Crawler Canyon Tech Notes: Finding CGH (revisited and improved)

[@brianmassey7563]

That was awesome. I'm going to have to get all my rigs out and make sure my workbench is level. I'm really interested in the cross weight, and raised weight. I have too many rigs that unload on descent and I roll. I did notice your program was set to front wheels raised when you entered in all your numbers.

[@CrawlerCanyon]

Of course I would miss a critical point. Such is my way. I re-entered everything, and the CG moved up about 7mm-- which I'm fine with, as the number I got from doing it wrong seemed WAY too low. I can tell you that most CMS rigs seem to come out with their CGH somewhere near the top of the sidewall of the tire (portals generally making that higher still) so I'm -mostly- happy with how this guy is currently sitting.

[@brianmassey7563]

@@CrawlerCanyon I was hoping you'd re-calc and post. I'm really glad you did this vid...the all-out nerd in me is really excited to calc my rigs. I also just tore out a 12x16 concrete pad and I'm going to use it for my very own course! Repetitive lines will satisfy my nerd for testing.

[@machinedred]

Great video !!! Made me laugh when you said "this is where the metric system comes in handy" 😂 being an engineer I totally agree 👍

[@bouncingnoise]

Hey, thanks a lot for your content, you got me almost addicted to my daily dose of crawler canyon 😅 Today we bought 4 kitchen scales for 8€ each in a German discounter store, I really loved how the employee was looking at us while we were paying 😂😂😂 Have a good one, and please keep doing what you’re doing 😊

[@rcstories_ca]

Thanks for the updated video. Some time in the last year I tried using the Longacre calculator and, ya, it no longer worked. But the math explanation was still there (it’s just trigonometry), so I made my own spreadsheet to plug the numbers in and it’s been working great. The Longacre method actually has the front wheels raised which I like as for crawlers we are usually prioritizing improved climbing performance (it’s easier on my brain having the vehicle position analogous between the bench and the rock). Very handy to see the relative shift in CGH as changes are made and to compare that to real world performance.

[@soundmindtv2911]

Good info! You can adjust your cross-weight by adjusting your spring preloads, if you have adjustable springs. Cranking some preload into the corner you want more at, and/or out of the adjacent corner to balance it. For example, if your LR-RF is too high, you can take a turn out of the LR and RF springs, and put a turn in to the RR and LF springs, then settle it and weigh it again. Repeat until you have the balance of corner weight and ride height that you want. This can mildly compensate for small imbalances in physical weight placement. ☺️ (Edit: or achieve the same by adding and/or removing spring spacers, or even playing with spring rates, such as a slightly stiffer spring in the right rear than in the left rear)

[@soundmindtv2911]

@@BoomslangSuss no

[@soundmindtv2911]

@@BoomslangSuss because we aren't talking about raising or lowering just one corner. We're talking about "cross-weight" or aka "wedge." If you add preload to the left rear and right front together, it will raise the whole chassis. Then removing preload from the right rear and left front together lowers the whole chassis. The result in this example is more of the car's weight is distributed to the left rear - right front and less is distributed from right rear - left front. Test it on corner scales and you'll see what I'm talking about. It will change the car's handling and response to forces as the chassis sets and unloads through corners. This is one quick adjustment for getting a car to hook up better or loosen it up going into and out of corners, for instance. But it won't lean the car unless you put too much adjustment into one corner alone.

[@soundmindtv2911]

@@BoomslangSuss would you like to learn something new that could be useful? Or just be contentious? Because I don't think you're reading what I typed since your response is referencing several scenarios that I never suggested. Some background: I was a chassis tech on a Nascar team from 1990 to 1995. Full scale race cars. I can help people with chassis tuning if they don't let their pride prevent them from learning new things 😉

[@dkmgm2011]

Thank you sir! Would love to see this as a series. Or at least on the invitational finalist.

[@maritimezombie7684]

Great explanation on finding the center of gravity height. This method can also be used for any RC racers out there as well.

[@auggysimcity]

jazz is on point.. nice final cut intro!

[@DreamBigBuildSmall]

I recently found your channel and really appreciate these videos. I plan on trying to build a purpose built crawler for next years scale comp season and these are informative and easy to understand.

[@jimbocreationsbu8203]

nice jazz intro - ohh i will definitely do this mathkrobatics - i like mathematics - this is great - thanks for the meticulous down to the point simple explanation -

[@Andy_Yates]

This is great, and I'll have to try this out to see how it compares to my excel file from Rob Robinette. I use the CGH calculations to measure directional improvement. I bought my Amazon scales for about 10 bucks each and I use 1-2-3 blocks from my machine shop days for the raised height. You might want to pin Brian's comment so you don't get a 100 more comments about the 'front wheels raised' setting

[@alxe24]

Thank you for pointing me to this fantastic video and calculator. There are 2 things that I seem to be confused by and I can't pinpoint why. I highly doubt any of my rigs can have an H value 3 times as yours, even an RTR so I might be doing something wrong. I am using corner scales and yes, they are level and calibrated. and one of the rigs I'm using is an Enduro base axle on Gspeed V4 rails with 90MM schools leaning similar to yours on a power wagon Cab. 1) you made a pop-out note correcting yourself that H is measured from the axle and when I see the diagram on the calculator and read bullet point #6 quote "Read the resulting height h, which is the height of the center of mass above the ground" when I read that and see the diagram, I interpret it from the ground. Am I incorrect? 2) I went through the motions with 4 different rigs of mine, and the lowest I got is 7.43 CM "3 times yours" making me scratch my head as to how your rig is 2.381 CM which would likely be somewhere under the skid. Can you think of anything? In any case, I liked the video a lot, it is super useful to probably do it before and after making changes to a rig to see how those affected the ratios. FYI the numbers of the car I used were as follows. Car weight 2.924 KG Wheelbase 32 CM Front Axle Weight 1.649 KG Front wheels raised on (tamiya cans) 4.125 IN Wheel radius 5.7 CM Front axle raised weight 1.594 KG Car track 19 CM Left wheels weight1.468 Thank you for the great content you put up.

[@CrawlerCanyon]

I messed up-- it took me a few times putting the numbers back into the calculator right now to catch it-- I had the front axle weight for rear wheels raised but didn't click the mene to change it from front wheels raised, so it put the CGH as you said-- somewhere under the skid. The actual CGH was at the 80mm mark in the sheets, so I must have caught it then and then forgot. I have also gone to doing the calculations with both front and rear wheels raised, and taking the average. It's never going to be 100% accurate for us as we still have shocks and compressible tires, but it's good enough to tell when a change is working and when it isn't.

[@SlavaRC]

🥰🤩💥💯👍👏

[@user-6tfvk70k78]

Really good video 🤠

[@machinedred]

This is an awesome vid but you haven't really said why were doing this or it's real world example of what it's helping ,sorry to point that out ,it's still a great video and being more advanced in RC I can understand myself but for those new to this your not explaining to them why or what it's doing ,maybe over exaggeration with some weights on the car and drive it on your rocks in a controlled test ,to show what the changes are doing . Big thanks 🙏

[@machinedred]

Also compensation for torque twist in the props is another issue especially in cross weight on and off power IE the rigs always wanna be heavy in one corner on and then the opposite diagonal corner off power but mathematical I've no idea how to work that out 😂

[@meirdeaph]

The rusty green paint on that is awsome

[@CrawlerCanyon]

I you haven't tried a "patina" paintjob, I highly recommend it. I genuinely enjoy doing them, and that comes as a bit of a surprise, as I had come to loathe painting lexan bodies. That one started as the yellow shell from the Ecto RTR.

[@paulschryer9571]

- What is "CGH" !!??? Nowhere, can I find a definition, here !! 🤨

[@CrawlerCanyon]

Center of Gravity Height. CoG is a plane, CGH is a point.

[@machinedred]

As I said above ,people need a simpler explanation but this is an awesome vid for more advanced drivers

[@arifaminuddinaman2950]

What you oil shock ?

[@CrawlerCanyon]

If memory serves, Jake is running 80wt oil all the way around, because the shocks have the alternate red Traxxas pistons (higher flow.) I think with the normal black GTS pistons, he would likely be on 40 or 50wt.