Dog walkers either stop for a chat or give me dirty looks. No in between!
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Experiencing some motor problems…
You can see here, the motor closest to me turns without any abnormal resistance. The other motor has an arc of about 120deg where it feels significantly different and struggles to go the full way around.
This morning, I was thrown off the board but luckily it was low speed (approx 10-15mph) and managed to run it out instead of falling. I thought I had just hit a pothole or something but I’m wondering if this was why. It also sounds very rough and “growly” as opposed to a consistent whine.
When I get home I’ll take the belt off and see if I’ve just got too much tension on the pulley but I doubt thats a concern because I can still easily depress/deform the belt myself.
Any ideas?
Are your phase wires all in good condition?
Otherwise it could mean opening up the motors and checking there’s nothing weird going on.
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Turns out it was nothing to worry about. As soon as I took the belts off they ran without any problems. Further inspection and I noticed the 16T pulley was clogged with mud and grass. That, plus the fact that my belt tension was pulling the motor mount slighlty out of alignment because of my bodge job clamps was causing the issue.
Stripped down the deck over the weekend. Fuck me, butyl tape was an absolute bitch to remove but I wanted to confirm everything was as water tight as I had expected because I had rode in some rain the other day. Dry as a bone thankfully. Now I need to get some more butyl to re seal everything but in the meantime I’ve used some self amalgamating rubber tape as a half decent substitute for a gasket.
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Today’s stats:
Had a concerning moment when I turned the remote off when wheeling my board into a shop to grab some snacks on my way into work. Just after the remote turned off, the board started full throttling in reverse up a hill and almost hit some guys shins. Luckily it stopped moments before disaster. I have no idea what happened there, maybe I caught the throttle before turning it off, but hopefully it doesn’t go off on a mind of its own again 
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TIL You really can’t trust Strava!
I’m going to assume I was around 35-40mph top speed which is a new record for me. I definitely felt faster than I’ve been before.
I think this calls for an investment into some telemetry at some point in the near future.
Anyway, recorded battery stats today.
26 mins on the charger before I left the house brought the battery from 41.9V to 43.2V. Depreciated to 41.4V by the time I got to my destination. I ought to charge it for at least an hour every day I ride to maintain a consistent charge.
@Venom121212 kindly sent over some stickers for my enclosure and they look awesome! Especially a fan of the riptide tramp stamp 
When they arrived yesterday I was at work. My Fiancée was a bit confused…
On a slighlty soppy note, I’m really grateful for this community and all the support I have received in this build. You guys are so helpful without expecting any return, and it’s really exciting to be a part of such a fast growing sport/engineering advancements.
I’m already planning my next build. Super keen to try making a onewheel and at some point an MTB. But I’ve got a busy year ahead - finishing my degree and buying a house (and setting up a workshop in the garden!) take precedence. Plus, before all else I need to get my 3D printers back up and running and I’d like to build a CNC mini mill (mostly to make esk8 parts…)
So new new builds for the foreseeable future. In the meantime, enjoy your weekly doeses of Nagini content.
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badgerbadgerbadger
a sssnnaaaaake aaa snaaaake!
Nailed it.
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Didnt get many opportunities over the last week to ride Nagini or do any work, other than a quick trip to b&q on Saturday to get some parts to fit new washing machine.
This morning’s stats:
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Shit, you ok?
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Yeah, anticipate a small bruise tomorrow but nothing major. Was slowing down at the time so it was okay just took me by surprise!
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Took Nagini for a spin this morning. Went all the way to one end of the busway and back with a detour through the chalk hills.
Battery before ride:
Strava:
Battery post ride:
Took some footage on the way back. If you fancy hearing my rambling nonsense commentary and dog walker conversations, as well as watch me fail to stand on the board and dodge bushes, here are some links:
Oh also here’s a cool video
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Had a pretty chill evening ride with Nagini. I think this was my longest ride yet but sadly I have no stats to show because my phone was on low charge.
Popped round to Tesco and picked up some 300lumen flashlights which I ziptied to the front of the board. Worked perfectly as a bodge job, just need to 3D print a proper mount…
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Is that a rail line for… buses? 
Yep! Its called a busway. Not many of them about but its great.
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Couldn’t sleep last night so I decided to put the time to use and figure out how to improve my motor mounts.
Let’s start from the top. Following multiple revisions based on all of your feedback last year, this was the design I settled on to fit the Caliber III stock profile:
This design seemed pretty solid as a first prototype but it has become apparent there are many issues which need to be addressed.
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Internal sharp corners which are impossible to machine. These had to be converted to small radii during machining which prevents the hanger profile from making full contact with the flat faces.
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There isn’t enough space to get a socket around the nut. I desperately tried and went through about three sockets. The hole was originally threaded but that didn’t last long. A spanner around the nut works, but only when the clamp and arm are disassembled. Once the arm is assembled, it is impossible to make any adjustment to the mount position.
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The relief cut isn’t deep enough to facilitate enough deformation when the clamping screw is tightened.
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Even if it did deform as much as expected, it would cause the two flat faces closest to the opening to create a taper as opposed to converging flat against the hanger profile.
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Caliber III hangers are cast. This means they have a very imprecise profile tolerance. On top of the poor clamping force, internal fillets and tool deflection from my friend’s old decrepit CNC, this clamp stood no chance of holding up to any sort of vibration. After my first 5-10 mins on the board, it fell off. This is what led me to buy a set of BN 220’s.
I was under the assumption that the clamps would fit BN hangers better due to the extra precision. At the time I thought it was just the cast profile which was the problem, but alas I was wrong so I ended up “reworking” it…
On one of the clamps, I drilled, counterbored and tapped a hole then screwed in an M4 socket head screw and loctited it in place. Unfortunately the tightening torque sheared the bolt in half, so now the mount is held on by a couple of threads and some threadlock. That’s not exactly confidence inspiring when you’re going 30mph.
On the other clamp, I got distracted while drilling the counterbore and accidentally went through to the internal pocket. I tried to drill a new hole in a different location but the drill bit snapped inside the clamp and I couldn’t get it out. I went through almost every drill bit I own, trying to remove the stuck bit but had no luck whatsoeber. I didn’t have the right size tap and/or screws to work with the larger hole so I made do by gluing in an M6 screw and capping both ends with epoxy putty. I did warn you, it’s not pretty.
So yeah, my motor mount situation is sort of fucked right now. But I’ve rode about 50 miles or so on this frankenstein’s monster of a drivetrain without any major dramas. However in the last week or so, I’m noticing the mounts are becoming a tad wobbly. That spurred me to stop putting off the redesign and get to work.
I came up with this design which I was confident in getting machined and using for the next prototype:
This version has all of the right fillets and clearances to enable the flat faces to interfwce parallel to the hanger. But after revisiting the design last night, I’m still not happy with this solution for one reason.
In theory if the clamp is tightened to the trucks first and then the arm is fastened onto the clamp, the index hole positions will have moved due to the clamping deformation and therefore produces a risk of stripped threads and difficult assembly. If instead the clamp is tightened once the arm is in place, we still have the issue of not being able to put a socket or spanner in the space and therefore it will be difficult to apply enough clamping force for a secure connection.
Other motor mount designs overcome this in a number of different ways:
Mboards and a few others use a 2 part clamp. I’m not a fan of this as it would severely limit the amount of rotational adjustment, plus the arm is only secured on one side of the mount which could be a risk for heavier motors.
Another common solution is slotted holes. These may take up some the deformation from clamping, but by relying on friction for the rotational constraint on the arm there is a high risk of the fastners vibrating loose.
Using some kind of toothed/notched system where the arm slots over the clamp and is somehow constrained axially could work, but would create a tradeoff between the resolution of rotational adjustment and the risk of the notches slipping. This is because the valleys between each tooth would need to be filleted, and with the smallest possible tool diameter, the smaller the distance between each tooth/notch, the closer to the tip of the tooth the fillet gets.
The grub screw clamping method is hated by many for good reason, it’s shit. It doesn’t provide enough contact between the clamping faces and the hanger, is prone to loosening via vibration, and leaves ugly marks.
So here is the solution I’ve come up with. I’m probably not the first to try this, but in my research I haven’t seen anything similar.
It’s pretty self explanatory. The tool clearance has been carefully considered to ensure the primary clamping surfaces aren’t compromised. There is a spring washer under the head of an M6 bolt to help protect against vibration. Paired with some loctite, I’m confident this will be more than sufficient.
My only concern is stripping the aluminum thread. However unlike the previous clamping method, the load through the threads will be perfectly aligned with the holes. Maybe a helicoil would work?
I’m considering adding a small spring washer inside the “insert” piece instead of under the cap head to serve the additional purpose of creating additional tension between the screw and insert to support the clamping force generated by tightening the screw.
Anywyay I’d love to get some feedback on this. Has anyone tried anything similar? If so, how did it go? Are there any glaring issues that I’ve missed?
5 Likes
Motor mount redesign is a work in progress. There are a few issues with the arm that needed addressing too, such as it not being long enough (with the motor in low tension position, the pulley rubs against the tyres) and due to the large wheel pulley, I only ever have 5 teeth in mesh and there is a risk of slippage under harsh acceleration/deceleration.
Here is some CAD porn:
As you can see I’ve also added a slot for the motor shaft to make assembly/disassembly easier, and rotated the tension slots by 45 degrees. To solve the slippage issue, I’m adding holes for idlers using 605ZZ bearings. I was hoping to use standard skateboard bearings but it just wasn’t working out.
The scope of this is growing immensely. I also want to add a crossbar which doubles as a carry handle AND light bar. I’m also considering designing some printed covers to reduce the risk of debris getting under the belts and/or damaging the motors.
I spent a few hours trying to find a solution for the crossbar that was aesthetically pleasing, didn’t add too much length to the already extended mount, didn’t waste a huge amount of material in machining and would be robust. I’m a bit stumped, even after looking at other people’s motor mounts I just wasn’t satisfied so I’m going to give my brain a break and instead I’ve been working on some flashlight mounts:
I’ve also made all of my designs fully parametric, so when I’m finished I will share the f3d files and if you’re interested in making your own it should be easy enough to adapt. To demonstrate…
Some of my CAD isn’t the most robust so…if you break it, don’t say I didn’t warn you!
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