First Build - Featherweight Bar Spinner

[Wkdintent]

I bought the Turnigy 9x TX as well. Just making sure you know that as is, it won't failsafe. I had to fit an FrSky module with one of their Rx's. I also flashed the Tx, not sure if that was necessary but the software is a lot better.

[Dr. Crane]

Great, thanks everyone for the help!

I will get a request off this week to sort the pulleys out.

In the meantime I have ordered one of the housed bearings which I am using on the drive shafts and the weapon shaft so that I can actually get a look at it. I’ve only actually modelled it from the spec sheets thus far and they are a little bit ambiguous with some of the measurements (to me anyway). The hope is that I will come up with an idea to simplify the bulkheads as they will currently require quite a lot of cuts - hence the large CNC estimate.

[Dr. Crane]

I have a few questions and would be grateful for any help.

1. Is it okay for the pulleys to overhang the motor shafts as long as the grub screws make contact?
2. Are keyways absolutely essential or will grub screws generally hold up okay?

Thanks!

[Ocracoke]

To answer your questions directly:

1. Ish. My axe motor does this on my middleweight I think but not by very much. I would prefer the pinion gear to be wholly on the axe motor itself since I don't really want to end up bending the shaft.

2. In my experience, no, not on a drive train but keyways do help lock in a gear or a wheel hub onto a shaft. The axe motor I have on my middleweight has a small keyway which I drilled a specific point to allow the grub screw to sit in. Depends on how much force is likely to go through it. In the lighter (i.e. Beetlweight) classes, I don't bother with this and simply screw the grub screw onto a flat on the motor shaft.

[Dr. Crane]

Hello - hope everyone enjoyed the holidays!

Thanks to the kind advice above, I have bought new Gimson motors as suggested. In order to accommodate these larger, heavier motors my design is now larger across all three dimensions.

This then presented a weight problem and so I have designed some cuts in the chassis to try and save weight - I'm estimating the chassis to weigh in around the 4.5kg mark (based on a 2.71g/cm^3 density).

The good news is I now have access to a makeshift and somewhat limited workshop but it does mean I can do some of the machining myself.

I have a few more questions and would, as always, be really grateful for any advice:

1.I currently have one 5S 4000mah 30-40C LiPo - is this going to be enough to power the drive and the weapon or am I going to need two?
2. From my attachment "Overview" v2 - I have never worked with aluminium and so I am wondering if parts of the chassis are likely to bend under force given I have now cut weight-saving holes?
3. From my attachment "Motor Bracket" - I am wondering how I can drill these horizontal holes into the bracket? I am also looking to thread them. It is 1/2 inch thick (note in my CAD the holes go all the way through just for ease but I'm only expecting to drill enough to bolt it to the bulkheads).

Thanks once again and a Happy New Year to everyone when it comes!

Cheers

[Dr. Crane]

Hello all,

I’ve made a few changes to the design - mainly reducing the thickness of the chassis from 1/2” to 3/8” or even 1/4” where I think it will allow.

The aluminium has arrived! I spent an hour making the attached cut The marked section is one of the bulkheads.

This is the only remaining 1/2” section though so that’s as hard as the blade will have to work. They aren’t super fancy blades so I imagine I might go through a few but will see how it goes.

Ive sent off a piece of 3/8” sheet to be cut by waterjet - this is for the V shaped arms at the front which are now much simplified. The shop is miles away and only open Mon-Fri so will be a while before I can pick them up! Lots to do before I need them anyway...

Plan is to get the bulkheads cut and then start drilling holes for attaching the drive motors. I have a cheapy pillar drill which I am hoping will prove to be good value!

As im at the startup phase - the biggest expense seems to be buying lots of little bits like drill bits, saw blades, files, lubricant etc. - all adds up!

I’ll get some more cutting done this week(end).

cheers,

P.S. does this thread need to be moved to Build Diaries? Can a mod do that or do I need to start a new thread?

[James Williams]

Looks like this thread is coming along well. I can certainly sympathize with being a newcomer & having the tools drain the budget! Don't worry about the thread, it's fine here.

[McMullet]

Good going! Cutting 1/2" ally on a table saw looks scary.

Has the design changed much with the move to home-building? I find my designs for robots feature a lot of rectangles, since I have to cut them myself, whereas stuff I design for work gets sent to a machine shop so it's all fillets and funny angles.

[Dr. Crane]

Good going! Cutting 1/2" ally on a table saw looks scary.

Has the design changed much with the move to home-building? I find my designs for robots feature a lot of rectangles, since I have to cut them myself, whereas stuff I design for work gets sent to a machine shop so it's all fillets and funny angles.

haha I’m actually surprised at how well it’s done considering it’s a £20 blade!

It was a fairly simple design to begin with, but I have made it even more simple since I got some equipment to cut it myself.

The main worry now is there are some large-ish holes to cut (up to 56mm diameter) that I’m not sure how I’m going to cut.

thanks for the feedback!

[Eidg]

Perhaps you could use a hole saw?

[Dr. Crane]

Perhaps you could use a hole saw?

I was thinking this but it’s 1/2” ally and not sure how good (expensive) a saw would be required!

[McMullet]

I've cut through some thinner aluminium with a cheap hole saw. Took a while but worked fine and the saw managed OK. I think I did 3 pieces of 4mm thick sheet which is 1/2" total. That was only a 20 mm hole saw though. The other problem would be accuracy, you probably won't find a 56 mm hole saw and if you do it will probably cut 59 mm holes...

I guess ideally you would want to use a milling machine and a boring bar to cut a hole that size, if you can get access to one.

[Dr. Crane]

So the blade gave up on me before I could cut out one 120x210 bulkhead! it came in a pack of two (40/80 teeth) so will put the new one on and see how it goes!

Ive also realised cutting straight lines even on a table saw is a little bit difficult but maybe that’s just me!

I therefore bought a file yesterday so when I’m done cutting I can take the last few mm off. Is this viable with aluminium? I know it’s a soft metal but can I realistically take say 5mm off an edge without breaking an arm?

im hoping this is super difficult mainly due to the thickness of the metal! As I said I’ve got 3/8” and 1/4” for the rest of the parts so it should get a bit easier lol

cheers

[team death]

You would do better to invest in an small angle grinder if you are cutting

metal out and a variety of blades for slitting/grinding.

The thing about alluminium is that because its so soft , five minutes with a

file and the file gets clogged and you spend more time cleaning it

than filling-better to use a flap disk in a grinder.

[Dr. Crane]

You would do better to invest in an small angle grinder if you are cutting

metal out and a variety of blades for slitting/grinding.

The thing about alluminium is that because its so soft , five minutes with a

file and the file gets clogged and you spend more time cleaning it

than filling-better to use a flap disk in a grinder.

thanks very much for the tip. I’ll take a look at some cheap grinders tomorrow.