Mini Quad Project

sonnydlit · 11-06-2008, 03:39 AM

Hello and thanks for letting me join. I had previously bought my 6 year old a Doodle Bug but he then told me he wanted a quad. I decided to use what I could from the Doodle Bug and build him one. I purchased the Grasshopper plans online and scaled them down about 20% since he is a little guy. I also had to modify as needed due to the reduction in size and the fact that I wanted to use the engine mount portion of the Doodle Bug frame. I also used the stock Doodle bug Brakes and controls on it. Since he is light the stock Doodle Bug motor is fine for now. I simply added a jack shaft to gear it down and lightened the clutch shoes for a better take off. It is still a slug but it does not scare him so it is doing the job. I used some Go Kart wheels I had for the front (not matching for now though) and the stock Doodle Bug tires for the rear. I got some shocks from a ATV/buggy store here in Albuquerque and modified the mounting points from the mounting points in the plans for better leverage on the shocks so the suspension is compliant even with his 50 lbs on it. If I sit on it it will just about bottom out. It has also increased the suspension travel plenty. The small quads out there all have way too stiff of suspension for the riders that are actually small enough to ride them. This thing has ridden like a Cadillac for the few test rides he has taken it on. Since there is so much travel I had to make a chain tensioner linked to the frame that takes up the chain slack as the swing arm moves upwards. The front also developed lots of bump steer so I had to seriously modify the mounting points of the tie rods on the steering spindles to take away some of the bump steer. Now all I have to do is Weld the seat mounting straps to the frame to get rid of the bungee, make a few little mods and oh yeah, take it all apart and paint it. After I mounts some fenders to the thing first that is. I know it looks like Frankenstein but it makes him happy so it is serving it's purpose.

Sonnydlit

**jimh** · 11-06-2008, 12:04 PM

Nice job so far. Looking good. Good to see more people using their talents and creativity. Paint her up and post more pics. Should look good.

jeep2003 · 11-08-2008, 06:29 PM

cool . Id bet your bump steer is because of the angle of the spindles. The tops should be actually tilted inwards a hair and tilted back. take a look under a 4wd truck. the tie rod position is also important but not as much.

alfalfa · 11-08-2008, 07:15 PM

looks like a chopped up doodle bug? nice work!!!

**vinny b** · 11-09-2008, 04:05 PM

I built that damn Grasshopper too. I had nothing but problems with the steering on that thing. That thing would go straight no matter how I turned that steering wheel. I even had them go over the whole project via pictures and they said it looked perfect. I eneded making it a three wheeler, then a two wheeler, then a reverse trike and then finally back to a four wheeler. Then......I cut it up in pieces and never missed it. Sounds like you are having good luck with yours. Have fun with it.

It did go like a bandit though with the 6 HP and torq-a-verter...

sonnydlit · 11-09-2008, 10:44 PM

Hello and thanks for the comments everyone. The front spindles/axles do not come straight off of the pivot. In other words, while the bolt does go straight down thru the pivot point, the axle is welded to it at an upward angle. If the suspension arms where level the wheels would have some camber. They are also tilted back slightly as suggested. The quad actually turn pretty good with the intended rider. If I myself get on it it will not turn but I way 250lbs and it is way to small for me and practically wheelying from my weight so I did expect that. Your right Alfalfa, the engine mount section of the frame was cut from a Doodle Bug. Good catch. I believe my Mini Grasshopper turns decent due to the fact that I differed from the plans in a few areas which are apparent from looking at the pics of the 2 grasshoppers above. I have mounted the motor as far forward as possible which loads the front wheels for better traction. Also, if you look at the mounting points of the rear axle, mine mounts at the rear of the seat. The plans show it mounted further forward. The axle being mounted at the rear of the seat also helps to transition weight to the front wheels and causes them to have more bite and therefore helps the quad to steer better. Also, since the axle in the plans is mounted further forward and basically in the middle of the seat, if a passenger is on board or if a rider likes to sit to the rear of the seat it will causes a seesaw effect using the axle as the pivot point. This will causes the front wheels to seriously unload and skid straight. It probably does great wheelies though. LOL.

jeep2003 · 11-09-2008, 11:03 PM

the spindles should be tilted like the green rather than the red and back slightly. It might be just the picture but it looks off.

sonnydlit · 11-10-2008, 12:03 AM

Hello and thanks for the pic. Should that have negative camber at ride height or at when the suspension arm is parallel to the ground? They do have negative camber when the suspension arm is parallel to the ground. I maybe should have built the arms with negative camber at ride height instead but I was unsure how much negative camber it would have when the suspension was near full compression. I did build some positve caster into the front end so they are leaned back some. I think I am going to build another set of arms with adjustable camber as the attached pic shows. What do you think? Thanks again.

Sonnydlit

jeep2003 · 11-10-2008, 10:27 AM

When the rider is on it. I would build it so the axles are parallell with the ground and the spindles with very slight negative camber off the axle. And the arms paralell with the ground as well as the tie rods. I think its the positive camber thats trowing things off. I built my gocart with the spindles 90 degrees to the axle and very slight caster and it rides good. I like your idea making it adjustble

sonnydlit · 11-10-2008, 01:23 PM

Hello Jeep2003. Again, thanks for the input. I was wondering if your go-kart had single arms like the quad or double (upper and lower) arms. Also, how much wheel travel does it have so i can get an idea. I changed the shock mounting points and such on the quad so the wheel travel was increased.

Thanks again,
Sonnydlit