Limitless 2wd Speed runs?

[joshludden]

Parachute effect is fun though. Only for the first few rounds “end” of joke…

Did you land shiny side up in the end?

 

[K-BASH]

video an car is what made me to decide to try 2wd....apparently soft foams on rear are the way...he is running a 420gram tp3650-3080kv in car an with motor sitting behind rear axle is also a key to successful 2wd passes...weight distribution is key imo..I believe road temps are also key....with castle esc ya should be able to set up drag brake to slow car down without even touching brakes on the big end via % an speed of drag brake....I'll pursue 2wd next summer when road temps are higher..in thery 2wd should have much less resistance in drivetrain equaling less amp draw an more head room to gear up

 

[Jerold]

I think the bigger issue with a parachute that is intended as a fail safe will need a more complex setup than just a mechanism that releases the chute out the back. I've seen others try to do something like this and the deployment speed of a chute that just kind of falls out the back is sure to induce some seriously clenched sphincters as you wait and pray for it to catch the air to save your car from certain doom. I think dragging the parachute on the way back would be the least of your worries in such a scenario as you'd almost certainly be working the cramp out of your chocolate starfish. In such a case I think you'd be better off installing the handbrake module to lock up all four wheels and let the chips falls where they may.

But maybe you've already considered this and have a more elaborate rapid deployment mechanism in mind.

The parachute would not be the primary braking system. But it would help slow the car and put drag at the rear of the car, which means the front should be pointed forwards... or downwards if it's in the air. i.e. stabilize the braking.

To do it right I think it will take some experimentation. Not only the deployment mechanism, but the size of the chute(s). I've seen a few different ways to deploy it. Some people just release it and the wind drag pulls it out and opens up. Other's I've seen use a packed in a can with a spring to push it out of the can. I think the actual drag shoots use a spring loaded drag shoot. I would also need a servo that pulls the chute but I could probably make that also push the chute out.

Then I need to figure out how big it needs to be and what material to make it out of. Axle says use trash bags, but I don't know, he's the expert so maybe it's a good material?

In any case it would take some engineering and a lot of trial and error.

 

[Diem Turner]

The parachute would not be the primary braking system. But it would help slow the car and put drag at the rear of the car, which means the front should be pointed forwards... or downwards if it's in the air. i.e. stabilize the braking.

To do it right I think it will take some experimentation. Not only the deployment mechanism, but the size of the chute(s). I've seen a few different ways to deploy it. Some people just release it and the wind drag pulls it out and opens up. Other's I've seen use a packed in a can with a spring to push it out of the can. I think the actual drag shoots use a spring loaded drag shoot. I would also need a servo that pulls the chute but I could probably make that also push the chute out.

Then I need to figure out how big it needs to be and what material to make it out of. Axle says use trash bags, but I don't know, he's the expert so maybe it's a good material?

In any case it would take some engineering and a lot of trial and error.

Yeah, that's essentially everything that I was driving at. As for material, what about Mylar®? I have absolutely nothing to back this up with, but I feel like it would be a little more robust and would stand up to the repeated folding, packing, dragging along the road and repacking better. Dunno, just a gut feeling. I could be totally wrong.

 

[Cereal_killer]

video an car is what made me to decide to try 2wd....apparently soft foams on rear are the way...he is running a 420gram tp3650-3080kv in car an with motor sitting behind rear axle is also a key to successful 2wd passes...weight distribution is key imo..I believe road temps are also key....with castle esc ya should be able to set up drag brake to slow car down without even touching brakes on the big end via % an speed of drag brake....I'll pursue 2wd next summer when road temps are higher..in thery 2wd should have much less resistance in drivetrain equaling less amp draw an more head room to gear up

Interesting fact.

direct drive (1:1) gear, power is delivered directly through the main shaft of the transmission, so the only loss sources are windage, friction and drag, resulting in total at-the-wheel losses as low as 1.5 to 2 percent in a real car scenario… since I didn’t want to write nor screw up the point what I was trying to say I stole this from a website since it is pretty much worded the way I was intended at.

Did you land shiny side up in the end?

Of course. I never had good luck with it. No matter what I did to it it still wanted to flip over 70-75mph

 

[Jerold]

Yeah, that's essentially everything that I was driving at. As for material, what about Mylar®? I have absolutely nothing to back this up with, but I feel like it would be a little more robust and would stand up to the repeated folding, packing, dragging along the road and repacking better. Dunno, just a gut feeling. I could be totally wrong.

Mylar is an interesting choice. It's very light weight and super tough. You, assuming you're not the Hulk, can't tear it. But if you have a pin hole it tears easy through the flaw. But probably much better than a trash bag.

I did find this on Amain. It's for a rocket, but might be a good place to start.
https://www.amainhobbies.com/estes-pro-series-ii-nylon-parachute-24-est2261/p227491

It's a 15lb car going 100 whatever MPH, so maybe 2 of these, might help. Or they could just tear off on deployment.

 

[Tex Koder]

...

Where I run I have limited space, or at least it feels limited to me, and was thinking about a parachute to slow it down. It could also be a fail safe, if all goes wrong pull the rip cord. It would make driving it back a bit more complex because the chute would be dragging the car or dragging on the ground the entire time.


...

I think the bigger issue with a parachute that is intended as a fail safe will need a more complex setup than just a mechanism that releases the chute out the back. I've seen others try to do something like this and the deployment speed of a chute that just kind of falls out the back is sure to induce some seriously clenched sphincters as you wait and pray for it to catch the air to save your car from certain doom. I think dragging the parachute on the way back would be the least of your worries in such a scenario as you'd almost certainly be working the cramp out of your chocolate starfish. In such a case I think you'd be better off installing the handbrake module to lock up all four wheels and let the chips falls where they may.

But maybe you've already considered this and have a more elaborate rapid deployment mechanism in mind.

A parachute mechanism that can activate Quickly is not a problem.

I've been thinking about such a device for my SRX project (if I intend to make it a dedicated speed run rig, I will need more stopping power. Road space being limited around here.)
You can have it release the chute and then after your vehicle has slowed down enough ,have it cut-away the dragchute -that can be accomplished with just one servo.
How it works is in my head, I just need to CAD it out.

The parachute material is fairly simple too.
Use those heavy duty window screens that are designed to withstand pets from crashing thru.. They're tough stuff and because they are kind of firm flexy material they will expand out to shape quickly after ejection. Also because they are a type of mesh, it will be a bit more forgiving -braking wise- upon deployment than compared to a solid piece like a trash bag.. Those HD screens can definitely take multiple folds and abuse.

If you can retrieve them, it should be able to be re-used often (if it doesn't get blown away after separation.)

 

[Diem Turner]

Mylar is an interesting choice. It's very light weight and super tough. You, assuming you're not the Hulk, can't tear it. But if you have a pin hole it tears easy through the flaw. But probably much better than a trash bag.

I did find this on Amain. It's for a rocket, but might be a good place to start.
https://www.amainhobbies.com/estes-pro-series-ii-nylon-parachute-24-est2261/p227491

It's a 15lb car going 100 whatever MPH, so maybe 2 of these, might help. Or they could just tear off on deployment.

Yeah. Personally, I think I'd go with three or four of these instead. They look way cooler and you can get a comparable surface area for half to two thirds of the cost.
https://www.amainhobbies.com/estes-parachute-18-est2267/p802206

A parachute mechanism that can activate Quickly is not a problem.

I've been thinking about such a device for my SRX project (if I intend to make it a dedicated speed run rig, I will need more stopping power. Road space being limited around here.)
You can have it release the chute and then after your vehicle has slowed down enough ,have it cut-away the dragchute -that can be accomplished with just one servo.
How it works is in my head, I just need to CAD it out.

The parachute material is fairly simple too.
Use those heavy duty window screens that are designed to withstand pets from crashing thru.. They're tough stuff and because they are kind of firm flexy material they will expand out to shape quickly after ejection. Also because they are a type of mesh, it will be a bit more forgiving -braking wise- upon deployment than compared to a solid piece like a trash bag.. Those HD screens can definitely take multiple folds and abuse.

If you can retrieve them, it should be able to be re-used often (if it doesn't get blown away after separation.)

Oh I know that it can be done. There's nary a contraption I could conceive of that this forum doesn't have the know-how, skills and competence to draw up, design, print/mold/machine/fabricate, test, revise and improve in an iterative process as well or better than most other random conglomerations of like minded people across the internet.com.
I was just poking a little bit of tongue-in-cheek fun at the haphazard manner in which the idea of a fail safe parachute was thrown out there as it immediately conjured up images in my head of tense faces and postures awaiting the earth shattering kaboom as a sliver of mostly undeployed parachute flutters behind the car.

 

[Jerold]

Yeah. Personally, I think I'd go with three or four of these instead. They look way cooler and you can get a comparable surface area for half to two thirds of the cost.
https://www.amainhobbies.com/estes-parachute-18-est2267/p802206

True, but if memory serves me correctly (which is always a question), those are plastic. I suspect that they might tear out under the high load of a 1/7 scale car.

They are about the same cost/sq-in anyway, 7/100ths of a penny. If you factor in the cost of replacing the plastic chutes, the nylon will be cheaper.

But I think your right, we need more chute than just one or two. In this Traxxas video they jump a Slash off the roof and deploy a parachute (two) for the landing. I think they are using 2x 54" SKLZ parachutes.

• 54" X 54" chute provides approximately 15-30 lbs. of progressive resistance (depending on speed of user)

There are knock off chutes for about 1/2 the price.

I wonder how tightly we can pack them? Also it will add some weight to the car, the knock off says it ways 0.5 Kg (1.1 lbs).

 

[TN-RC]

I'm sure you could program it to function like that, assuming your Tx supports that sort of functionality. The only thing that would take some working out is: since the handbrake is a disc brake that gets clamped in a caliper, the amount of travel from barely engaged to fully locked isn't very far. So, if I'm understanding your intention correctly, I'd suspect that that a sort of Expo function would be necessary to slow the brake servo movement down as it reaches and goes beyond the point of engagement...if that makes sense.

What if the rod off of the servo had a spring on it like a Nitro throttle and the farther you push on the brake the harder the spring gets, that way you could not lock the front up and it would slip as much as it needs to.

 

[Diem Turner]

What if the rod off of the servo had a spring on it like a Nitro throttle and the farther you push on the brake the harder the spring gets, that way you could not lock the front up and it would slip as much as it needs to.

That's an interesting thought. I'd say it's definitely worth exploring to figure out what kind of spring load would result in a slow(er) progression of brake engagement. Good call.

 

[Hector_Fisher]

What if the rod off of the servo had a spring on it like a Nitro throttle and the farther you push on the brake the harder the spring gets, that way you could not lock the front up and it would slip as much as it needs to.

That's why I was thinking you might be able to find an old fireteam brake kit that most people take off and repurpose it. Tune the spring or channel setting to more slowly applies brakes.

 

[kspitters]

The spring idea sounds super smart @TN-RC
I’m very excited to see who brings this to life.

 

[TN-RC]

That's why I was thinking you might be able to find an old fireteam brake kit that most people take off and repurpose it. Tune the spring or channel setting to more slowly applies brakes.

View attachment 271453

Well, you got a start already I did not know it looked like this.

 

[TN-RC]

video an car is what made me to decide to try 2wd....apparently soft foams on rear are the way...he is running a 420gram tp3650-3080kv in car an with motor sitting behind rear axle is also a key to successful 2wd passes...weight distribution is key imo..I believe road temps are also key....with castle esc ya should be able to set up drag brake to slow car down without even touching brakes on the big end via % an speed of drag brake....I'll pursue 2wd next summer when road temps are higher..in thery 2wd should have much less resistance in drivetrain equaling less amp draw an more head room to gear up

If the weight is behind the rear axle it pulls up at the front and that is not something you want in a 2wd, you already have torque problems. I have been thinking about using a DR10M for a 2wd build, but I don't have the funds right now. With a 2wd car, you don't have power going to the steering wheels, so to turn, you are hoping that your plows on the front catch on the road.
The photo shows where on a 2wd car you want your weight. The other thing you can do is put a crazy amount of rake in the car, that is what mainly keeps my car on the road. After 70mph, I could hear the front tires trying to lift on my, 2wd build (the motor was behind the rear axle).

 

[dk10438]

When trying to brake with a rwd setup, is the primary issue the lack of braking power because most of the weight is on the front wheels or spinning out because of a severe oversteer condition due to weight being transferred to the front axles?

I’m building a serpent speed runner and the front axle is a one way which means in the forward direction the car is in 4wd but braking or reverse the front wheels spin freely which essentially makes it a 2wd….

 

[LibertyMKiii]

When trying to brake with a rwd setup, is the primary issue the lack of braking power because most of the weight is on the front wheels or spinning out because of a severe oversteer condition due to weight being transferred to the front axles?

I’m building a serpent speed runner and the front axle is a one way which means in the forward direction the car is in 4wd but braking or reverse the front wheels spin freely which essentially makes it a 2wd….

From my experience, it was the weight transfer causing a lack of grip on the rear tires. Usually, the rear tires would try to lock up and puts the car into a skid situation. You could probably setup drag back in the ESC to gently slow the car down for you.

I'd bet you can fully lock that front diff so it works for both accel and braking.

 

[dk10438]

got it. Spin outs are a result of locked up rear wheels and over steer. There isn’t some sort of abs?

The input cups go into the axle which have one way bearing. @phildogg told me who modifies his axles but I haven’t had any luck connecting with him. I was thinking I might try epoxy but that doesn’t seem strong enough.

There is some “drag assist” front axle that allow you to put in diff fluid but no one seems to have them.

 

[LibertyMKiii]

got it. Spin outs are a result of locked up rear wheels and over steer. There isn’t some sort of abs?

The input cups go into the axle which have one way bearing. @phildogg told me who modifies his axles but I haven’t had any luck connecting with him. I was thinking I might try epoxy but that doesn’t seem strong enough.

There is some “drag assist” front axle that allow you to put in diff fluid but no one seems to have them.

Some radios have ABS braking functions. They don't know or track the motor speed/position so I believe it is done via pulsing of the brake application. The only thing I clearly remember was that it should never be used with fast rc cars.
From memory, the issues are related to the heat build-up that the function creates or something like that....

 

[fozzy71]

video an car is what made me to decide to try 2wd....apparently soft foams on rear are the way...he is running a 420gram tp3650-3080kv in car an with motor sitting behind rear axle is also a key to successful 2wd passes...weight distribution is key imo..I believe road temps are also key....with castle esc ya should be able to set up drag brake to slow car down without even touching brakes on the big end via % an speed of drag brake....I'll pursue 2wd next summer when road temps are higher..in thery 2wd should have much less resistance in drivetrain equaling less amp draw an more head room to gear up

That is damn impressive with that SCT body. He could probably get the extra 1 mph to get his 140 if he just went with something aerodynamic from Delta.