scorpion fx

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goatman   10 kW

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scorpion fx

Post by goatman » Nov 11 2019 9:20pm

I picked up a fairly used scorpion fx with rear suspension. problem, the rear triangle is for 20 inch tires. I need to get a rear triangle or swing arm for 26 inch tires. has anyone does this yet?

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Re: scorpion fx

Post by amberwolf » Nov 11 2019 10:22pm

Unless you also change the front by the same 3 inches or so, changing the rear like that will greatly change the geometry, which will change it's handling (usually negatively, but you'd have to try it in different situations to find out how bad it actually is).


One way to use bigger wheels is to build extension plates to bolt to the dropouts; it's been done for hubmotors and regular wheels on various builds, but it does create a potential weakness at that bolt-on point depending on how you do it, because it adds a lever arm against that point. Haven't heard of any failures of anybody's mod yet.

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Re: scorpion fx

Post by Dauntless » Nov 11 2019 10:23pm

Not to disagree with what he's saying but since they do make the configuration you want it might go without problem.

My first thought is you should figure out if the Scorpion 2 swingarm will fit. Picture won't prove it does but you might be more or less confident after a look. I'd say if you're plucky enough you should be able to find something that will work.

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goatman   10 kW

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Re: scorpion fx

Post by goatman » Nov 11 2019 11:04pm

yes I understand the geometry problem but I think a lot of the issue might be solved by the length of shock/spring with a ground clearance loss although come to think of it if the frame isn't fairly straightlined you could lose the motor push in the spring. another issue might be the path the chain takes but its not really going to be a pedalling trike. ive seen that scorpion fs 26 but I really don't want to know their sticker shock price for that part. ill just buy a cheap bike on craigslist and grab my sawzall and bolt something together, atleast ill have a starting point for what needs changing

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Re: scorpion fx

Post by amberwolf » Nov 11 2019 11:22pm

Hopefully there will be no problems, but if you want to know ahead of time if the smaller rear can be converted to the larger, you could ask the company if the two trike versions use the same frame, or if they have different angles for the steerer tubes on each frame.

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Re: scorpion fx

Post by goatman » Nov 12 2019 12:05am

I went to hp velotechnik website but I didn't find a parts department. I don't have to cut the trike it is 4 3/8 inches where the swingarm attaches/pivots. I don't want to use extensions because I made extension plates for my bob yak trailer and that was a pain because of levering and basically those plates got pinned to my frame and 2 torque arms were needed for regen braking with my trailer on. my axle torque actually opened the 1/4 inch stainless v3 torque arm. theres a lot of forces happening right there. I should start posting some pictures in the build section

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Re: scorpion fx

Post by goatman » Nov 18 2019 8:24pm

I emailed hp velotechnik and they said you cant upgrade the scorpion fx to a 26 inch swing arm without it oversteering in corners and you would have a tough time keeping it straight. I ordered a mxus 3005rc, 20 inch rim, spokes and a phaserunner from grin. hopefully I can pick it up Thursday and be riding Saturday.

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Re: scorpion fx

Post by Dauntless » Nov 18 2019 10:13pm

Oversteer? They're expecting that you'd shift a lot of weight backward? I think the guy might just be guessing. The faster you're going the more serious oversteer would be, but my understanding of tadpoles is they tend to understeer, so this would be quite a reversal. He might be thinking that it would raise the rear with the taller tire, I don't want to venture a guess at what might lower it some to make up for that without seeing it all. But I don't know where it turns into overkill on something small like a tadpole.
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Re: scorpion fx

Post by SlowCo » Nov 19 2019 8:02am

Why do you need to go from 20"to 26"?

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Re: scorpion fx

Post by goatman » Nov 19 2019 8:45am

slowco, the 20 inch tire is really slow if youre pedalling, also my other bike is a 24x3.0 kenda flame tire on a 3540 motor. I wanted to use that motor with a duro wildfire 24x3.0 tire for winter to see how the trike handles with that setup.
dauntless, I was thinking the same, my rear pivot was 7 inches from the ground and center of pedal cranks was 14 inches. if I kept that dimension I should be fine. I still might try it. whats interesting is the rear pivot point is 4 3/8 inches wide. I might chop a hard tail and mount the rear triangle by the tapered bottom bracket and use the pedal bolts as the mounting point.
I bought a marin wildcat trail but cant make it work, an older rocky mountain rm7 looks like it might work but haven't found one for sale. there is another rat bagged ebike for cheap I might buy tonight, it has the 20x4.0 tires on it and I wouldn't feel bad chopping it up just to see.

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Re: scorpion fx

Post by SlowCo » Nov 19 2019 9:06am

What has the tire diameter to do with being slow when pedaling? That is just the gearing I presume? I suspect you're trying to solve a non existing problem with a wrong solution... :?:

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Re: scorpion fx

Post by goatman » Nov 19 2019 9:28am

it is a gearing problem but I don't want a huge crank wheel. I want to go faster uphill with pedal assist than the current setup will do going full out downhill. and a bigger tire solves the gearing issue

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Re: scorpion fx

Post by SlowCo » Nov 19 2019 9:41am

Then lace a DD 1500W (or 3kW...) motor in your 20" rim and get a bigger/stronger battery and controller. Sell the low power motor and controller you have to recuperate a little of the investment and off you go swiftly uphill 8)

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Re: scorpion fx

Post by goatman » Nov 19 2019 9:53am

mxus 3005 is 1200watts im lacing it 20inch wheel and the phaserunner is 96 phase amps, my battery is only 14s but it will be 16s soon. add statorade and I should be able to do 2000 watts but if you hit a hill with low battery you need to pedal. the phaserunner has field weaking so that motor might get upto 45mph but who knows til you try it. Doc Bass puts skis on his and hits the snowmobile trails. I cant fit a fat tire in the current swing arm which is another reason I want a bigger swing arm.

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Re: scorpion fx

Post by amberwolf » Nov 19 2019 9:59pm

goatman wrote:
Nov 19 2019 9:28am
it is a gearing problem but I don't want a huge crank wheel.
Is it a single chainline, or does it use a jackshaft?

If it uses a jackshaft, you can increase the gearing ratio at that point.

If it's a single chainline, you could add a jackshaft, but it does complicate the chainline to do this. One relatively easy option is to flip the cranks so the chainring is on the left, so it goes back to the left of the jackshaft, then the jackshaft passes it to the rightside to the rear wheel sprockets.

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Re: scorpion fx

Post by goatman » Nov 22 2019 12:29am

I hooked up my kit tonight, its a mxus xf40 DD in a 20 inch wheel, phaserunner set at max with a 52v/25r pack. had it in the kitchen to autotune the phase runner. I thought I would try it out and almost hit the tv. I wasn't expecting the torque off the line. I run a phaserunner on my other bike and its sluggish off the line with a 26inch OD tire on a 3540. its going to be a fun weekend

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Re: scorpion fx

Post by SlowCo » Nov 22 2019 2:30am

goatman wrote:
Nov 19 2019 9:28am
it is a gearing problem but I don't want a huge crank wheel. I want to go faster uphill with pedal assist than the current setup will do going full out downhill. and a bigger tire solves the gearing issue
http://www.efneo.com/gearbox/

http://www.schlumpfdrive.com/index.php/ ... drive.html

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Re: scorpion fx

Post by HK12K » Nov 22 2019 7:54pm

Please keep us posted on how this works out, preferably with lots of pictures! :bolt: :bigthumb:

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Re: scorpion fx

Post by goatman » Nov 22 2019 8:10pm

I took it for a 10km trip to get handle bar extensions for the ca and throttle(had the thumb throttle on my index finger kind of trip) its peppy. my phones crap for pictures, cracked lens so the pics are dark and if I use flash then all the reflectors go off. ill get a phone this weekend. im about to tear down and final build my stiletto that Ive been experiment/building so ill start posting in the build section

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