Where can I buy metric titanium screws

[kelemvor]

I just looked at the shear strength for the titanium screws. It seems Titanium is not the answer. I got it in my mind that titanium was stronger, but after reading I've found that apparently that only applies for the same weight of metal. When volume is the same, steel has the higher shear strength although it's heavier. Weight is a factor but for 28 tiny screws it's kind of an insignificant difference. I should have looked that up first, but at least I caught it before using them.

 

[Couv]

I just looked at the shear strength for the titanium screws. It seems Titanium is not the answer. I got it in my mind that titanium was stronger, but after reading I've found that apparently that only applies for the same weight of metal. When volume is the same, steel has the higher shear strength although it's heavier. Weight is a factor but for 28 tiny screws it's kind of an insignificant difference. I should have looked that up first, but at least I caught it before using them.

Well, are you going to tell us what you're working on? Inquiring minds want to know.

 

[Diving Dubai]

Screws - Titanium - Alloys - Teknipart Ltd

Stainless Steel - Alloys - Teknipart Ltd

Obvs UK but they're a professional specialist fastener supplier and you can buy online

 

[BoundForElsewhere]

I just looked at the shear strength for the titanium screws. It seems Titanium is not the answer. I got it in my mind that titanium was stronger, but after reading I've found that apparently that only applies for the same weight of metal. When volume is the same, steel has the higher shear strength although it's heavier. Weight is a factor but for 28 tiny screws it's kind of an insignificant difference. I should have looked that up first, but at least I caught it before using them.

I was going to mention that. Good thing you figured it out. About 20 years ago NYC rebuilt the wood boardwalk at Coney Island using titanium wood screws. Every year more and more are headless.

 

[kelemvor]

Well, are you going to tell us what you're working on? Inquiring minds want to know.

Nothing amazing. Autonomous drone that can lift about 23 lbs. The battery should give me about 45 minutes flight time and will consume 5.7lbs of that lift capacity. Fight control computer is an STM32H743 (arm cortex m7 @480mhz). dual 1w 900mhz transceivers should give me a little over 6 miles of range. I'm thinking of mounting my nikon dslr on it for the main video but haven't really given the video solution a lot of thought yet. It runs the Ardupilot RTOS. Motors will draw about 2.1kw at 100%. I'm a little worried about the power, 30amps at 24v per motor is kind of intimidating. Those motors will produce a metric buttload of torque (that's a technical term) hence my concern about the fasteners for the motor mount and propeller mount. Other users of the motor have complained about shearing fasteners, and I'd really like to avoid having something stupid like that fail.

Yes, there are better designed motors available with similar (or even greater) power. However, these bad boys are only $50 per motor and the next step up is to a motor that's $300 per. It needs 4, and if the thing works out I may switch it over to a hex in the fall so I have some redundancy in the drivetrain. The better motors just cost way too much. So.. I'm left trying to solve the mounting problem.

Some folks tackle the problem by drilling additional holes, add glue/epoxy/etc. I was thinking of tackling it by simply using better hardware. I don't like the idea of drilling into a precision BLDC motor.

 

[saxman242]

Other users of the motor have complained about shearing fasteners, and I'd really like to avoid having something stupid like that fail.

A lighter weight fastening solution would be to use a pair of steel shear pins and then lightweight fasteners from there in loose fit holes for each motor. Or design your mounting interface to include the shear features.

 

[michael-fisch]

I'm glad you guys understand it, cause I sure don't. Just thinking about bending and clamping 3/0 wire to the batteries and controller scares me a little bit.
From the controller to each motor you can use really thin 10AWG wire.
Over what weight does a drone have to registered as an aircraft?
Here in Germany I had to keep my model planes under 5Kg for many years.

Michael

 

[letterboy]

The multiple attachment points would lower the stress on each fastener.

But at a certain point you have to have some point of failure in a system, no?

If the mounting hardware is stronger, what is the mount/frame made from?

Would a stronger screw cause the frame on the motor to become mangled under load?

I am sure you have gone through this thought process.

Adding more fasteners in the way of additional screws that are drilled and tapped may not be the worst idea. You could theoretically add 2 screws to each motor and reduce the stress by half on each, no? Or am I doing bad math...

 

[saxman242]

The multiple attachment points would lower the stress on each fastener.

If we're talking about shear loading on the fasteners, it's not actually possible to load up more than 2 fasteners at the same time (unless you're match drilling countersunk fasteners). You can distribute clamp up over multiple fasteners and handle some of your shear through friction, however, if we're talking pure shear loading, it's just the 2.

That's where putting the Ti fasteners into a clearance hole to make sure they're definitely not the ones taking shear and using two high strength shear pins to handle that loading makes the most sense. Or just do it with the motor mount geometry.

 

[letterboy]

If we're talking about shear loading on the fasteners, it's not actually possible to load up more than 2 fasteners at the same time (unless you're match drilling countersunk fasteners). You can distribute clamp up over multiple fasteners and handle some of your shear through friction, however, if we're talking pure shear loading, it's just the 2.

That's where putting the Ti fasteners into a clearance hole to make sure they're definitely not the ones taking shear and using two high strength shear pins to handle that loading makes the most sense. Or just do it with the motor mount geometry.

In my minds design the motor is mounted underneath a piece of material and the screw is counter sunk into that material. To be honest that was just for pretty looks...

but all of this is null depending on the material the motor is mounted to. He could use the strongest fastener, but if he is mounting through a 3d printed plastic part it won't matter much (over time). . .