Racing Power Wheels Part 10: New Hydraulic Brake System

So the first braking system on the Power Wheels Dune Racer wasn't working really well in stopping the car. So we ordered a new hydraulic braking system that was shown in the last blog post. I got around to installing it on the Power Wheels with some parts of the previous braking system and with the help of Bryan from here. Below is a picture of the original braking system with the metal linkage.

The first thing I removed was the linkage that was being held to the frame with the use of brackets and bolts. I also removed it from the brake lever of the caliper. Below is a picture of the linkage removed from the Power Wheels.

The next thing to do was to remove the caliper and the bracket for the caliper. You can see what I am referring to in the picture below.

I then went ahead and removed the wheel to have access to the brake caliper. This caliper is a floating caliper that floats on the brake disc and glides on the bracket. So by removing the disc I am also removing the caliper. Below is a picture of the caliper removed with the bracket left in place. 

I then removed the brake disc and the brackets. Below is a picture of the components of the old braking system. From left to right, the parts are the linkage, brake disc, caliper, and the mounting brackets.

The new braking system that will be incorporated will be a hydraulic brake kit from BMIKarts.com. Below is a picture of the kit and the link to the kit is http://www.bmikarts.com/1-or-1-14-Cast-Aluminum-Hydraulic-Brake-Kit-_p_583.html. You get the option of choosing a 1" or 1-1/4" bore and between a 1/8" or 3/16" thick brake disc. We went with 1" bore because of the axle and a 3/16" brake disc

In the picture above you can see brake hoses, brake disc hub, master cylinder, brake disc, and the two-piece caliper. You could also see the DOT 5 brake fluid towards the top of the picture. It's purple and inside a cylindrical container. So the first thing I did was to bolt the brake hub to the brake disc. Then I slid the brake disc onto the rear axle as shown below. I later on reinstalled the brake disc so the slots would be orientated the other way, which can be seen in pictures ahead of the one below. 

I then had to come up with a way of attaching the caliper to the frame in hold it in place. So I was playing around mocking up the setup to try to imagine how to attach the caliper to the frame. Below is a picture of only one piece of the caliper with a bolt holding it to the frame. I drilled the hole after some playing around of the placement of the caliper. I approximated the placement of the hole into the frame and got an OK placement. An additional thing I want to comment on is the orientation of the calipers. From researching online, it is desirable to have the bleeder valves on top of the hose connectors. In the pictures below, the bleeder valve is what has the black rubber coverings. The bleeders need to be on top of the hose to allow air to be released from the braking system when it comes to bleeding the system.

So the next thing to consider was on how was I going to hold the bottom part of the caliper in place. There was no piece of frame that hang that low to be able to run a bolt straight through into it so I had to improvise. I had to find a way to bolt the caliper in place and to the frame. So I was thinking of some kind of flat piece of metal to do the job. But that may cause the brake caliper to rotate around the one single bolt that goes into the frame over time. So I was thinking maybe a L-shaped bracket to prevent it from wanting to rotate it. So I had to look around for some scrap metal or something to make it work.

Luckily, I still had the remaining parts of the first brake kit. So I decided to use the old caliper bracket from the first kit. So the first thing I did was to place the bracket on the frame and marked where the top bolt would need to go through. It wasn't exactly lined up with the pre-drilled holes of the bracket. Below are some pictures of the bracket and the newly drilled hole.

Once I was finished drilling the hole I then went back to test fit it on the frame with the caliper. Below is a picture of one piece of the caliper with the bracket on the frame.

In the picture above, the bolt wasn't long enough to go all the way through the caliper, bracket, and frame tubing. So eventually I had to go to Home Depot to buy longer bolts than the ones provided in the hydraulic brake kit. I was happy with the approximate location of the caliper. So the next thing to do was to drill the bottom hole in the bracket. I marked where the hole is to be and drilled a pilot hole as shown below.

I then proceeded to drill the hole all the way to its desired diameter as shown below.

I then went ahead and tested the alignment of the holes of the bracket with the holes of the brake caliper. Everything checked out good. Below is a picture of the bracket with one caliper piece being bolted to the bracket.

Below are pictures of the parts being used so far such as the mounting bracket, bolts, and the brake calipers.

I then went ahead and mounted the complete caliper with the bracket onto the frame. Below is a top view of the caliper installed.

The next thing to do was to now install the master cylinder somewhere on the frame. We still wanted to do a handbrake type of thing so we decided to install the master cylinder somewhere on the left side for the driver to pull while the right hand is being used for the throttle. I went to the frame and marked the outline of where the master cylinder will be placed as shown below.

I then used a marker to mark where the holes of the master cylinder are at. I then drilled those two holes into the frame and then installed it onto the frame. I didn't pictures of the drilled holes but below is a picture of the master cylinder installed onto the frame.

The next thing to do was now to install the brake lines/hoses to connect the master cylinder to the brake calipers. I forgot to take pictures of this process but it was pretty straightforward. You would unscrew the caps to reveal some kind of metal piece underneath the caps. I then fed the brake lines through those caps and into that metal piece that was held in place underneath the cap. I then bolted the caps on the threads as the instructions shown on the website of the brake company that manufacture this brake kit. The link to the instructions is http://www.mcpbrake.com/bleeding.htm. I marked the caps to count the number of turns I performed as shown below.

The instructions state to perform two full turns from finger tight. The next process to do was to fill up the master cylinder and to bleed the brake system. I performed this job with the help of Bryan. We somewhat followed the instructions from MCP Brakes. We first filled the master cylinder, Then I would pull back on the brake lever to pump the fluid through the system and hold that lever in place while Bryan would unscrew the bleeder valve to release air. Then he retightens the bleeder valve. After he tightens the bleeder valve, I release the lever. We periodically fill the master cylinder to prevent air from entering the brake lines. We performed this procedure until we got a good firm feel to the brake lever and see that the calipers clamp onto the brake disc. Below is a picture of the final work done.

Once that was done we decided to give the new brake system a test. To make pulling back on the lever easier we used a piece of PVC piping to provide more leverage on the brake lever. The setup so far with the body of the car back on can be seen below.

We did some laps around the building and the brakes worked much better than the mechanical disc brake kit. The hydraulic brakes stopped the car immediately with anyone driving it. It was a major improvement and made the Power Wheels much safer to drive. But, we still have the unstable steering at higher speeds that I will work on next. Later I put on zip ties to hold the brake lines in place, as shown below.

I wanted a better looking brake lever so I modeled a couple simple levers in SolidWorks and 3D printed the most simple one as shown below. 

Before printing a handle, I did a simple stress/displacement analysis of one of my initial design as shown below.

For the model above, I applied ABS as the material of the handle since PLA was not an option on SolidWorks. I applied a load of 10 pounds that was concentrated mostly at the top to create a worst case scenario kind of thing and fixed the 3 holes as fixed points. I ran the simulation and came up with the results above. According to the results, the maximum displacement occurred towards the top with a 0.08mm displacement which is very small. On a stress plot, the maximum stress of .4237 psi occurred towards the top of the top hole. So this gave promising results but 3D printing a handle doesn't give me a fully solid part like the once in SolidWorks. So the actual results may differ.

I was also worried if the PLA might not hold up to the torque required to turn the brake lever back but I was surprised that it did it without a problem. ABS is less brittle than PLA but we went with PLA since we have lots of PLA in stock. Below is a picture of the 3D printed handle on the brake lever.

The holes of the handle didn't line up perfectly with the holes of the brake lever. The holes of the handle were created in the center of the handle while the holes of the brake lever were more closer to one edge then another. But the handle had a pretty snug fit over the brake lever and stayed in place. The handle worked well in testing.

When designing the handle, I kind of wanted a contour shape that can conform to a hand. But my efforts weren;t perfect. I will work on making another handle. But in the meantime, this handle does the job. The next post will be on fixing the caster of the front wheels to make the steering more stable. Thanks for reading!

July 14, 2016