Official Baja SAE Forums Homepage
Forum Home Forum Home > General > Design Discussion
  New Posts New Posts RSS Feed - balance bar?
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

balance bar?

 Post Reply Post Reply
Author
Message
bajanoob View Drop Down
Double Secret Probation
Double Secret Probation


Joined: Dec/23/2016
Status: Offline
Points: 7
Post Options Post Options   Thanks (0) Thanks(0)   Quote bajanoob Quote  Post ReplyReply Direct Link To This Post Topic: balance bar?
    Posted: Dec/23/2016 at 4:47am
Hi everyone,

I'm in the process of finishing up a brake design, and I had a couple of things I wanted to ask about.  My team hasn't really used a balance bar before for brakes for our previous cars, and I'm wanting to implement one. However I'm finding that a lot of the parts that I would need  (clevis, ball bearing etc) are impossible to manufacture anyways, so I'm thinking maybe it would be better to purchase the balance bar? I've had limited experience with cars and BAJA in general, and there really hasn't been other people on the team that I could ask about this. What do other teams usually end up doing to get their brake balancing ? Do you guys purchase or build your own balance bars?

thanks in advance
Back to Top
RLM View Drop Down
Baja Godfather
Baja Godfather
Avatar

Joined: Nov/15/2012
Location: Hamilton, ON
Status: Offline
Points: 879
Post Options Post Options   Thanks (1) Thanks(1)   Quote RLM Quote  Post ReplyReply Direct Link To This Post Posted: Dec/23/2016 at 8:41am
We've built ours in the past. we put a spherical ball bush in the pedal and use spacers to space out the master cylinder connection. the connection to the master cylinders is accomplished with rodends so they can pivot freely.

Other than that, tilton offers one for sale, as does wilwood if i remember correctly. 
McMaster Baja Racing (09-Dec 2015)
Team Captain 2012-2015
Suspension Lead 2015-2016
Back to Top
Nate View Drop Down
Welding Master
Welding Master


Joined: Jun/16/2014
Location: Ames, IA
Status: Offline
Points: 268
Post Options Post Options   Thanks (1) Thanks(1)   Quote Nate Quote  Post ReplyReply Direct Link To This Post Posted: Dec/23/2016 at 11:13am
We've done it multiple ways in the past. The first was the way RLM said. The problem we had was too many degrees of freedom. it would balance properly, but the pistons going into the master cylinders would move radially sometimes.

Then we moved to a rigid system and adjusted "bias" by making one master engage before the other. This was difficult to bleed because once one piston was firm, you couldn't really actuate the soft one that still needed to be bled. As systems leaked, the bias changed.

Finally we moved to a purchased set from wilwood. Worked great, but cost the most. I liked wilwood's setup because the spherical ball bush in the pedal was free floating. The piston's clevis ends going on the balance bar were butted up along shims beside the pedal. That made the pistons move axially only. The bar took one nut to lock in place, and it kept the pistons straight no matter the bias. 
Iowa State University Cyclone Racing 2013 - 2016
Tech Director, DAQ, Media, Manufacturing, Radios
2016 - S&T, Maneuv, & Endurance Driver
"Because BAJA" "Because RACECAR"
Back to Top
bajanoob View Drop Down
Double Secret Probation
Double Secret Probation


Joined: Dec/23/2016
Status: Offline
Points: 7
Post Options Post Options   Thanks (0) Thanks(0)   Quote bajanoob Quote  Post ReplyReply Direct Link To This Post Posted: Dec/23/2016 at 9:37pm
thank you guys for your input!

one more quick question, my team was also wanting something that'll have the optimum balance over a range of deceleration levels, i.e. automatically re-adjust at different deceleration speeds. That's not achievable with a balance bar, is it? I mean like a self-adjusting bias bar? Because I always thought with a bias bar, you can only adjust it to provide optimized bias at one deceleration level, and to change that you would have to manually adjust it.

Back to Top
sujandinesh View Drop Down
Welding Master
Welding Master
Avatar

Joined: Dec/27/2013
Location: Eindhoven
Status: Offline
Points: 241
Post Options Post Options   Thanks (0) Thanks(0)   Quote sujandinesh Quote  Post ReplyReply Direct Link To This Post Posted: Dec/27/2016 at 8:59am
The balance bar in BAJA that are used are mechanical components which cannot automatically re-adjust themselves at different deceleration speeds. To do that, you would have to go a step ahead and couple that with control mechanisms and sensors that sense the deceleration required. 

However a BAJA car never attains such high speeds (hence decelerations) where biasing plays a major role. Why would you want to do that? 
RVCE BAJA: 2011-2015
General Motors: 2015-2016

Tire Testing - University Racing Eindhoven
Admin - BAJA SAEINDIA Forums
Back to Top
bajanoob View Drop Down
Double Secret Probation
Double Secret Probation


Joined: Dec/23/2016
Status: Offline
Points: 7
Post Options Post Options   Thanks (0) Thanks(0)   Quote bajanoob Quote  Post ReplyReply Direct Link To This Post Posted: Dec/28/2016 at 2:02am
we've had biasing issues in the past where our front wheels would lock up but the back wheels wouldn't, and this would be a problem during brake check at competitions.
Back to Top
sujandinesh View Drop Down
Welding Master
Welding Master
Avatar

Joined: Dec/27/2013
Location: Eindhoven
Status: Offline
Points: 241
Post Options Post Options   Thanks (0) Thanks(0)   Quote sujandinesh Quote  Post ReplyReply Direct Link To This Post Posted: Dec/28/2016 at 11:57am
I think that would be more of a rotor-caliper issue if you don't have an eccentric weight distribution. I have seen cars which manage to lock all wheels up more or less simultaneously without even using a balance bar. 

Considering the maximum speed and deceleration your BAJA car can achieve on an off road terrain, front wheel locking way too early than the back wheels is not a biasing issue. 
RVCE BAJA: 2011-2015
General Motors: 2015-2016

Tire Testing - University Racing Eindhoven
Admin - BAJA SAEINDIA Forums
Back to Top
RLM View Drop Down
Baja Godfather
Baja Godfather
Avatar

Joined: Nov/15/2012
Location: Hamilton, ON
Status: Offline
Points: 879
Post Options Post Options   Thanks (0) Thanks(0)   Quote RLM Quote  Post ReplyReply Direct Link To This Post Posted: Dec/28/2016 at 3:06pm
Originally posted by sujandinesh sujandinesh wrote:

Considering the maximum speed and deceleration your BAJA car can achieve on an off road terrain, front wheel locking way too early than the back wheels is not a biasing issue. 

Front wheels locking before rear IS a biasing issue. what needs to be remembered is that the amount of brake force front vs Rear is not only a simple issue of adjusting a bias bar. there are many more factors to be considered which adjust the brake force bias. working our way from the pedal to the wheels, we first have our connection from the pedal to the master cylinders. this is where a bias bar can be located or a perminant bias can be built in. this is where you determine how much of the pedal force will go to each master cylinder. next you have the pressure system, the ratio of the master cylinder size to caliper size and how many calipaers that master actuates, further develops the overall brake force bias. then you have the rotor and pads. if you are using different pad compounds front to rear and different rotor diameters, this will also effect your overall force bias. next you have your contact between the tire and the ground. running different tires front vs rear will give you different friction coefficients. the suspension system also plays a part as the weight transfer under braking also needs to be factored into the calculation to balance your overall braking forces.  the Bias bar is a great way to fine tune the brakes for the car based on the environment it is running in. HOWEVER, it is not a way of remedying a bad brake design. if your fronts are locking up quite a bit before the rears, look into adjusting the suspension to allow more weight to transfer to the front. this will mean the fronts need to work harder and the rears less hard. for future designs, look into smaller front rotors or larger rear rotors to balance out the braking forces (assuming calipers and master cylinders are the same front to rear). best bet is to create an excel sheet where you can input your component specs and output your brake torque per axle. then you want to balance these with slight bias to the front. you then want to make sure that these brake torques exceed the torque generated by a locked wheel. if you can put different components in each system (front vs rear) then play around with those as well. I know a lot of teams prefer to have common components though as that requires less spares and sometimes bulk buy discounts. 

Best of luck. 
McMaster Baja Racing (09-Dec 2015)
Team Captain 2012-2015
Suspension Lead 2015-2016
Back to Top
sujandinesh View Drop Down
Welding Master
Welding Master
Avatar

Joined: Dec/27/2013
Location: Eindhoven
Status: Offline
Points: 241
Post Options Post Options   Thanks (0) Thanks(0)   Quote sujandinesh Quote  Post ReplyReply Direct Link To This Post Posted: Dec/28/2016 at 3:37pm
Originally posted by RLM RLM wrote:

Originally posted by sujandinesh sujandinesh wrote:

Considering the maximum speed and deceleration your BAJA car can achieve on an off road terrain, front wheel locking way too early than the back wheels is not a biasing issue. 

Front wheels locking before rear IS a biasing issue. what needs to be remembered is that the amount of brake force front vs Rear is not only a simple issue of adjusting a bias bar. there are many more factors to be considered which adjust the brake force bias. working our way from the pedal to the wheels, we first have our connection from the pedal to the master cylinders. this is where a bias bar can be located or a perminant bias can be built in. this is where you determine how much of the pedal force will go to each master cylinder. next you have the pressure system, the ratio of the master cylinder size to caliper size and how many calipaers that master actuates, further develops the overall brake force bias. then you have the rotor and pads. if you are using different pad compounds front to rear and different rotor diameters, this will also effect your overall force bias. next you have your contact between the tire and the ground. running different tires front vs rear will give you different friction coefficients. the suspension system also plays a part as the weight transfer under braking also needs to be factored into the calculation to balance your overall braking forces.  the Bias bar is a great way to fine tune the brakes for the car based on the environment it is running in. HOWEVER, it is not a way of remedying a bad brake design. if your fronts are locking up quite a bit before the rears, look into adjusting the suspension to allow more weight to transfer to the front. this will mean the fronts need to work harder and the rears less hard. for future designs, look into smaller front rotors or larger rear rotors to balance out the braking forces (assuming calipers and master cylinders are the same front to rear). best bet is to create an excel sheet where you can input your component specs and output your brake torque per axle. then you want to balance these with slight bias to the front. you then want to make sure that these brake torques exceed the torque generated by a locked wheel. if you can put different components in each system (front vs rear) then play around with those as well. I know a lot of teams prefer to have common components though as that requires less spares and sometimes bulk buy discounts. 

Best of luck. 
Sure it is. 

But if it locks up way too early, then you have chosen the wrong caliper/MC piston ratios or rotor sizes and that is exactly what I meant which RLM has pointed out as well. 

Locking up way too early is not something that needs to be fine tuned but is a result of wrong parameter selection in your brake design and hence not a biasing issue. 

Requiring to sense the deceleration and controlling the bias based on deceleration is therefore not required if the problem is "one set of wheels locking up before the other".
RVCE BAJA: 2011-2015
General Motors: 2015-2016

Tire Testing - University Racing Eindhoven
Admin - BAJA SAEINDIA Forums
Back to Top
RLM View Drop Down
Baja Godfather
Baja Godfather
Avatar

Joined: Nov/15/2012
Location: Hamilton, ON
Status: Offline
Points: 879
Post Options Post Options   Thanks (0) Thanks(0)   Quote RLM Quote  Post ReplyReply Direct Link To This Post Posted: Jan/03/2017 at 10:43am
Originally posted by sujandinesh sujandinesh wrote:

Sure it is. 

But if it locks up way too early, then you have chosen the wrong caliper/MC piston ratios or rotor sizes and that is exactly what I meant which RLM has pointed out as well. 

Locking up way too early is not something that needs to be fine tuned but is a result of wrong parameter selection in your brake design and hence not a biasing issue. 

Requiring to sense the deceleration and controlling the bias based on deceleration is therefore not required if the problem is "one set of wheels locking up before the other".

Did you read any of what I just explained? The entire brake design is a Biasing equation meant to balance forces. in order to balance things, you need to bias. There are 2 main types of Bias; adjustable (read Bias Bar), and built in (read brake design). If your locking one axle before the other, that is a result of poor built in BIAS. This results form improper selection of rotor, master cylinder, and caliper sizes in order to balance the equation. Therefore, IT IS A BIASING ISSUE. Just not a bias bar issue. 

I do however agree with you on your last point that sensing deceleration and automatically adjusting bias accordingly is not necessary. 
McMaster Baja Racing (09-Dec 2015)
Team Captain 2012-2015
Suspension Lead 2015-2016
Back to Top
sujandinesh View Drop Down
Welding Master
Welding Master
Avatar

Joined: Dec/27/2013
Location: Eindhoven
Status: Offline
Points: 241
Post Options Post Options   Thanks (0) Thanks(0)   Quote sujandinesh Quote  Post ReplyReply Direct Link To This Post Posted: Jan/04/2017 at 7:44am
Well, I see the problem now. 

All along, when I said "Biasing issue", I meant to say "Bias/Balance bar issue".  
So when I said it was not a "Biasing issue" I meant to say that it wasn't a "Balance bar issue" but rather a poor brake design with respect to MCs, Calipers, rotors etc. 

Hope this clears all the confusion out! 
RVCE BAJA: 2011-2015
General Motors: 2015-2016

Tire Testing - University Racing Eindhoven
Admin - BAJA SAEINDIA Forums
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down



This page was generated in 0.063 seconds.