Downhill Project

[mechanix]

My goal for this build is to have similar geometry to my downhill bike (2007 kona stinky), but have the same power as a small dirtbike. I ride downhill bike a lot and it would be awesome to not have to hike back up after each ride!

Stuff I have purchased so far:

30AH 88V lipo from Hobbycity
4 chargers from Hobbycity
4 meanwell power supplies
2 HXT 80-100 motors with upgraded bearings and re-glued magnets
2 Lyen 12 fet 4110 controllers
Monster T forks
24” downhill rims
4 piston hydraulic brakes

questions
1. Will I have to worry about the tire slipping on rim, is a rim lock necessary?
2. Is there a risk to using regen with two controllers? Both controllers will be connected to the same battery leads (in parallel).
3. Will regular bearings be able to support the swingarm, or should I use needle bearings?

A rough schematic of the drivetrain layout:

Underside view:

Side view:

Top view:

The drivetrain is a fairly simple two-stage with a jackshaft in the middle, which sits on the swingarm axle. On the jackshaft I plan to have a torque limiter and disc brake, as well as the two sprockets.

I'm going to weld the frame out of mild steel because I don't know how to weld anything else. I wish I could make it out of aluminum, or pretty much anything besides mild steel, but that's out of the question unless someone on here would be willing to help me out with that! As it stands right now, the frame and swingarm weight almost 35lbs! I'm still in the design phase, so any comments or suggestions are more than welcome, you won't hurt my feelings!

 

[AussieJester]

Nice design *subscribed ...

KiM

 

[Byte]

Looking forward to this build!

 

[recumpence]

OK, a couple things;

#1 No, I doubt you will ever have rim slippage issues. I have run close to 50hp into a bike wheel/tire without issues.

#2 Your setup should perform to your expectations. My advice is to forget everything you know about downhill bikes and dirtbikes in general and go with what will fit your needs. It looks like you are doing that!

My guess is close to 100 pounds for everything. Of course, you could cut that pretty far by reducing the number of packs you are running. But, that much capacity should give you a full day of riding without a recharge!

Matt

 

[gwhy!]

questions
1. Will I have to worry about the tire slipping on rim, is a rim lock necessary?

sorry Matt, to many variables just to say no about tyre spin.

Simple answer.. Yes. BUT it very much depends on what tire pressure you are running and your gearing, I have minimized this with a couple of daps of silicone rubber on the rim/tire ... do they do a rim lock for cycle wheels ?.


mechanix, Your frame design is very similar to mine and I am to struggling what will be the best way to make the swinarm pivot (bearings or needle ) Im swaying towards bearings with a 14mm axle, But im am planneing on just using 1 smaller motor with a 2 speed gear box.

 

[LI-ghtcycle]

I bet you could use a rim lock from a smaller motorcycle rim (thinking something off of a XR100?) and just drill a second "valve stem hole" and be in business?

 

[recumpence]

questions
1. Will I have to worry about the tire slipping on rim, is a rim lock necessary?

sorry Matt, to many variables just to say no about tyre spin.

Simple answer.. Yes. BUT it very much depends on what tire pressure you are running and your gearing, I have minimized this with a couple of daps of silicone rubber on the rim/tire ... do they do a rim lock for cycle wheels ?.


mechanix, Your frame design is very similar to mine and I am to struggling what will be the best way to make the swinarm pivot (bearings or needle ) Im swaying towards bearings with a 14mm axle, But im am planneing on just using 1 smaller motor with a 2 speed gear box.

Ahh, tire pressure.............. Good point!

I can tell you I, personally, have never had a problem and I have run down as low as 40psi. Anything lower could be a problem. It is good for a trials guy to chime in here because they have more experience with very low tire pressures.

Oh, I know of two mountainbikes running similar setups to yours without tire problems.

Matt

 

[mechanix]

gwhy!, I think I'm going to use a standard ball bearing and see how long it lasts. If it dies, I'm out 5 bucks.. I was trying to source some sealed tapered roller bearings but had no luck. I'm mostly worried about the axial load that they'll see. The reason why I'm worried about the bearings is because when I pedal, it spins the axle for the swingarm. The swingarm axle has to be isolated from everything else in order to not have to pedal every time I apply the throttle... it might make sense with some pictures:

The sprockets for pedal power are directly connected to the axle, and it spins when I pedal. The jackshaft is completely isolated from everything else.

Joel

 

[liveforphysics]

You're very much going to want needle bearings for that double-bearing area. They will both handle the loads better, and take up a small fraction of the space.

vbx bearing

Google it. Those guys are awesome.

 

[mechanix]

liveforphysics, I'm not sure what area you're referring to. There are two bearings seated in the frame, two in the jackshaft, and two in the swingarm. The frame bearings and swingarm bearings will see substantial axial loading, while jackshaft won't see much axial loading. My main issue is trying to deal with the axial loading.

Joel

 

[mechanix]

A few pics of the progress:

It's going a lot slower than I thought, but the design is done, and I started welding it today. The welds are ugly, but they should hold...

Joel

 

[AussieJester]

Welds look fine in the pic, nice work imo... :wink:

KiM

 

[mechanix]

thanks Kim. I forgot to turn the amperage up though when I switch from 16 gauge to 11 gauge, that was a bummer. The whole frame should be welded up sometime tomorrow.

Joel

 

[bzhwindtalker]

I like it! can't wait to see the final product!

 

[mechanix]

Ok, finally had a chance to get some more work done this weekend! The main part of the frame and bottom bracket is done, and I almost finished the swingarm. Once I get the swingarm done I'll be able to paint it and move onto turning out all the pieces for the drivetrain. Here are some pics:

Joel

 

[RWP]

Hi Joel,

Very nice. Planning something similar myself.
If only I could get a welder to look over my shoulder a bit while I learn to TIG. I can braze, buy one of my buddies has pushed me into TIG and so every day I practice a bit but those trained eyes would help a lot.
Can I ask what gauge material you are using? And if several different gauges - where did you choose to go lighter and heavier?

Thanks so much and great work.

Roy

 

[mechanix]

Hi Roy,

I'm in the same boat as you, I would love to get my hands on a tig machine. I'm thinking I might try this same design but with aluminum. I know that they make aluminum welding rods, I'm wondering if it would be feasible to spot weld it together with my stick welder at home, then take it to my school and spend a day on their tig welder to finish it off.

If I remember correctly I used 11 gauge on the top tube, down tube, and swingarm. Everything else was 14 gauge because they weren't the main structural members. looking back, I probably would have used smaller gauges because this sucker is HEAVY. It weights close to 40 lbs with the frame and swingarm combined.

Joel

 

[mechanix]

The frame and swingarm are done, just need to paint them now. I also finished the bottom bracket:

Joel

 

[AussieJester]

Sweet job mate welds look great...

KiM

 

[mechanix]

It's been a good six months since I've been able to work on this project, but I got out of school for the summer last week and I've been making some pretty good progress. I'm not sure if anyone is still following this project or not, but I figured I'd post some pics just in case:


Motor and sprocket setup:

Swingarm:

Charging station:

Motors and batteries:

Charger connecgtors:

The Frame:

Bottom bracket spindle:

Joel

 

[AussieJester]

Thats one solid ass frame, good to see your back working on it all the best

KiM

 

[mechanix]

Thanks, Kim. The frame and swingarm weight about 37 lbs total. I'm shooting for under 150 lbs when I'm done. I could have shaved off 10 pounds or so by going aluminum, but it would cost me an extra $400 or so to buy the stock and get it heat treated.

Joel

 

[mechanix]

Here's a few more pics, progress is slow, but the end is in sight!

I have to machine an adapter for the gator brakes to fit on the monster T forks... it's tons of small tasks like this that makes this project take forever!

 

[Lenk42602]

onward! pretty sure gatorbrake has adapters for post mounts as well as IS. Things like that I wouldn't hesitate to shell out the $$$ for. Time adds up, like you said!

Nice work,

Len

 

[mechanix]

Lenk,

I agree, it would be so worth it to shell out $20 for a bolt-on adapter, but they don't have one unless I upgrade to a 9" rotor. I looked online and the cheapest one was $50! I figured it would take around 3 hours to design and machine an adapter so it's worth my time (my time is fairly cheap these days because I have so much of it).

I have some pics to update:

Cheers!

Joel