RXV - Technical Understanding of Braking, Emergency vs Normal

[DB Cooper]

Brand new (to me) RXV, and I'm not a stranger to motor braking and regeneration as I have a Tesla. However, while researching this weekend on this site, I saw many people comment about emergency braking and how it can be tough on motor brakes, etc. Given mine is lifted with bigger tires and stock 235A controller, my regen is somewhat less than that of a stock cart, but it regens nicely. It does coast a little bit after initial throttle off then it starts to really slow down. I don't really have to use the brake pedal at all even with our hills. However, if I need to slow down more quickly, I can lightly press the brake pedal to initiate a pretty quick slow down. I've yet to use more than maybe 20% pedal travel.

I guess I'm trying to understand what if any friction components are being used. If you never press the brake pedal is there any clutch/friction? If you lightly depress it is there any, and if you slam on the brake most assuredly there would be. I can't find a real clear article on that.

Thanks

[Chevota Guy]

When you use the RXV brake pedal in typical fashion, there are zero frictional loads on the motor brake. The motor brake is either all off (typical when moving) or all on as when stopped or if one mashes the pedal to the floor as in a panic stop. That will lock the motor brake up, there is no gradual amount of friction, it's all or nothing.

In the pic below, you can see a switch on the left with a silver cylindrical plunger shaft. That is the electric motor brake emergency or panic stop switch. The pedal will be near full travel for that to trigger.

Since the RXV has a limited slip diff, both rear wheels will lock up near instantly.

[DB Cooper]

Originally Posted by Chevota Guy

When you use the RXV brake pedal in typical fashion, there are zero frictional loads on the motor brake. The motor brake is either all off (typical when moving) or all on as when stopped or if one mashes the pedal to the floor as in a panic stop. That will lock the motor brake up, there is no gradual amount of friction, it's all or nothing.

In the pic below, you can see a switch on the left with a silver cylindrical plunger shaft. That is the electric motor brake emergency or panic stop switch. The pedal will be near full travel for that to trigger.

Since the RXV has a limited slip diff, both rear wheels will lock up near instantly.

Thank you kindly for the great explanation, that alleviates my concern in using the brake more aggressively. If I read that right, effectively if the motor brake is activated, I'd lock up my rear tires/skid, that would be an indication, correct?

We do have deer on our streets, so just curious if someone panic stops, how robust are these things? I imagine golfers, drunk golfers, etc. panic stop frequently. Thus, are these designed for repeated panic stops or is it likely a single or short amount of panic stops would grenade the motor brake?

[Chevota Guy]

You are correct about the lock up and skidding if the motor brake is deployed while in motion. This is in sharp contrast to the regenerative motor braking that you feel from normal braking. The regen action can be quite strong depending on how far the pedal is pushed. This has led some folks to believe the electric motor brake is being used when it really isn't.

I don't have direct experience with the lock up at speed condition, but I have read several accounts here where folks have said that depending on speed the lock up can have a rather violent reaction such as lurching folks out of the seat into the steering wheel or windshield. Others have said that the emergency action will wear the brake prematurely, which would seem intuitive to me.

In the normal operation of the cart, the automatic electric motor brake function is used frequently when ever one stops for more than a couple of seconds or parks the cart. These conditions don't involve the cart in motion and is how the brake is supposed to be used.

[kernal]

I've posted this a couple of times and to date have not been challenged on it's accuracy:

This is how I understand the RXV braking system:

There are no wheel brakes. All normal braking is done by the motor using regen braking. Regen braking occurs whenever the gas pedal is up. The service brake pedal is present and when pressed, the controller increases regen braking to slow the cart faster. There is no mechanical linkage from the brake pedal to anything. It speaks to the controller electrically. The motor is capable of regen braking all the way to 0 rpm and can and does hold the cart stopped under any conditions (IE. on a hill) until parking brake engagement.

The parking brake, also referred to as the hill brake sometimes, is an electrically operated mechanical brake attached to the end of the motor. It’s operation is automatic requiring no input by the driver. It is fail safe to the engaged position and requires electrical signal to release it. When operating normally is is either all(100%) on or off. It is controlled by the controller as is everything else on an RXV.

The cart drives like an EV and is noticeably different than a standard DC motored golf cart. After some practice you can do a lot of single pedal driving. The service brake pedal feels like power brakes on an automobile to me and is very effective at slowing the cart beyond normal regen. Usually I just have to tap it a time or two. If you have a digital meter on the cart you can see the voltage of the battery pack increase during pedal up “coasting” and a dramatic and rapid increase if the service brake is pressed. I have seen over 60v momentarily when using the brake. When bringing the cart to a stop, the motor holds the cart for a second or two and then the parking brake engages. You can hear it. There are NO detrimental effects to using the SERVICE brake under normal conditions.

Exception: The parking brake will engage while the cart is moving if you mash the service brake far enough, like in a panic/emergency stop. I think Bob Boyce has posted that this is about 60% of brake pedal travel. In my experience you won’t do this accidentally under normal operation. I have had to do this twice in 2 years (panic stop). The rear wheels (both) lock immediately. It was not a violent experience and I was at speed. I don’t know how many times you can do this before damage to the brake occurs but it is not designed to do this a lot.

2 more years have gone by since I first posted this. I have not had any issues with the E brake as EZGO calls it. Electric RXVs have a limited slip diff. There may be multiple reasons for this but one is if the diff was open like other carts there would be no braking at all, regen or otherwise.

I haven't come across any data as to how many times you can engage the Ebrake with the cart in motion but it certainly is a limited number.

The brake can also fail or partially engage due to corrosion or some other phenomenon that isn't clear to me. I know this is happening because it is reported here occasionally. Ebrake failure is usually associated with pungent smell and/or failure to release during POST when ignition is switched on. It is not difficult to replace yourself but check this board for instructions if it ever comes up.

The RXV is computer controlled and sensitive to voltage (low). Important to keep batteries charged and avoid/control corrosion.

edit: chevota guy has made some important comments and I agree with him

[DB Cooper]

Originally Posted by kernal

I've posted this a couple of times and to date have not been challenged on it's accuracy:

This is how I understand the RXV braking system:

There are no wheel brakes. All normal braking is done by the motor using regen braking. Regen braking occurs whenever the gas pedal is up. The service brake pedal is present and when pressed, the controller increases regen braking to slow the cart faster. There is no mechanical linkage from the brake pedal to anything. It speaks to the controller electrically. The motor is capable of regen braking all the way to 0 rpm and can and does hold the cart stopped under any conditions (IE. on a hill) until parking brake engagement.

The parking brake, also referred to as the hill brake sometimes, is an electrically operated mechanical brake attached to the end of the motor. It’s operation is automatic requiring no input by the driver. It is fail safe to the engaged position and requires electrical signal to release it. When operating normally is is either all(100%) on or off. It is controlled by the controller as is everything else on an RXV.

The cart drives like an EV and is noticeably different than a standard DC motored golf cart. After some practice you can do a lot of single pedal driving. The service brake pedal feels like power brakes on an automobile to me and is very effective at slowing the cart beyond normal regen. Usually I just have to tap it a time or two. If you have a digital meter on the cart you can see the voltage of the battery pack increase during pedal up “coasting” and a dramatic and rapid increase if the service brake is pressed. I have seen over 60v momentarily when using the brake. When bringing the cart to a stop, the motor holds the cart for a second or two and then the parking brake engages. You can hear it. There are NO detrimental effects to using the SERVICE brake under normal conditions.

Exception: The parking brake will engage while the cart is moving if you mash the service brake far enough, like in a panic/emergency stop. I think Bob Boyce has posted that this is about 60% of brake pedal travel. In my experience you won’t do this accidentally under normal operation. I have had to do this twice in 2 years (panic stop). The rear wheels (both) lock immediately. It was not a violent experience and I was at speed. I don’t know how many times you can do this before damage to the brake occurs but it is not designed to do this a lot.

2 more years have gone by since I first posted this. I have not had any issues with the E brake as EZGO calls it. Electric RXVs have a limited slip diff. There may be multiple reasons for this but one is if the diff was open like other carts there would be no braking at all, regen or otherwise.

I haven't come across any data as to how many times you can engage the Ebrake with the cart in motion but it certainly is a limited number.

The brake can also fail or partially engage due to corrosion or some other phenomenon that isn't clear to me. I know this is happening because it is reported here occasionally. Ebrake failure is usually associated with pungent smell and/or failure to release during POST when ignition is switched on. It is not difficult to replace yourself but check this board for instructions if it ever comes up.

The RXV is computer controlled and sensitive to voltage (low). Important to keep batteries charged and avoid/control corrosion.

edit: chevota guy has made some important comments and I agree with him

Thanks so much, very helpful. I probably got to 40-50% braking force today, cart slowed down very fast!

[cgtech]

Chevota & kernel are both on it, close enough to perfect I cant say much to revise it. You will likely soon Love the "just tap the brake pedal, and not much more is needed" driving style, it just does most of the rest automatically. I never put the rxv brake pedal past about 20%, unless someone is slamming on the brakes in front of me. It's usually "just a light tap", and it knows I wanted to slow down & does the rest, until I get "just behind" the stoping point, one more tap and it's totally stopped. Even if you are intentionally "flying around the neighborhood", not much brake pressure is needed to get stopped at the red sign once you get a feel for how it works (and how its different from any cart you've ever used before).

Some people cant get used to it, especially ones who had "not so good brakes" on the car they"traded-in", they "mash it to the floor". I do understand the "brake pedal feel" thing, because RXV brake pedal doesnt have the "you've about hit the max of your brakes" feel of conventional brakes, but, instead a pedal that just gets "more spring resistance" the harder you push.

But, if you let your kids drive it, they will be locking that motor brake up all the time, smashing the pedal since they dont understand, which will eventually cost $. Shouldn't be a problem at all for DB Cooper.

[DB Cooper]

Originally Posted by cgtech

Chevota & kernel are both on it, close enough to perfect I cant say much to revise it. You will likely soon Love the "just tap the brake pedal, and not much more is needed" driving style, it just does most of the rest automatically. I never put the rxv brake pedal past about 20%, unless someone is slamming on the brakes in front of me. It's usually "just a light tap", and it knows I wanted to slow down & does the rest, until I get "just behind" the stoping point, one more tap and it's totally stopped. Even if you are intentionally "flying around the neighborhood", not much brake pressure is needed to get stopped at the red sign once you get a feel for how it works (and how its different from any cart you've ever used before).

Some people cant get used to it, especially ones who had "not so good brakes" on the car they"traded-in", they "mash it to the floor". I do understand the "brake pedal feel" thing, because RXV brake pedal doesnt have the "you've about hit the max of your brakes" feel of conventional brakes, but, instead a pedal that just gets "more spring resistance" the harder you push.

But, if you let your kids drive it, they will be locking that motor brake up all the time, smashing the pedal since they dont understand, which will eventually cost $. Shouldn't be a problem at all for DB Cooper.

Yup, I agree entirely, for any normal slowing down, no more than 20% is needed to sort of kick start it. I'd say the one downside of the RXV, particulary in my configuration (more later) is that it isn't really a cart you want to just throw the keys to your friend who's had a couple drinks and just go drive around. The double click brake unlock, the brakes in general, etc. take some understanding. Given we got the prom queen package on our cart with a super fresh paint job, I won't be handing this out to kids or young adults or even adults unless they've been trained.

As stated, and I'm aware of the issues, but mine are exacerbated by 23" wheels and a non-customized controller (Just Freedom+Mode4). The lower speed engagement is a bit delayed, and I could see people wanting to apply too much throttle then the cart just takes off. I also have a 6" lift whereas I'd want a 3" lift but the builder who normally uses 3" was having such a hard time getting anything in stock and was able to get some 6" lifts. I'll be looking to swap out for a 3" later and downsize the times a bit. 23" + 6" + Corners isn't the most confidence inspiring affair, but it is pretty stable at speed. If I can get the 23" to work with the 3" (which the builder says will work with shaving the rear bumper/fender which he already did), I might stick with that and go 350A and see if I can track Bob down (or you) or hope someone makes it to Austin. Surprisingly, with some reasonably steep hills (I live in an area of Austin called "Cat Mountain"), I have no torque issues going up hills.

Anyways, thanks for the detailed explanations, at first I couldn't quite figure out if there was a friction component and when it activated and was quite gun shy about using the brake altogether.

[AlexBen]

What a phenomenal explanation.

I’m admittedly new to my cart, and was unhappy about the current “locked E brake” as mine came to me in need of help. Dead batteries and corroded wires.

I’m pretty handy, so I was initially looking for ways to just delete the E-Brake.

It seems worth retaining after all. But I’ll wire up a bypass switch to supply just enough juice off a Dewalt 18v pack to unlock brake on case I need to push a dead cart.

[Volt_Ampere]

You absolutely do NOT want to delete the E-Brake! It is a very important safety feature. If the cart loses power, you would have zero braking ability without it. It is very reliable if you don't abuse it. It should not engage when you are moving unless you MASH the brake pedal. It engages when you come to a stop to hold the cart without using battery power. That puts very little wear and tear on it. If you have a Lithium battery that can shut off completely, then you might want a way to release the brake like you mentioned. It only takes about 12V to activate the brake and it doesn't take a huge amount of current. With FLA batteries, the brake should still release in TOW mode even if the batteries are very discharged. But I have seen two cases where two of my buddies had the Lithium BMS trip on low battery. Wheels locked up and the cart could not be moved without either resetting the BMS or removing the brake from the motor. One guy was close enough to a house to run an extension cord to plug in his onboard charger. That revived the battery and we could push the cart out of the way while it got enough of a charge to drive home. The other guy was in the middle of the street - not good. He got someone to remove the brake for him so they could tow the cart to his house. Both cases were "user error" letting the battery get too far discharged. Lesson learned for them. I don't have an RXV but if I did, I would have a method to release the brake in case of a BMS shutdown. I have a bunch of 3S lithium batteries for model flying. I could use one of those to activate the brake for towing. I would rig a connector to do that.