InspGadgt

Interesting project you have going there John. Not sure how long you've been around in pan cars but you might want to look up the PB Sizzler and the TRC Lynx. The PB Sizzler used a 4 link with a pan hard rod for rear suspension and the TRC used something more similar to a triangulated 4 link by using 2 upper links and a center lower pivot on belcrank to actuate the shock. They were very interesting cars in their time but lost popularity due to the complexity of constantly adjusting 4 turnbuckles to keep the rear end square. I was working on a similar 4 link at on point but gave up when the EV10 came out and started running that. The only thing I couldn't get over with the pan hard rod suspension is the lateral movement of the rear axle due to the arc of the pan hard rod. It didn't seem to effect the car's handling but just nagged at the back of my mind. Recently though I've gotten back into pan cars in 1/12th and the inventor in me is working again on an idea of my own that will work like a 4 link but only have the upper 2 links adjustable to keep things simple. I just can't decide to use 2 shocks like a normal car or 3, 1 for bump and 2 for roll like current pan cars use. I rather like having the bump isolated seperate from the roll because you never have a problem with too stiff a bump just to get the right roll.

John Stranahan

iTrader: (27)

Marty-I notice that the long radius rods are an important part of that rear suspension. It also looks like to me that the car cannot roll on the suspesion at all (unless two of those links telescope like a side dampener). It is fixed in rotation by the four links attached to the solid plate. I don't think that would be good for a pan car as we usually set the rear roll stiffness quite loose to retain rear grip. Now if you reduce the number of links at the rear to two you could get some roll and if you fix the plate to the axle and the side links one high and one low to the frame you would have a Watts link.


Inspgadgt-I see what you are talking about adjusting the links. Having these huge links will helps some in that respect. A production version of this suspension could also use constant length lower links like on the stock Pantoura.

I note your problem of being able to set roll stiffness and ride stiffness separately at the rear. I'll have to test this to see if this is a problem. I was looking for better return of the tire to ground after a bump by having the spring and shock act more directly on the wheel. Thanks for the report. I'll see if I can locate pictures of those other two cars. Maybe I was fortunate not to be influenced by their design and maybe not.

I found pics of the Lynx- Some good things are that you free up a lot of space making custom side plates and axles. The motor may not have a lot of adjustment fore and aft, though. The Panhard bar is very short which makes the problem of the arc of movement more severe. Here is a link.

http://www.rccars.stuandcathy.com/html/sizzler_4.html

InspGadgt

Yeah the longer the pan hard bar the less sever the pod movement will be. The Sizzler pictured there is built a little differently then the ones my friends ran. Theirs had a verticle shock mounted to the front of the rear pod.

John Stranahan

iTrader: (27)

Here is another sizzler shot. The links are also very short on this car and attach to the front of the pod. They probably need constant adjustment because they are small for the job they are trying to do. The motor is heavy. I appreciate all this info you guys give me. That's why I do these things in public. We both can learn things.

My design criteria was long links, long low Panhard bar, shocks right on the wheels. This was gleaned from the books I have on hand as well as the hypothesis that the shocks and springs would work better for bump control at the wheel.

Note that there are several pics and discussion of my new four link rear suspension with Panhard bar on the previous page, If you have not seen them already. Look for red suspension links.

InspGadgt

well the main reason they need constant adjustment is from getting knocked out of whack anytime the car hits something...longer rods really are not going change that so long as the rods are adjustable. That and anytime you clean and rebuild the car all those links have to be re-checked. Also the twisting motion of the pod will work with the tie rods to change the length if it twists enough to turn a rod end. That's why I'm looking to use non-adjustable links like CRC does on the Carpet Knife cars. The adjustability would be nice for those who know how to use it to fine tune their cars...but for the vast majority of racers I think they'd rather have it non-adjustable to simplify things.

I've seen the pics with the red links...nice looking car...but my observations of the past still hold I think.

John Stranahan

iTrader: (27)

I have noticed on my touring cars that camber and steering links that change length in a crash are often caused by the metal threads actualy skipping from one plastic thread to the next. Telescoping rather than turning. These large red T-max aluminum rods have huge threads compared to the #4 threads. It is very hard to turn an end by hand. The pod will only turn a thread if the pivots bind. These seem to be reasonably loose. Time will tell. I agree that if you plan to manufacture links the lower links should be fixed. The uppers need adjustment to level the pod as you adjust antisquat. (Upper link angle)

Four Link Suspension, Left Side Frame Rail
Here is a pic of the left side frame rail. It will have three duties. At the front it supports the side of the battery and strengthens the frame edge. In the middle it will be the base to hold the small shock towers. At the rear it will support the Panhard Bar. There will be a similar rail on the right side but it will not extend back past the main frame plate.

The car looks like its going to weigh about 46 ounces with the twin batteries on board.

I have a pinion meshed now and the batteries in their running position about 1/8 inch in front of the motor.

The second pic is from the rear. These may not be the final parts here but they will allow me to test the car. Clearances are tight but the bar is pretty rigid. I may have to sand some more clearance in.

InspGadgt

cool...do you anticipate any issue with flex in the frame rail? What about rear end collisions bending the pan hard rod?

John Stranahan

iTrader: (27)

InspGadgt- Thanks.
I have put the car on the side with the tubular frame rail (1 G) load. The flex was only about .010 inch. This frame rail is of a larger dimension and solid instead of tubular. The flex should be less. It feels good and tight on the bench. At 3.5 g's it may flex only a tolerable amount. I will have to look for wear marks on the pod and tire. I can increase clearance or add a graphite top to increase the height of the rail at a later date. The T-max pushrod that I have used for the Panhard bar is hell for stout. You may bend it in a severe crash from the rear, but not from the side. ($5 bucks each) Those two servo mounts that the Panhad bar is attached to have some flex in a crash and will probably save the other parts from damage. If I break the frame rail I will make a taller piece.

A collision from the rear sometimes takes out the spur. It has some protection now.

John

John Stranahan

iTrader: (27)

Angled upper Links Did not work with Panhard Bar

Just a note that the car which is almost finished would not roll on the bench with angled upper links. I moved them a little, rear out, front in, so that they are parallel to the bottom links. Problem solved. What I had was a high and low roll center at the same time which prevented roll. I finished the right side frame rail. Just need to get my shocks. They were shipped yesterday.

John

AdrianM

iTrader: (4)

When you are done put all your electronics in an RC10L2 and let me know which is faster

slicvicpr87

WOW now that i see it all coming together i must say i am very impressed....that car looks like a monster!!!!!! Hey john where did u get your engineering degree!?

John Stranahan

iTrader: (27)

AdrianM- I have two almost identical Pantoura Based Cars. I will test them against each other. Both will be wide chassis. The more traditional car is like the Pantoura, a link car, but has home added front shocks which helped a lot. I have a suspicion that that L2 will have trouble at the end of our bumpy straight. It will probably fly as well as have traction problems over the bumps at the far end of the straight. I don't have one to test. I have not reported that my four link car is a superior car or design. I wanted to test it. It is quite interesting.

On the bench the four link car is very supple like I wanted. I have 3/4 inch of rear wheel travel available if I want that much. Plenty of droop. This may keep it hooked up over the bumps or maybe not. Testing will tell.

No engineering degree. Plenty of other degrees. I do some tinkering and read some books.

Pic is of the new upper link position. Parallel to the bottom links when viewed from above. There will be a new "knife" that is bigger, connects all four posts and has a pad to mount the speed control at the very back above the batteries.

AdrianM

iTrader: (4)

Some of the coolest stuff every made was designed on napkins over a few beers.

Pro ten Holland

iTrader: (1)

John, make sure you tune out most of that droop. Too much droop will make for too much weight transfer coming into a corner.
With too much weight suddenly shifting to the front your car will be very twitchy on corner entry, making it loose its momentum.

John Stranahan

iTrader: (27)

Mathijs- I will try short stroke shocks first, but will be able to put some long stroke shocks on if neccesary for a test of huge droop. Who knows exactly what this suspension is going to do on corner entry. The full size car guys like lots of droop with a solid rear axle.

Three Trailing Link Rear Suspension with Panhard Bar

I have come up on a problem of scaling which I will describe briefly. When you scale a car up 10 times (1/10 scale to full size) the dimensions and thickness of every part would increase by a factor of ten. The strength of each part increases as the square of a dimension so would go up 100 times for simple shapes. The weight however increases by a factor of 10 x 10 x 10 or 1000. So if you take an RC car and scale it up keeping every shape the same you would have a very wimpy car. The weight increases much more than the strength. The weight has increased by 1000 but the strength by only 100. Conversely if we scale a big car down to RC it becomes very stiff.

When I built a new top plate for my four link this made my four-link setup really stiff in roll. It would not roll at all. For a four link to work there has to be flex somewhere as one top link tries to lengthen and one tries to shorten. This is not a problem of angle as I have parallel links now. On a big car, parts flex to solve the problem. The rear axle tube acts as a big sway bar and probably twists some to compensate for the length change. On my car I have decided that I need a three link. Identical to the mustang suspension whose URL is above.

Man is the rear of the car supple in roll now. Almost done. We are machining lower shock mounts in Aluminum, but I need to locate a 2.5 mm tap.

The speed control and receiver may be mounted high and back now, the speed control close to center, and receiver close to the outboard edge now that I lost my center postion.