Rear end musings

[Edmond77]

I used some CAD software I have access to at work to mock up the rear part of my envisioned machine. Based on some older golf carts, it would be leaf-springs only. The solid rear axle would be attached to the springs via bearings. I've used pillow blocks in the CAD but don't have to be. Placement of the motor, sprocket, and brake disc are notional, and I may include a FNR.
With all that said, what will I like and dislike about this setup? Will I need to worry about chain movement during hard bumps? Those who've tried this before, what do I need to know?

Thanks in advance

 

[Functional Artist]

If the "engine" (a motor is powered by electricity) is mounted solid to the frame
...& the axle/sprocket is mounted to the "flexible" leaf springs
...then, yes IMO the chain can & will slack up during suspension travel

It can be set up like this
...but, there is some geometry involved.

The sprocket. on the engine. would have to be the same distance from the axle sprocket
...during the full suspension "travel arc"

 

[Edmond77]

If the "engine" (a motor is powered by electricity) is mounted solid to the frame
...& the axle/sprocket is mounted to the "flexible" leaf springs
...then, yes IMO the chain can & will slack up during suspension travel

It can be set up like this
...but, there is some geometry involved.

The sprocket. on the engine. would have to be the same distance from the axle sprocket
...during the full suspension "travel arc"

Re: engine vs motor. I’m aware of distinction. Fought that battle for a couple decades. Waved the white flag and gave in my baser instincts. My younger engineer-self probably winces.

Re: geometry. good thought. I suppose that could be mitigated slightly by moving axle back or engine forward, making the arc swing smaller relative to separation distance. Alternatively I was considering an idler sprocket, perhaps spring loaded.

 

[MWKarter]

“an idler sprocket, perhaps spring loaded”. Pretty much required in your proposed setup.

 

[ezcome-ezgo]

On my golf cart I made a cradle that was fixed to the axle and the diff housing so the entire thing would move with the axle motion. Worked perfectly.

 

[Edmond77]

On my golf cart I made a cradle that was fixed to the axle and the diff housing so the entire thing would move with the axle motion. Worked perfectly.

Interesting. So the engine was bolted to the cradle too then? Keeping the distance fixed. How was the cradle mounted to the main frame? Bonus points for a photo or sketch

 

[redflash]

I have rear end musings all the time !

Da redflash

 

[Functional Artist]

Here is a "cradle" I built for my Mini_jeep kart

Left motor

...& Right motor

 

[Edmond77]

Nice! And you went with coil overs instead of leaf springs. I was attracted to simplicity of leaves but the cradle/coil is appealing.

 

[Functional Artist]

Nice! And you went with coil overs instead of leaf springs. I was attracted to simplicity of leaves but the cradle/coil is appealing.

Thanks!

I curved the trailing arm
...& call it Faux Leaf Spring

If you're interested, here is the entire build thread (so far)
https://www.diygokarts.com/community/threads/wittle-wesistor-mini-jeep.46893/

 

[panchothedog]

Edmond77. Are you set on leaf springs? Because I am sure you will have LOTS
of problems with the chain loading and unloading if the engine is mounted like in your illustration. I would say you wouldn't go 50' without throwing the chain. Being a mechanical engineer you may find a way around this as suggested in previous posts. But why not KISS. I 'm sure you know what that stands for. A swing arm cradle where the engine as well as the rear axle are both mounted, and move in unison is a proven method used on thousands of
off road karts and mini buggies. No secondary chains, no floating shafts, and no worrying about throwing the chain no matter how big a bump you hit.

 

[Denny]

As an ex golf kart dealer I can tell you the engines are usually mounted to a cradle attached to the rear axle and the cradle is allowed to pivot. E-Z-GO had the best system and best handling karts years ago. One end of the cradle at 1central point mounted to the frame. The other end attached to the rear axle and then housing floaters attached the axle to the springs. If you go with leaf springs you will need some type of housing floater due to the different arc travels of the cradle and leaves. Go coil over to avoid this problem and complication.

 

[Edmond77]

Edmond77. Are you set on leaf springs?

Absolutey not. That’s exactly why I came to the group, to understand what could go wrong znd if this was a fools errand. (It’s also why I’m using CAD software and not a welder yet )

As you said I’m sure I could engineer my way out of it but your point is well taken. There is over engineering and alternatively there is smart thinking.

 

[Edmond77]

As an ex golf kart dealer I can tell you the engines are usually mounted to a cradle attached to the rear axle and the cradle is allowed to pivot. E-Z-GO had the best system and best handling karts years ago. One end of the cradle at 1central point mounted to the frame. The other end attached to the rear axle and then housing floaters attached the axle to the springs. If you go with leaf springs you will need some type of housing floater due to the different arc travels of the cradle and leaves. Go coil over to avoid this problem and complication.

Ahhh. That makes sense. I looked into the floaters and see what you mean. I work in consumer products and not transportation...so much to learn lol

 

[ezcome-ezgo]

This is one of the few photos I have, sort of the proof of concept for me. I used angle iron (!!!) that I had laying around. It is secured to the axle with 2" exhaust u-bolts. There is a homebuilt shaft support, secured same way. Also there is a support bar from the diff to the engine (I think the gas tank mounting bolt). Tried to keep it simple. This photo is from 2014.

 

[Edmond77]

This is one of the few photos I have, sort of the proof of concept for me. I used angle iron (!!!) that I had laying around. It is secured to the axle with 2" exhaust u-bolts. There is a homebuilt shaft support, secured same way. Also there is a support bar from the diff to the engine (I think the gas tank mounting bolt). Tried to keep it simple. This photo is from 2014.

View attachment 136352

Thanks for the ideas. I think I’m being convinced to go swing arm