XO-1 spur-to-pinion adapter that includes the "Cush Drive"?
 

Hi guys,

Maybe I'm going a bit overboard here, but I was wondering if you guys think it would be possible to make a spur-to-pinion adapter for XO-1 spurs by mimicking the alloy part of the "Cush Drive" as the mounting part for the motor shaft. If that alloy part (think it's called the "Cush Drive Key", Traxxas part no. 6465) would be replaced by a custom CNC-ed part that can be fixed to the (8 or 6 mm) motor shaft with a set-screw, then the whole Cush Drive function would even be intact, which sounds great to me for running with a center spool. Possible concern might be the thickness of that gear mount assembly though -whether that would fit on standard 20mm shaft lengths- and possibly the weight.

Reason I ask is I'm looking for ~50T size mod 1 pinions. I know they exist in steel, but I think they might get too heavy. Also, I want to see if I can avoid steel-to-steel gearing; given the pinion will be paired with a much smaller 34T spur, I think it makes most sense to have the pinion (biggest) in plastic/composite/delrin and the spur (smallest) in steel, or even both non-steel.

Any thoughts?

If anyone that has access to XO-1 parts could post the thickness (and weight?) of the of the spur-mount assembly, I would be very grateful.

EDIT:
Could it be as simple as just tapping a set screw hole in the cush drive key :D? Does anyone know the diameter of the center hole of the key?

http://www.traxxasmodels.co.nz/images/6465.jpg

http://www.dollarhobbyz.com/media/ca...spur_gears.jpg

Sounds like a good idea and should be possible. I can slide the Cushdrive right over the shaft of the Turnigy motor :)

Hole is 6mm and I would say there is enough material to bore it out to 8mm if needed.
Pin diameter is 2.5mm. Width of the whole assembly is 21mm, but the bearing seat on one side could be cut-off, then it would be 16mm.

Cushdrive assembly (without shaft) with 46t spur is 28g.
For comparison:
35t Kershaw 5mm spur is 52g.
34t XO-1 spur is 36g.
Aluminum spur adaptor with 36t Revo 3.3 plastic spur is 14g.

Thanks for the detailed response Lizard! Much appreciated and very helpful, hurray for the 6 mm shaft :). Ordered 2 sets and going to see how it works out. Looks like I need to do some reading on how to tap threads with no tools :D.

Does anyone have any thoughts on running plastic-on-plastic gearing? Or better go with plastic-on-steel?

Cool. Do you have the Kyosho already? Looking forward to see a thread about it :)

Yes, figured I deserved an early Christmas present:

http://www.rctech.net/forum/members/...photo-1-94.jpg

http://www.rctech.net/forum/members/...photo-3-75.jpg

Proper powerplant mock-up:

http://www.rctech.net/forum/members/...photo-3-74.jpg

Gearing options:

http://www.rctech.net/forum/members/...t2-gearing.jpg

Will put together a thread soon :).

Still work in progress, but thought I'd throw in some pics to show feasibility.

http://www.rctech.net/forum/members/...photo-1-98.jpg

http://www.rctech.net/forum/members/...photo-2-99.jpg

http://www.rctech.net/forum/members/...4-photo-51.jpg

Sorry, I have nothing nice to say :)

The CFK plate will act as a heat insulator, the motormount also seems to be optimized for worst possible heat transfer ;)

I think you could achieve way better heat transfer to the chassis with an aluminum plate and a motormount that has a larger area touching the chassis.

IMHO it's unecessary thick for onroad use, wasn't it made from 7075 T6?
Better would be 2mm (or something like that) thinner, but with the whole length touching the chassis and an additional screw to the chassis on the motor side.

No problem Lizard, your feedback and insights are greatly appreciated. And you are right :). I will just have to compensate with some big-ass fans :).

The motor-mount is basically a 1717 mount design, customized on my request to fit a 56 mm can. I did not explicitly take heat-transfer into account in the requirements I set, so I don't blame the maker. Ideally, I would have liked to see a bit more material covering the front endbell too, but this is how it came out. The fact it's so thick does mean it has a little more thermal capacity by itself.

The CF plate is not part of the motor mount design, but my own creation; it was necessary because I overlooked the clearance required for the rear endbell screws... Opted for a spacer instead of cutting another slot in the chassis for the screw, so I could also close up the chassis holes around the gears (they annoy me and I want to see if I can run all plastic gears, so I need to keep stones out as much as possible). An aluminium spacer is a good idea, might make one later.

I am really curious how the Turnigy motor will hold up at such high gearing, and I'm a bit worried about cogging. Did you try out yours already?

Couldn't motivate myself to work on the XO-1 yet and still need to order a new rear axle carrier for it. I guess it will be next year until I try it out.

What spur to pinion adapter did you get?

I hope the plastic/plastic combo holds up. Perfekt solution then IMHO. Very lightweight, no diff, but still some 'give' because of the cushdrive. And cheap compared to Kershaw pinions if you need to try out different combinations.

Regarding the endbell screw: You could use a set screw with blue threadlock. Would be flush with the can then and should hold up. At least that's how my TP5670 came.

That's a great idea, thanks! Actually feel a bit stupid for overlooking that... and I was so proud of my heat-insulating-motor-mount-spacer-creation :lol:.

The spool adapter for mounting the Traxxas spurs on the 6 mm Nitro tranny shafts is made by the same guy that did the motor mount and battery tray (don't want to be rude towards Mike, so I won't link to them here - I started a preliminary build thread with some more info at the other place).

The idea of tapping a set-screw hole in the cushdrive key is a bit on hold right now. The thing appears to be made of steel, there is just so little material and contact surface (4.5-5mm) compared to a normal pinion (6-9mm) - see pic, and I don't even have a drill-press (yet), let alone the skills to tap a tiny 2-2.5 mm thread in such a small steel thing. So as a plan B, I ordered a bunch of XO-1 29T and 34T pinions (super cheap at amain with their $2 intl shipping :)) and I'm going to try and dremel a pinion into the shape of the key, so I get a cushdrive key with a regular stable pinion base and set-screw. If successful, I'll grind down the shaft to 5 mm.

http://www.rctech.net/forum/members/...0-photo-52.jpg

Dremeling a spur until it looks like the drive-key? That's ambitious :)
Where will the base fit then? I think there is no space inside the spur assembly (?)

Maybe make a CAD drawing and have it made by some CNC service. An M3 screw in a 4.5mm wide drive-key should be no big problem I think. The hole would have to be 2.5mm, that leaves a mm on each side. Even M4 could be okay considering that the drive key is 5mm wide near the center. 3.3mm hole would leave 0.6mm at each side at the top and 0.85mm near to the center. But that would probably require good material (not brittle and also not soft). Or use M3.5, but screws and taps are hard to find for those.

Or maybe go to a local machine shop or something and have them drill a hole into the motorshaft so that you can use the pin to mount it.

Haha, yeah, sounds more like it has disaster written all over it... you're right, I think I should just drop by a Kfz Werkstatt here to see if someone can tap a M3 hole in it. Comparing the contact area to a regular pinion, together with the small set-screw, just doesn't give me a very comfortable feeling yet, and I'm worried it'll be too wobbly, given the shaft won't reach the hole in the 2nd plastic end-cap.

I'll keep the CNC service in mind, thanks, didn't even know those existed. As another backup plan for if the whole Cushdrive plan fails, I ordered the OFN40760 Center Gear Mount. It has a 8 mm bore, so needs a reducer (or 6 pole TP motor :)), but Ofna has 44T-49T plastic spurs to go with it, so it should still be nice, light and cheap. Also have a $10 30T 6mm bore pinion (steel, 82g...) on the way from aliexpress, which I could use as a spur on the GT2 tranny shaft. Increases gearing options a bit: 49/30 (max Ofna) gearing would yield 112 mph no-load and 54/30 (max Cushdrive) 124 mph - no idea whether the motor will like that though.

Also haven't decided yet on ESC. Still attracted to XL2 to keep the door to 8S open at later point.

http://cdnll.rcplanet.com/images/l/OFN40760.jpg

Finally tried preparing the Traxxas XO-1 cushdrive key for use as spur-to-pinion adapter, but wasn't very successful...

With a lot of effort I managed to drill a 2.5 mm hole in it (HSSE Cobalt drill), but then it cracked when I tried tapping the M3 thread (at about 1/3rd in). The material is extremely hard and it took very long to drill the hole, maybe because of that the hole needed to be a bit bigger diameter for the thread to be tapped?

http://www.rctech.net/forum/members/...photo-1-12.jpg

http://www.rctech.net/forum/members/...photo-2-12.jpg

From what I know, 2.5mm is the right holesize for an M3 thread.

Is the tap high quality? If it took a high quality drill to make a hole, maybe the Traxxas material is just too hard and/or brittle?

You could try some very high quality taps (those with 3 different ones that have to be used after another) but that's gonna be expensive and probably not worth it given the uncertain outcome.

Crap. Sorry that it didnt work out.

You definitely need a tap specifically for hardened materials, but the hardened cast parts generally don't respond well to re-machining operations. You may have some luck if you cheat a little on the drill size(stuff is hard, so it won't likely pull the thread even if you drill a little bigger). Carbide tools and lots of lube!

That stuff is tough as nails; Kudo's for you to take the plunge to try it. J

The problem is that the tap isn't meant for these hard materials; it literally pushed the part apart, rather than cutting it away. Without a special tap, i would cut a 2.7mm hole for tapping. (requires less force to cut the thread) The threads will be less deep, but considering the hardness of the material you don't need to worry. I sometimes use an oversized drill for the tap in aluminum that's less 'willing' to be tapped. With tough materials I use cheap (conrad, lithium) grease instead of oil for cutting.

It would be fair easy to make a motoradapter for that spur from aluminum, loosing the cushion. (it would probably mean less wobbling as well)

Hi guys, thanks for the feedback!

I don't know much of metals, but the grainy texture inside means it's sintered I think. Best bet is probably drawing up the part I want and having it made by a CNC service, like Lizard suggested earlier.Do you guys have a recommendation for a good CAD tool for someone without prior CAD experience? Sketchup any good?

@Serum, I would actually like the idea of the cushdrive to have some drivetrain cushening, but you might be right that it will cause wobble. Maybe I just have to settle with the tire-surface contact as the only cushening :).

As long I haven't gotten the XO-1 cushdrive spurs to work, I will be using the OFNA DM-1 spur mount. Those spurs go up to 49T. Later I found the OFNA GTP spurs go up to 51T, but they use a different mounting system. For now I think I'm good with the 49T as that allows gearing between ~150-180 kph nominal no-load with the gears I have, and I'm not sure if the batteries and motor can do much more anyway for continuous use and whether I find enough space to actually use those kind of speeds.

@Lizard, did you try the motor yet in your XO-1?

http://www.rctech.net/forum/members/...on-adapter.jpg

http://www.rctech.net/forum/members/...photo-2-15.jpg

For the benefit of anyone reading along, here's the OFNA part no. of the alternatives. Both spur mounts have 8 mm bore, so need a reducer for 6 mm motor shafts, like I used in pic above:

http://www.rctech.net/forum/members/...dm-1-spool.jpg

http://www.rctech.net/forum/members/...ofna-33020.jpg

But now you're limited to a 49t pinion,do you still want to go with the 54t in the long run?

Yes, you are right; it is sintered material. For CAD, i use solidworks. don't know enough about sketchup..

Thanks, I'll look into Solidworks.

I don't really think 54T is necessary anymore. The need for the big pinion is very specific for the low RPM (900kv, 6S max) of this motor and I could still go a bit down on the spur, to loads that are probably way beyond what the motor will be happy with. I just thought it would be cool to have the cushdrive thing.

Below's an updated gearing matrix, listing no-load wheel-speed (in kph) at nominal Voltage. I need at least 39 mm shaft-to-shaft distance or the motor will rub the rear chassis brace, so red cells are out of the question.

I already have the Aliexpress 30T 6 mm bore pinion, but it's just a huge and clumsy chunk of steel, weighing a whopping 87 g, which is a bit more than I like (complete spool with 36T plastic gear only weighs 56 g). I might also try and bore out a 29T XO-1 pinion I have laying around, material is the same as the cushdrive key, so at least I know what I'm getting myself into :). Kershaw also has some 8 mm bore pinions that would work on the spool shaft with a bore reducer, but he charges $20 intl. shipping even on that small stuff, so that would mean a $40 pinion, which I would like to avoid.

http://www.rctech.net/forum/members/...gearing-v3.jpg

http://www.rctech.net/forum/members/...4-photo-10.jpg

http://www.rctech.net/forum/members/...08-photo-5.jpg

When you're new to solidworks, just go through the tutorials. It works miracles.

Don't worry too much about the weight. it's aerodynamics that's your concern at these speeds. The weight of the pinion won't affect your topspeed; it's neglectable in regards to the drivetrain/drag.

If you can't accelerate with slipping wheels, it might be an indication that your 2 kg heavy pinion is too much :)

If you want, you can ship it to me, and i can cut of the largest chunk of that useless collar..

Liquidrc can ship to Europe for ,97 usd, and has the TKR4190 in stock. But that's 5mm again. (though it might be easier to drill than the hardened Traxxas pinion)

Yeah, I just want to make it as easy on the powerplant as can be, main goal is to have a fast car that can finish a pack without overheating. But you're right, in total the weight of that pinion plus spool shaft will be in the order of a normal center diff with steel gears.

Thanks for the offer! I appreciate that and will keep it in mind. I had some good experiences with LiquidRC before, always good prices and fast shipping to EU.

Cheers!