RC motor mid-drive plans. Thoughts?

I've been lurking for a few days and appreciate all of the innovation and knowledge in this community.

I've been thinking about electrifying my trail bike (old-school Cannondale Jeykll ), and started working on some plans for it yesterday.

These are the highlights:

• Custom 25:1 gear reduction <3.5lbs
• 2.25kW RC motor
• 44.4v LIPO

I've attached a messy excel spread sheet of basic calculations, estimates, bill of materials, and weights as well as a STEP file (you can use FreeCAD to view) of the unfinished reduction box.

I'd appreciate any thoughts or concerns on this preliminary design.





Calculations and estimates:
https://dustindecker.me/ebikeproject/calcs.xlsx

Reduction box STEP model:
https://dustindecker.me/ebikeproject/reductionR1.STEP

Looks to be an interesting project. are you actually going to make it or is it just more of a design exercise?

one thing i am wondering about with your design- how are you planning on mounting those bearings in the ali plate? do you have access to a mill?

I don't have the money to build at the moment, so just design exercise for now. I really want to build it though. Unless I use very creative (time consuming) fixturing, the housing is a CNC mill job - and I may be able to get access to that.

The bearings will probably be retained by a slight interference fit (with set screw in the housing for popping them back out), or mabey just retaining ring and groove: http://www.mcmaster.com/#retaining-rings/=tuoghs . Thoughts on this?

Awesome!
Did you do the math on the strength of this, at first glance the face width of the gears looks a bit too narrow?
This is pretty much what i have in mind with the same motor, would be pretty darn nice if i could use this design

sevoma said:

I don't have the money to build at the moment, so just design exercise for now. I really want to build it though. Unless I use very creative (time consuming) fixturing, the housing is a CNC mill job - and I may be able to get access to that.

The bearings will probably be retained by a slight interference fit (with set screw in the housing for popping them back out), or mabey just retaining ring and groove: http://www.mcmaster.com/#retaining-rings/=tuoghs . Thoughts on this?

Click to expand...

milling jobs are pricey! wouldnt be crazy for a job like this, but risky seeing as its an un-tested product. when i want to make bearing interfaces on the cheap i just use flanged bearings- you just get the holes waterjet cut at exactly the same size as the bearing OD, and because of the small striations in the cut from the jet it ends up being a good interference fit, sometimes just needs a little polish out.

That's interesting.
I've always wondered if there were some industrial gear unit adapted for the purpose.
I follow you

hello,
Fabio

Moved from E-Bike Technical.

The only concern I have is noise. At the RPM these motors normally run at, straight cut gears will make a lot of noise [even in a housing].

Looks cool, though!

Matt

This might have some similar issues and ideas: http://endless-sphere.com/forums/viewtopic.php?f=28&t=18517&start=550#p416712

Thanks for the link to the Whiplash adventure and saga. Got hooked on the story and read all 700+ posts. Have a incredibly greater appreciation for all the energy and time that goes into taking a seemingly elegant design from the napkin to an actual reliable system.

The rendering is killer... curious what software you are using for that? Before I tried to create a gear reduction from scratch I would try to find something off the shelf that could be adapted. I'm looking at a planetary gear reduction thats off a car starter motor. Starter motor these days are very small compared to what they once were. Partly because they are now permanent magnet type motor and have planetary gear reduction as well. But gears require lube and a much cleaner environment than a belt drive. Hard to beat the simplicity of the HTD belt reduction drive. I PM'd recumpence about buying some of his pulleys but he has yet to respond. So I've found a supplier in China making some for me... so hopefully soon will have a cheaper alternative for folks wanting to roll their own belt reduction drive.

yawstick said:

The rendering is killer... curious what software you are using for that? Before I tried to create a gear reduction from scratch I would try to find something off the shelf that could be adapted. I'm looking at a planetary gear reduction thats off a car starter motor. Starter motor these days are very small compared to what they once were. Partly because they are now permanent magnet type motor and have planetary gear reduction as well. But gears require lube and a much cleaner environment than a belt drive. Hard to beat the simplicity of the HTD belt reduction drive. I PM'd recumpence about buying some of his pulleys but he has yet to respond. So I've found a supplier in China making some for me... so hopefully soon will have a cheaper alternative for folks wanting to roll their own belt reduction drive.

Click to expand...

Hey, Man. So sorry about the PM. I recently formed a corporation with a partner and we have been moving everything over to a new Web site for all correspondence. Your PM got lost in the shuffle.......

Matt

I apologize for not replying for a while, life has been getting busy.


schmuijel: I didn't do the any strength calculations on the initial model. I made it parametric though, so I just change a few values it the file and everything updates (distances, gears, housing, etc). I will do stress and fatigue estimates and publish them when I have the time. It is likely that the package will increase in size.

madm3chanic: I have mill access, possibly CNC. By flanged bearing, do you mean something like this?:

I haven't seen those before. I'll keep them in mind. I suppose it could be used for a design using two plates held together with rods like this toy: ] The sides would have to be covered up to keep out debris and keep lube in but it might be a possibility for fabrication without a CNC mill.

fab0: I've looked for a commercial unit with the right form factor, no 90-deg bends, right size, right reduction, and not very expensive without luck. The market is open for someone.

recumpence: That's a very good point, spur gears can get pretty loud under load at high RPM. Mabey I should look around for some helical gears for the first stage. They would be more expensive and require thrust bearings though.

spinningmagnets: Thanks for that link, it is almost an identical project. It seems he has abandoned it due to noise of the gears and outrunner. The housing I am working on will be sealed and have an oil bath with the possibility of helical gears on the first stage so it should be significantly quieter. The motor noise would still be an issue though.


yawstick: The views are screenshots from Solidworks, with Real View and Ambient Occlusion enabled. Renderings using Photoview would really be killer. I'll look at starter motor planetary gearing, I did not consider those. Off-the-shelf is certainly preferred!