View Full Version : ST3 Build 2021

03-16-2021, 12:43 PM
372203721837219I have started my ST3 build. I am trying to keep it strictly to the plans, want to reduce unintended consequences as much as possible. Built a 4’x8’ work table with leveling legs to start. I have the rogue fab m600 bender and their notcher. If anyone has any suggestions or knows where the plans need revisions please feel free to help out. I am 6’1” is there enough room in cockpit? Bought a set of mule takeoff wheels and tires 4x156 bolt spacing on wheels. If anyone has idea for front hub assembly without drilling and welding to existing hub assembly please let me know.

03-16-2021, 01:36 PM
looks great, that table will really help, I used saw horses and I wish I had that table.
Why not use Polaris hubs for the front, this will solve your issue with the wheels fitting the front. I'm not familiar with the plans but you'd have to modify and adjust to fit the polaris hubs.
Some Yamaha's used 4x156 on the front also, banshee's etc..

03-16-2021, 01:52 PM
For the front hubs, buggy will be 2 wheel drive, so do i just buy the entire assembly and pull the drive shaft. rzr hubs are internally splined, so would need threaded splined shaft to keep assembly together? any of the 2wd drive versions seems like they have drum brakes and i want disc up front. I am having trouble visualizing how it would work.

03-16-2021, 02:03 PM
You could use front hubs from a 2wd Polaris ATV with disc brakes. I used front hubs and a-arms from a Yamaha YFZ450, it has disc brakes, 4x156 hub, and the arms worked great, I just had to make mounting "ears" for the arms to my frame.

03-16-2021, 04:38 PM
I wouldn't worry about the parts being internally splined. A LOT of cars, trucks, and SUVs that are 2wd with a 4wd/AWD counterpart will share the front hubs, minus the cv axles, front differential, but will still use the same spindles and hubs.

Quick question for you though, does the ST3 plans call for 1" axle with u-joints? I know my ST2-NG plans call for those.

03-16-2021, 05:14 PM
Yes it uses 1" axles with j joints. i was thinking about using rzr axles with cv or something similar. no idea on engine yet, so will figure all that out later. we want to have fun and not die, so probably wont go for crazy horsepower. The only difference between ST3 and ST2 plans is the chassis.

03-16-2021, 10:45 PM
Where are you located? Most easily found engines are going to be motorcycle. If your north, and you don't want to shift, snowmobile engine. Since yours is the two seater, you may want to look for engines around 700cc and up, and gear it deep if you don't get any higher than 750cc.

03-17-2021, 12:39 PM
I am in west texas, Midland. I want to shift, so probably will find a motorcycle engine. I made my first tube with multiple bends, i was very concerned about messing this up. I drew out full size template on 5mm plywood, bent some sample tubes, 45, 30, and 60 degree bends marked start and stop of bends and measured 6" bend offset and everything went great. I need to work on keeping tube aligned in bender, i do have a couple angle cubes but need to get better at putting them on where they can stay on during the whole process. 37221

03-17-2021, 12:58 PM
I used to have a plywood sheet marked out like a compass so I could measure tubing angles, cuts, etc. Very handy at the time.

If this is your first build, then you will discover the 80/20 rule at some point. You'll get 80 percent of the buggy built, then things will sl-o-o-w down trying to get that last 20 percent done (ask K-fab about wiring). Just be patient and keep at it. ;)

03-17-2021, 05:35 PM
i agree on the 80/20 rule, we recently built a grandaddy go kart and solving all the "quirks" probably took as long as building it. just getting it to stop safely was a huge learning experience. 3722237223

03-18-2021, 01:40 AM
Per the plans seat to pedal is 36-42 inches. I am 6’1”. Thinking of stretching the frame 6” to make it comfortable to drive. Let me know if anyone has experience or comments. Doesn’t seem like it will be too hard as long as I draw everything out and bend cage per drawing.

03-19-2021, 04:32 PM
Overall height doesn't matter much as your leg length does. I'm 5'9", but I have a 34" in seam, similar to my brother whose 5'11. What may work for you is, setting up a seat you'll use in the buggy at the height itll be mounted at, with the seat leaned back or not. Then get yourself in what position would be the most comfortable, then have someone mark where your feet will be at with tape. Then measure it out. Then you can see if you need to modify the plans for that or not.

03-21-2021, 11:41 PM
Thanks for the info. Does anyone have a recommendation for a pair of seats that will fit a five point harness. Looking for value. Willing to spend $300 or so. Trying not to break the bank on this build. There are rzr seats with harness cutouts on eBay for around $300 with shipping. Let me know if you have suggestions

03-22-2021, 03:52 PM
I'm looking at 3 of these. One for my ST2-NG and 2 for my VW buggy I'm building. Seats should be more comfortable with the padded seat covers. If you have like a Speedway motors in town, I'd go there and try out seats they have. https://www.jegs.com/i/JEGS/555/70250/10002/-1?gclid=CjwKCAjwgOGCBhAlEiwA7FUXkigXMuLDOg-G5qFAdpyK40uNm2v0dCO0ym_C4M98j9lP_4yxmGYxWRoCWBEQA vD_BwE

03-22-2021, 05:14 PM
I have two of those in my go kart. they are pretty cheap. the nuts are just molded into seat and if you overtighten bolt they will come loose, this happened and jegs replaced at no cost. after you buy the seat pad and the vinyl cover they are about $100 each. the sliders are terrible. just make sure you have the seats and sliders before you drill, the holes are not as described and slightly at an angle. I think it would be worth the extra $50 and get some rzr seats with harness passthrough. my$.02. once you get them installed they are fine, just not great quality.

04-05-2021, 07:58 PM
Got some more progress on tube bending and tacked together base frame. Need to order some 1.5" tube for the butt joints on mid frame. Also built a weld/fab table and got parts from water jet. 37231372323723337234

04-06-2021, 02:48 AM
Were you able to get the cad files or did you just take the plans over to a water jet to have them cut out? Did you get them to put in the assembly tabs to make it easier?

04-06-2021, 12:39 PM
Cad files came with plans, i just emailed them to shop and they cut them. They did have assembly tabs from the the plans, and everything joins together pretty good. Material thickness was also included in the cad files. I am going to try and strictly build to the plans with exception of rear end. Will try and use CV instead of u joints. if you are using car/utv axle spindles you might not need many of the pieces cut. I did email badland and they sent the front a-arm jig for free, as this cad file was not included with the plans.

04-06-2021, 08:07 PM
Sounds like quality progress.
Laser parts - done correctly they fit like LEGOs which is really nice.
Probably doesn’t need to be said, but tack, tack, tack then weld fully once you have the stuff assembled.
Keep up the great work.
If you can ditch the U-joints and adapt 930 CVs (especially if you can run the non-plunging if there’s no axle plunge) and you’ll have a more bulletproof drive train.

04-07-2021, 01:23 PM
It does need to be said, i think i need to get a sign printed for the shop with that on it. TACK, TACK, TACK, then wait, then wait some more, then wait some more and then Weld. Thanks for the info and comments.

04-07-2021, 02:50 PM
My very first set of upper arms for my first ground up build we’re great. All three sets of them (was used to wadding Pilot arms whilst racing) so I was making spares to have in stock.
Looked good, fully welded, ready to bolt on. Yeah!

Then I tried fitting a pair and they hit the shocks. Was a very minor fix and if I had tacked, it would have been an easy correction. Lesson learned. Tack, tack, tack.

04-08-2021, 01:53 PM
I got some 1.5” tube to fit inside the 1.75” tube so I can butt join and plug weld the mid frame together. Is there any rule of thumb for how long the 1.5” tube should go onto the 1.75” tube. 3” on each side?

04-08-2021, 02:22 PM
My stub tooobing joints (too many in the Mini...) are only 3” long overall. Once welded fully it thinks it’s one piece of tubing again anyhow.

04-19-2021, 02:40 PM
Got mid frame tacked together and driver hoop tacked in. this took a lot of "adjusting" notches with grinder to get bar level and a good fit still needs more, but have to be careful as i cant shorten the bar anymore or it will be narrow. If anyone has suggestions on joining a tube on a bend let me know. 37247

04-19-2021, 03:33 PM
get a paper towel roll or toilet paper roll and slip it over the tube if possible, then push against it and get the desired indentation/fit and then trace where it goes. Be sure to mark an indicator line on the tubing as well as the towel roll or assistant marking to make sure you align your marks properly afterwards. If you aren't on as much of a budget, there are some nice handy magnetic ones that the welding supply stores typically have in stock or amazon....https://www.amazon.com/PipeMaster-P-T1625-1-5-8-Tube/dp/B01AYJOHQE/ref=asc_df_B01AYJOHQE/?tag=hyprod-20&linkCode=df0&hvadid=312128028232&hvpos=&hvnetw=g&hvrand=7288006238474071897&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9019054&hvtargid=pla-597718550364&psc=1

04-19-2021, 06:25 PM
thanks for the link. just bought it. got rear brace tube fit. the driver hoop tack welds look bad, may have to cut it off grind and start fresh. got pretty rough after being tacked 4 times. 37248

04-20-2021, 12:28 PM
I just sent the link to the first one I found... hopefully you got the one that matches your tube diameter :-) LOL.

04-20-2021, 01:33 PM
I bought 4 fresh takeoff mule pro wheels and tires. They are 4x156 bolt spacing. For the front I planned to use the Polaris trail boss idler hubs. They will need to be trimmed to fit inside the 4” wheel opening and they use a 25/32 spindle. They do have brake rotors as I want to have front brakes. Will this be strong enough. Should I start over or maybe get different bearings that will accommodate a larger spindle?

And kustomfab yes I ordered the right tube diam.

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04-21-2021, 01:48 AM
They should be fine for an ST3.

06-01-2021, 12:57 PM
Got frame tacked. Still have support/cross braces to put in. For the a arms seems like using Heins would be better (except for cost) to attach a arm to the frame. Plans call for sold round bar and clips.

Any suggestions? https://uploads.tapatalk-cdn.com/20210601/f795e31f98afaae6ba564a116e31b016.jpg

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06-01-2021, 06:02 PM
Lower arms can be done with just bolts and pivots running on plastic bushings. Up on top, I'd do heims - gives you adjustment ability.

06-01-2021, 08:53 PM
Thanks, that makes sense, is the adjustment on the top to ensure that the pivot points are coplanar? both a arms will have a adjustable heim at the end that connects to spindle, what would the adjustment at a arm/body connection be for?

If you are aware of a build thread on this that still has pictures let me know. i have a hard time searching and dont really know what i am doing wrong.

Thanks for your help!

06-01-2021, 09:45 PM
Start here: https://www.minibuggy.net/forum/projects-progress/19848-mini-raptor-k-fab-style-117.html#post324038

Solidly mounted lowers, adjustable uppers. With the two heims I can make all the adjustments needed.
Lowers are Delrin inserts with a steel sleeve and a 1/2” bolt thru each pivot.

Actually you don’t want them to be coplanar, at least looking from the side of the car in, point of view. The front pivots need to be farther apart than the rear so you induce caster changes (2ish degrees) during cycling. Keeps things more stable.

Don’t know if I sent you here yet but read the whole thread: https://www.minibuggy.net/forum/suspension-wheels-tires/19394-how-design-build-arm-suspension.html

06-05-2021, 12:47 AM
Couple questions for the group. 1) front suspension block, the plans called for the pivot points on the upper a arms to be wider than the lower, based on the suspension post i assume this is to help with scrub angle, i made the pivot points for upper and lower indentical and made upper and lower a arms identical (by accident) is this a problem? i could make upper a arm pivot brackets longer to correct for this but seems like they would be weaker.

I purchased 4 fresh takeoff mule pro fxt wheels and tires (4x156 bolt spacing) and atv free wheeling hubs, i purchased a trailer stub axle that will need to be turned down to fit inside hub bearings. this seems fine, but i think i have a few options 1) buy trailer hub 4 on 4, and buy new wheels 2) replace bearings on hub that will accept 1" stub axle/spindle 3) have trailer axle turned down to fit with hub.

Seems like using the mule wheels and tires will be easiest especially for rear, as i can buy rxr/mule internally splined hubs and use rzr/mule axles.

Let me know your thoughts, really appreciate all the comments. 3729137292

06-05-2021, 12:49 PM
Finding bearings to fit might be tricky, but it's probably the easiest option. I suspect that you'll need to have the axle turned down to make it fit.

06-05-2021, 02:51 PM
Nice work on the chassis so far!

The reason they have the upper, inner mounts spaced out farther than the lower mounts is to allow your front tires to travel proper suspension geometry. The proper geometry is when the tire comes up to full bump (bottom out suspension) the bottom of the tire will push out and the tire will gain negative camber. Same thing happens as the tire drops to full droop as a result of the different a arm pivot point locations. But, to make this work properly, the top a arm must be shorter than the upper a arm (shorter upper a arm creates a smaller radius when it cycles and thus pulls the top of the tire in when it goes up and down).

Having your suspension all parallel (same top and bottom mounts and same a arm length) will result in larger amounts of scrub like you mention. It could make the front end feel ‘washy’ since the tire needs to push sideways as the suspension compresses so the tire is no longer rolling only, but also sliding sideways. Also, when you turn a corner, since the chassis will “roll”, called body roll, the tire will angle outward into positive camber (not desireable) and cause the tire to ride on the outside edge of the tire only and not on the flat contact patch of the tire. If you have negative camber gain like mentioned in the above paragraph, the tire angles the opposite way and helps maintain a flat contact patch with the ground (tire tries to stay perpendicular to the ground).

All of this being said, the buggy will still work good and you shouldn’t have major issues driving it, but a proper suspension geometry will make it more enjoyable and a smoother ride.

As for your hubs, I would keep the RZR/Mule hub you have in the photo and turn down the axle to fit the existing bearings. I think that sounds like the easiest solution. That way you can run your original tires and just weld the stub shaft into your spindle to accommodate the rzr hub.

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06-23-2021, 07:57 PM
Front A-arms tacked and installed. still might move pivot point out on top a-arm3730537306 and shorten top a arm to go back to plans cant decide. Working on a jig to make rear a-arms.

07-26-2021, 06:50 PM
All, i have made a lot of progress on the buggy front suspension and steering is all sorted out. I changed the tabs on top front a-arms per the plans and also relocated the steering rack/tie rods behind the a-arms to allow for ackerman angle.

I found a machine shop to turn down the trailer stub axles, but have a question on rear a arms. I need 40mm ID Bearing to hold the hub, if i order the correct bearings for a mule they have too large O.D. to fit inside the bearing carrier (turned 2.5" Sch 80 pipe) i made from the plans. Is there any rule of thumb on what size/type wheel bearings i can use, i dont want to go with too small of a ball bearing and have an issue. Any thoughts are welcome. I should have ordered the entire MULE/RZR bearing carrier/hub assembly but the rear a-arms will not a37329ccomodate this.

08-19-2021, 02:27 PM
Got front end figured out. Used Trailer stub axle and 5x4.5 trailer idler hub. Put 11 1/4' rotor on them fits great. Is this too big? does it matter? Bought inside splined wheel hub and bearing assembly from a non ABS 2000 ford ranger and ranger axles for rear end will have to convert a flange for center spool. Trying to do all of this with minimal machining. 3734237343

08-19-2021, 02:51 PM
[QUOTE=buggy;336074]Got front end figured out. Used Trailer stub axle and 5x4.5 trailer idler hub. Put 11 1/4' rotor on them fits great. Is this too big? does it matter? Bought inside splined wheel hub and bearing assembly from a non ABS 2000 ford ranger and ranger axles for rear end will have to convert a flange for center spool. Trying to do all of this with minimal machining.

Also had a question on front shocks. Plans call for FOX 2.0 Air shocks with 4" travel up front and 14" travel in the rear. Seems like most people are using longer travel shocks up front. Are there unintended consequences to going longer travel? also i am assuming that longer travel up front is better but dont really know for sure? Any thoughts are helpful.

08-19-2021, 03:35 PM
The 4" is the max shock travel or total travel?

To much travel can bottom the frame out on the ground. This can hurt your spin. It can also max out suspension joints and bend parts. Other than that it's a good thing in most situations.