Building Knowledge

[Jonny Eff]

Hi guys.

I'm a Lockdown newbie. No hating please!

I've built up a Racing Fighter, which I absolutely love, but figured it's too quick for The Boy so I've ordered a Mad Bull for him to bash about. I can see this never ending 🤣

Anyway, I'm keen to learn more about all the technical stuff, building fettling etc, why different suspension affects handling and also techniques.

Is there a Holy Bible I should read, or a particular website or two? Help much appreciated.

[Badcrumble]

Welcome!

You're right, it is never-ending....

If you are going to keep building Tamiya  and don't have them already, a Tamiya screwdriver set would be a good investment

https://www.makeitbuildit.co.uk/tamiya-rc-tool-set-8-pcs-60383?gclid=CjwKCAiA6aSABhApEiwA6Cbm_2z6Og4b5bIlD2pyGLFWAPejjDfHRiW_dNjTYNTb9GAagAhc1IcZvhoCHbcQAvD_BwE

or

https://www.modelsport.co.uk/index.php?product_id=388188&gclid=CjwKCAiA6aSABhApEiwA6Cbm_8x0bCvm_3kpRRQwsMl8Lf6xhQmvWyprsBQGP6uWix5uqo18UYvy8xoCjRwQAvD_BwE

A lot of guides are aimed at racing on-road touring cars, off-road buggies or short course trucks. There are some basics here

https://site.petitrc.com/reglages/BasicSuspensionTuning/

http://www.thercnetwork.com/rc-cars/category/beginner-series/

The Mad Bull is a good starter basher, known as very hard wearing. Have a look out for the steering mod in this build thread

Have fun!

[Jonny Eff]

That's perfect. Thanks dude.

[Wooders28]

Welcome!

2 cars already! You sound like you're settling into the a̶d̶d̶i̶c̶t̶i̶o̶n̶ hobby quite well....🙄

As for technical stuff, I've found you never stop learning, (I'm over 35yrs so far....)  so it depends how deep into it you want to go! 

For building , I've found the better the dedicated tool selection, the easier /better the building experience (and sometimes better end result). Things like ,Shock pliers, make building shocks a doddle, no marking the shaft (causing leaks and notchy shock action) etc, and also a ,Shock stand (my pit stand has holes for holding shocks) ,makes filling them a doddle ,and then a ,Shock vac pump, makes getting all the air out of CVA shocks a doddle etc etc, but it all depends on ,how many times are you going to use the tools? 

 

Touching on shocks, you've friction shocks and oil filled.

In the friction category there's 2 (i think...) just springs ,like the front of the grasshopper /hornet / lunchbox etc, essentially just like a pogo stick ,push it down, it springs back up. So like a pogo stick, they bounce ,rather than ,Shock absorb = rubbish imo...

Then there's friction shocks, which are the same as the ,pogo stick, but housed in a shock body, so offer a bit of resistance/friction where the shaft goes through into the shock body, but still fairly useless imo.

There's 2 types of oil shocks (again, I think...), 

CVA (Constant Volume Adjustable) and Aeration. As you can't compress a fluid, you need to have a way of adjusting /compensating the volume in a shock chamber, to make room for the shock shaft volume when the shock is at the top of its stroke vs fully extended. 

The CVA use a rubber bladder, which deforms,  so you fill the shock with the shaft extended, wait for all the air to escape (quicker with a vac pump), fit the rubber bladder, and screw on the cap.

With Aeration, theres no bladder, so you fill the shock, fit the cap, undo the bleed screw, push the shaft up, tighten the bleed screw. The chamber then has just enough air gap ,to allow for the shaft volume.

Oil shocks (well, dampers), are so much better for buggy handling, as they follow the bumps,  rather than just bouncing. This means you can go quicker ,and with better steering, as the tyres are in contact with the ground more of the time. Then you're into oil thickness ,and piston hole number / hole diameters, which depends on the terrain and buggy weight (heavier buggy needs thicker oil etc) 

[Jonny Eff]

Thanks Wooders.

I've got a long history in mountain biking, building and servicing my own bikes Inc hydraulic brakes and suspension so I know all about getting addicted to expensive hobbies🤣

The wife seems less keen🤣

My racing fighter's rear shocks weren't rebounding to start position when I push down on the back of the car. I've got cva shocks with oil dampers using the stock oil. I've added in all the spacers to shorten the spring length, which has helped, may invest in a firmer spring.

[Mad Ax]

1 hour ago, Jonny Eff said:

My racing fighter's rear shocks weren't rebounding to start position when I push down on the back of the car. I've got cva shocks with oil dampers using the stock oil. I've added in all the spacers to shorten the spring length, which has helped, may invest in a firmer spring.

Do you mean rebounding to the static sag position, or to fully-extended?  Some static sag is desired, otherwise the rear wheels will come off the ground whenever the back is rising.

Also note that if you're testing the rebound on a grippy surface, the tyres will grip onto the surface and resist the lateral movement as the suspension arms move through their arc.  When racers set their suspension they usually use a setup deck, which basically consists of a smooth flat surface and some bits of perspex that bolt on in place of the wheels (this also lets them set up toe and camber angles by measuring the angle of the perspex relative to the centrelines of the car).

On these lightweight cars it's normal for compression sag and rebound sag to be slightly different due to friction in the suspension movement, which isn't so obvious on much heavier full-size vehicles, but if it's a long way out you could investigate for excess friction anywhere in the suspension components and also look at a product called Green Slime made by Team Associated, this is a lubricant that you put on your shock shafts and stops them binding up on the rubber O-rings.

[Problemchild]

Tip 1. Always remove the plastic burrs with a knife  

JJ

[Badcrumble]

1 hour ago, Mad Ax said:

 you could investigate for excess friction anywhere in the suspension components and also look at a product called Green Slime made by Team Associated, this is a lubricant that you put on your shock shafts and stops them binding up on the rubber O-rings.

Or if you are in to MTBs, you may already have o ring lubricants for forks, etc.

[Baddon]

Welcome, no hating on this site, we all started at our start point and happy to help others where we were not so long ago.

The Madbull is a great started buggy for kids, just steering linkage lets it down after some impacts. It has friction shocks (pogo's) certainly worth if you can pick up 2nd hand changing to oil esp on the rear. 

If it has a trigger controller then a little peice of rubber behind he trigger will limit top end for a bit if needed. I use this on my little ladies Madbull.

[Jonny Eff]

2 hours ago, Mad Ax said:

Do you mean rebounding to the static sag position, or to fully-extended?  Some static sag is desired, otherwise the rear wheels will come off the ground whenever the back is rising.

Also note that if you're testing the rebound on a grippy surface, the tyres will grip onto the surface and resist the lateral movement as the suspension arms move through their arc.  When racers set their suspension they usually use a setup deck, which basically consists of a smooth flat surface and some bits of perspex that bolt on in place of the wheels (this also lets them set up toe and camber angles by measuring the angle of the perspex relative to the centrelines of the car).

On these lightweight cars it's normal for compression sag and rebound sag to be slightly different due to friction in the suspension movement, which isn't so obvious on much heavier full-size vehicles, but if it's a long way out you could investigate for excess friction anywhere in the suspension components and also look at a product called Green Slime made by Team Associated, this is a lubricant that you put on your shock shafts and stops them binding up on the rubber O-rings.

Thanks Mad.

Originally, when I first built the car I had it stationary on a table and pressed on the rear. The shocks compressed fully, but didn't rebound at all. Just stayed there. Adding in the spacers reduced the spring length, thereby increasing spring strength, has helped. It'll be a bit of trial and error I guess to reach a happy medium of bounce vs wheels sticking to the ground. 

I ride downhill and bike park mountain bikes with big suspension, so I'm pretty used to setting sags on them to ensure the wheels stay on the ground over rough stuff.

Cars are different, because I'm only just learning to feel how they drive.

I like the idea of some stiction in there. I've got some mtb suspension oils and lube which could well help the situation.

[Wooders28]

22 hours ago, Jonny Eff said:

I've added in all the spacers to shorten the spring length, which has helped, may invest in a firmer spring

It's a balancing act, if you go too stiff with the springs with thin oil weight,  you just end up with the pogo stick effect. 

As above, you defo want it to sag under its own weight, otherwise the car lifts, instead of the shock taking the hit.

I a race car, I run around 20-25mm ride height when off road, and 15-20mm when on flat carpet. Check with full weight (battery, body etc), then put the car on a flat, solid surface (worktop etc), push the car down, bottoming the chassis and let rise itself, then measure the height front and rear. Much easier to adjust when you've the ,screw threaded shock body, but you should be able to get close with the spacer clips.

You tend to want the rear softer than the front, otherwise you'll find the rear kick up more over jumps, and unless you've a bucket of power, you won't be able to pull the nose up punching the throttle.

I'd run it, and see how it handles, ideally you want it soft enough that it doesn't bottom out over bumps and small jumps, but like MTB's, it'll depend on the height of the jumps and car weight etc, if you've big jumps, you'll need to find a happy medium between, the car bottoming out over the big jumps, and the handling the rest of the time.