How Overdrive Defeats Anti-Squat on RC Crawlers

[@AnyAssumptionBanter]

i'd like to see no OD now vs this OD as well for comparison and a change in both height and amount of OD for further comparison.

[@alanworley1883]

Great video! Through trial and error I came to the conclusion that a link riser had little to no effect on the rear shocks staying extended but I never really made the connection between AS and OD. Thanks for simplifying an often misunderstood topic.

[@BoomslangSuss]

Happy to hear your test results match up with the physics. OD is one of several reasons AS doesn’t work in slow crawling situations that’s super easy to demonstrate. I’ve got other vid coming soon. Thanks for watching.

[@independentmind1977]

VERY informative, I've shared with one of my favorite RC groups on FB. I also have a background in cycling like you and find some of the Engineering knowledge to be transferable. Keep it up, I'd love to see more, especially on shock setup etc.

[@HolmesHobbies]

Great vids mate!

[@BoomslangSuss]

Thank you! That means a lot.

[@theoalbert897]

The biggest thing you are missing is the physics of when the rear end has grip regardless of what the front is doing the rear is still creating an anti squat reaction in the rear anytime there is load on it.. in a real world scenario sometimes it's a whole different ball game.. in a slow slow crawler with over drive its not overly noticeable but it does change alot when it comes to how the suspension actually moves around.. personally even my slowest crawler with over drive can still rip a wheelie so yeah that anti squat makes a big difference when the front wheels have no weight on them..

[@BoomslangSuss]

If you have over/under drive one set of wheels has to be slipping. If the rear has grip, you are right, AS will be actuated. However, most crawlers have a forward weight bias and the rear wheels are slipping. This is what is demonstrated in the video. As you start to go up hill, your weight bias naturally shifts to the rear and you start to get more traction in the rear as you point out. Also remember, AS is a dynamic response to a dynamic weight shift. If you are crawling at a slow speed AS doesn't do anything. I published a couple videos on that topic.

[@DurpVonFronz]

Personally I think overdrive is a bad idea for crawlers and much prefer underdrive. This way you still get that overdrive of the front but your not increasing wheel speed which to me is awesome for slow accurate controlled climbs. If your running brushless motor, it should be able to still give you that burst you may or may not need to get past some tricky areas of the climb. I run anywhere from 12% od all the way to 33% and recently moved to 33% ud on my micro crawlers. The overdrive is really only useful on high angle climbs where I notice it helps pull the front end over and keep it stuck to the hill. Without it the rear tires that have most of the traction just end up pushing the rig off balance really fast and make it fall backwards nearly 100% of the time. Good info and vid. Just took a quick glance at your channel and its the best stuff, mountain bikes and RCs. Still have my 2006 RockyMountain RMX 2.0 and that thing has some of the kewlest looking rear suspension of any mountain bike Ive ever seen :)

[@andretinker1109]

The AS is getting important when you're on a hill and the front has no traction. In that case you can bump without getting the rear shocks compressed that much.

[@BoomslangSuss]

Yes, you are exactly right. When you punch the throttle that’s exactly when AS deploys, and you want the correct AS setting. Acceleration bump from a throttle pop.

[@RCRoads]

Very informative video. Awesome job!

[@RCDR1000]

weight transfer due to acceleration, changing the height of the links will decrease or increase the squat but there will always be force on the rear when going forward

[@BoomslangSuss]

Force = Mass x Acceleration. If you are moving at a constant speed then there is no force except tire rolling resistance, aerodynamic drag, etc.

[@opivyx]

Always wondered how to calculate anti-squat with the ridiculous torque split that is over drive. Now I know it’s not really that important.

[@manta1121]

Nice video❗ good job my Friend 👍😉

[@texomarc]

This is cool but not real world. Overdrive isn’t for flat ground. Overdrive is literally for when the fronts are unweighting, so over 45°, especially as the rears are hitting the wall (bite) while weighted. This demonstrates the relationship but does not show what it’s actually for and why it’s important. We do tons of stuff that’s not done 1:1 but there’s not a 1:1 that’s going to be as capable as those crawlers. If you’re not pushing the limits vertically, overdrive should be minimal or not necessary. Also, overdrive is huge in high angle descent. Thanks for sharing.

[@texomarc]

Also, it’s not a bad thing for your hips to drop on a super performer. Having weight above the axle, like a heavy body, functional anti-squat becomes quite important. On a sporty with weight at or below the axle, the anti-squat still pushes the front of the rig into the hill, even when fully collapsed, if it’s setup properly.

[@BoomslangSuss]

I completely agree!

[@FPVDiverBomber]

So what do you think is best ? Not using overdrive? Now I want to see same test without over drive...

[@BoomslangSuss]

Overdrive is very beneficial to slow crawling. Anti-Squat does nothing at slow speeds. So depends on how you drive.

[@calinutz13]

Nice video, verry informativ both of them. Can you do one explaining torqutwist and how it can be eliminated or reduce ?

[@BoomslangSuss]

That's a great suggestion. Unfortunately, there is not a lot that can be done so long as you have a chassis mounted motor and drive shafts. You can't solve it with linkage. Great topic for a video.

[@Greg.Bosworth]

what are your thoughts on portals vs straights? portals pull on the upper link while straight axles push on the upper, which borderline gives the "opposite" squat effect than desired on portals vs straights. would love to see this test done again on a straight axle to see how the results compare. good stuff

[@BoomslangSuss]

I can see why someone might think this, but the reality is that the axle housing can only rotate opposite of the wheel rotation. Doesn’t matter portal or straight.

[@Greg.Bosworth]

@@BoomslangSuss yes thats true, but the portal boxes cause the tire centerline to sit below the lower links, which causes the portal box to want to drive "under" itself, which then pulls on the upper links from that leverage on the axle. may be a different topic, but is a large variable to consider when setting up geometry imo. ive tested myself that the resulting forces on the links arent in the same direction because of that, pretty easy to see with a "sloppy" setup

[@admercs]

Which chassis is this?

[@BoomslangSuss]

Poizd

[@joshuagregg7579]

Are those shock/spring settings just for this demonstration? Or do you actually crawl like that? Curious.

[@BoomslangSuss]

Yes, that is actually what I run. It just so happens to also be good for this demo because it's quite light oil which lets the shocks move more freely and isn't adding significant damping force. Heavier oil could be one more variable affecting the outcome. Also, the rear spring rate is not at full droop in an incline which you will see in my next video. Finally, having no front spring is approximately the same as a medium spring plus a hair band - they cancel each other out. Should be another video on that.

[@shaynejenkins446]

Now do it with an actual crawler instead of a robot.

[@BoomslangSuss]

Aren't they the same, just different levels of technology?

[@ClickClacksRcs]

Can’t wait to share in the lcg group maybe them guys stop trying to make them homebrew chassis that don’t work