easy, just swap the pack across, but I mount each P pack to the rails, and the ralis are different widths between this board and the Daily Driver. So it’s much more complicated than it should be.

I’ll keep you apprised as to how this goes.

Next up the electronics box and I am working on a no-spot-welding implementation of the battery pack, so I’ll outline more details in a subsequent post.

[DougM]

I’m not sure what the consensus here as to what constitutes Dead Sexy, but I can’t imagine this doesn’t come close

Yes these are Molicel 4200mAH 45A 2170’s

Over the winter I was trying to figure out ways to put together a battery pack without welding, and I came up with gold contacts on PCB’s with a sort of a rack mount.

This is sort of partially assembled - the black plastic wings will bolt (the holes aren’t there yet) to the aluminum extruded frame of the board under the deck.

As it turns out not all 2170’s are the same diameter, the Molicels are 0.839 vs the LIshens which are 0.851. Not a huge difference but enough that I need to make some adjustments to the plastic carrier before I make more of them.

I hope to have all the packs made by the end of the weekend but, as I said, these won’t be going in the Sand Runner, they will get transplanted into my Daily Driver and that pack will get moved over to the Sand Runner.

Getting all that done by the end of the weekend will probably not happen, but I’ll keep you apprised.

[moon]

Those cells are 30a btw

According to mooch at least

[DougM]

Well, I got totally off target this weekend. I posted a week or so ago about my belt slipping on my Daily Driver and the end result of that was when I converted it from chain drive to belt drive I got the wrong belts. I got HTD 3M where I needed HTD 5M.

So that meant replacing both the motor pulleys, the wheel pulleys and the belts. the Daily Driver runs 6-shooters and I had been complaining about the fact that I didn’t quite have enough hill climbing power and slightly too much top speed, so this was an opportunity to change my ratio a bit. I wanted to go to 4.4:1 from what I have now which is 4:1, but running 3M belts. With the new battery pack going in I’ll be able to bump up the battery current too - probably an additional 10A will do the trick

So I needed a 66T and a 15T. The 15 wasn’t a problem, you can get those at any esk8 shop, but without spending a horrendous amount of money you can’t get a 66T. So I had to make one.

Now I’ve made chain cogs before, but I’d not made pulleys. Turns out they are almost exactly the same. I grabbed a CAD file for a 60T off SDP-SI and modified it a bit to make it 66T, then I had to order a special cutter because all the ones I had that were a usable diameter weren’t long enough to cut the depth I needed.

Then the Delrin that I had in stock turned out to be 3/8" and not 1/2" as I thought it was, so I had to make each one twice (which actually works out better since I need to be thicker than 15mm, which is ~0.59"

Anyway, here it all is:

The grey things are what was originally going to be the edges of the pulley when I thought my Delrin was 1/2", they would extend the thickness just a little bit, like this:

but I won’t use them.

The 4 in the center are the 66T’s and the two on the right are 15T’s. I figured I’d make a few for testing since once you have the tooth profile it’s easy to make them in any size you want, you just have to math out what the OD of the pulley is and then attach the right number of teeth to it.

Here’s a picture of the mill cutting the 15T’s

Now I wait for the belts

I did get a little bit of work on the control box (electronics housing). When I have that baked I’ll talk a lot more about it.

[DougM]

@moon

Those cells are 30a btw

According to mooch at least

You mean I can only put 150A at the wheels? I’ll be lucky to survive the week

[ZachTetra]

Why not just get the right belt instead of new pulleys? I’m pretty sure belts are cheap and easier

[DougM]

@ZachTetra

Why not just get the right belt instead of new pulleys?

Belts and pulleys are matched - 3M belts work with 3M pulleys and 5M belts only work with 5M pulleys.

This is the profile of a 5M

[DougM]

Battery packs are all built up and control box, aside from the top, is basically complete.

A couple of detail shots on the control box. As you can see it’s all 3D printed and segmented. This way I can change the input and output configuration just by printing new grey pieces in the format I want.

It’s turned out to be a pretty good design, I used it on the Daily Driver and I’ll likely retrofit the Mountain Board with it if I ever find myself cracking it open for an upgrade.

Next is a lot of work. I need to disassemble the Daily Driver, remove the battery pack, install and wire this battery pack and then reconfigure the Daily Driver’s original pack for use in the Sand Runner.

In a perfect world I’d like to have the Daily back on the road both with new batteries and new 5M pulleys and belts before the long weekend. Unfortunately the new belts don’t arrive until Tuesday, so that’s pretty tight.

[Plurf]

The control box is pretty cool, great 3D printing skills out there

[DougM]

Ok, the Daily Driver’s upgrade to 5M pulleys and belts is complete The pulley turned out unusually wide.

So now I can get back to what I’m supposed to be doing. I made a nice carbon fiber cover for the control box

I know what you want to ask - Doug, how do you cut carbon fiber? Well, you use a tile saw blade, you wear a decent air filter and you have a lot of air movement - like a big fan running while you cut it so the dust doesn’t get into your lungs.

You can drill it with a standard drill bit.

this is the carbon fiber I used

I’ll probably work up some slightly better looking screws…

Next up is the battery pack. I’m going to wait a week because I don’t want to cannibalize the Daily Driver right before a really sunny week, but next weekend I’ll swap the PCB pack into the DD and start to figure out how to retrofit that pack into the Sand Runner. I don’t have enough plastic in stock to make the brackets anyway, so I guess tomorrow will be a non project day.

[Redeye]

Can you speak to, and show better pictures of, how you secured the bullet connectors to the 3D printed part? Following, excellent work!