What gearbox? Turboshaft engine

[noshell]

Hi All
Progress on my turboshaft engine has been very slow as i am now a father

But it is still progressing, here is my current engine, it runs nice and the turbine wheel does not glow red. My plan is to use this hot housing from a bigger turbo as the freepower unit. The area of the freepower turbine is about twice the area of the engine turbine so i think it should be an okay match.
The only gearbox i can think of using is an angle grinder gearbox. I think a custom gearbox with a pinion and two spur gears either side would be optimal as there would be no axial or transverse load on the shaft, it would probably be very loud though.
Ideally i want a gearbox from something that already exists. An angle grinder is good for 30k rpm with a bit of ol grease inside, and thats with tons of shock loading. I rekon it would be good for 50k rpm with an actual oil supply.
Any ideas for gearboxes or comments on using a turbo hot housing as a freepower?


ibb.co/r6swvSj

[richardm]

You may want to look at this
www.ebay.ca/itm/223370403754?hash=item3401e9dfaa:g:pX4AAOSwCjpcWk3f&amdata=enc%3AAQAIAAAAwFM8mEo942sMBPCHSGKUctGGtdMTwcB3dkNuLGMoU1bgs%2BYI6aFpDme3Lnirh%2BnL4bDXOxqsYc0UpNpuzbaW4DNFjSpUcmCXvnHZuwcFzVK%2Bak4914RD8QLOEIcsr35q5YlzSpAcc7LC%2FzJUg1nK6FrTFb7GwSmTMmrUNpP%2BBPLEpylDN11Wj6Vjn%2BPFWV36fgvpg25NoFTm3gOpJkLthHOEOOBpUoW6JXkiyp9hllD1SXtDUrYW7lsFyjL9WOM5yQ%3D%3D%7Ctkp%3ABk9SR9qToJGsYw

[racket]

The truck unit with its freepower wheel would be even better , just need a bit of interconnecting plumbing

[noshell]

I have seen those before. I think its a little bit too big for what i want, though i appreciate the comment.
The end goal is to mate it up to a 125cc scooter cvt and power a bike with it.

So far, the angle grinder gearbox is the best i can come up with.



I know some kart chains and sprockets can do 20k rpm. But i would like more. That turbo housing is probably dreadfully inefficient at that speed

[richardm]

Yes it may be too big and too heavy for your project. Angle grinders are available in different sizes. From 4 1/2 to 9 inches or more. It may be worth looking at the speed and gear ratio of different sizes and makes.
Generally the larger grinders turn slower but I dont know if their motor s are spinning as fast as their smaller counterpart
Obviously a large one is sturdier and handles more torque .

[wannabebuilderuk]

Feb 1, 2024 7:58:03 GMT -5 richardm said:

Yes it may be too big and too heavy for your project. Angle grinders are available in different sizes. From 4 1/2 to 9 inches or more. It may be worth looking at the speed and gear ratio of different sizes and makes.
Generally the larger grinders turn slower but I dont know if their motor s are spinning as fast as their smaller counterpart
Obviously a large one is sturdier and handles more torque .

9" seem to spin at 6-8k rpm and have a rough 4:1 ratio so motor will be going at 24k for 6k which means they definitely could be used as the motor is often 2kw.

www.etotheipiplusone.net/?p=3128

[noshell]

I feel like it would just about work. No shock loading and a proper oil supply, i might get 10kw and 50k rpm if im lucky.

As i say its the best i can come up with. Other ideas welcome.

I think rotrex superchargers use some kind of gearless system. They use rollers instead.
Its a nice idea but Id imagine anything i can turn on my lathe will just disintegrate at 50k rpm

[richardm]

When you say 50 k rpm are you talking about the input or output shaft? And 10 kw seems a lot to me for a grinder gear box....Thats about 13 hp on a device designed for 2 hp at the most

[noshell]

50k input from the freepower turbine. I think thats the most i could expect anything to handle.

50k max turbine speed, then say 5 to 1 reduction to the crank of a scooter engine would be 10k rpm which seems reasonable.

[richardm]

Yes Reasonable with oil lube on the bearings. But Im still questioning the 10 kw power handling of an angle grinder Seem a lot to me

[enginewhisperer]

I have been looking for something similar, hoping to put a turboshaft setup into a motorcycle too.

I actually have a Detroit DD15 freepower turbine unit but it has been sitting in storage in the USA for a few years. I need to work out how to ship it to Aus for a reasonable price!
They are very heavy though, and it's probably not easy to make it much lighter.

I have a few Segway gearboxes, which are around 24:1 reduction and have very high quality gears in them.
For my purposes I'm thinking I'll convert one to single stage (the second stage is 5.35:1), to bring my 40+krpm turbine speed down to something that will work with a chain drive to the rear wheel.
I'll try to get an extra large rear sprocket for at least a 4:1 reduction on the chain.

[noshell]

Yeah, its not ideal Richard.
Ill look into the segway gears.

I also found out some old Seadoo jetskis had centrifugal superchargers, but the gearset is elusive.

[monty]

Probably best to copy a supercharger drive. Something like paxton. They just use spur gears. You don't want to mess with helical. The uneven tooth loading and thrust loads can cause serous issues with high rpm gearsets. Most of the big turboshaft engines PT6 etc use straight cut gears, and a planetary gearset. Unfortunately this is a rather arcane area of gear design, and most of the guides and textbooks consider it "impossible". Gears must be precision ground or lapped. Pinion may need a modified addendum, and a subsequent adjustment of the main gear center/center distance.

Here is a good source of stock gears.

I've used QTC for many years for all kinds of projects. Take a look at some of their integral shaft pinions. Already hardened and ground with bearing mounting pre-machined. You won't have issues with shock loading or bending, it will be surface durability that gives you problems. Use oil spray between the mesh for cooling. Turbine oil or one of the new light weight automotive oils.

You probably want something around module 1 gear size.

Monty

[richardm]

I think you' re right about spur gears A bit noisier but who cares. But still the problem now turns to the housing... Making a precision housing and machining the bearings holders with precise gear center to center and clearance is something of an undertaking. I think its better to find a suitable complete gear box.

Most commercial turbines use spur gear in their accessories gear box. ( The PT- 6 does too but has helical gears in its main gearbox)

[monty]

Helicals are fine if you really know what you are doing, but not worth it for us, at least in my opinion.

I don't see making the gearbox that big of a challenge. Not compared to finding one that will work for such a obscure purpose. All you need is a decent mill with a DRO and a little know how. Line boring the case, lapping or honing solves all the alignment issues. Use some decent deep groove hybrid ceramic ball bearings and you should be good. It just depends on what your capabilities are.