Golf Cart/Bicycle Hybrid

[kuntrywelder]

Hey guys, I have a picture of this rig in my album. It is a 4 wheel bicycle I had that was great but couldn't handle the hills around here. I found an old Cushman Golfster with a good motor and "married" the swingarm and differential/motor assembly to the bike while carefully keeping the balance. I tossed the power wasting resistor throttle assembly in favor of a conversion to a twist grip throttle and controller. Because I had lightened it so much I went the cheap route on the controller (all I could afford) and used a Golframa Curtis 1204 275 amp controller thinking it would be enough. It has enough acceleration and speed on flat ground for pickups and deliveries which is its intended use but it feels like the controller is almost shutting down on hills and especially if I can't get a run, like my driveway. I wanted to bypass the controller on hills and found a diagram of how to do it submitted by Roady 89. I don't think I need a voltage boost, just a bypass. I have some questions from you electrical guys. Will I get a significant improvement from a bypass without a voltage boost? Do I need a diode on A2 terminal or just on M-? What size diode(s) and where is the best place to get them? Thanks.

[dougmcp]

It could be the combination of controller, cables and motor that is your issue, series motors slow on hills and you need amperage to overcome it.
A bypass will do no real good and a boost is troublesome.
There should be a solution.
Can you post the picture and specs of your unit here?

[kuntrywelder]

Hello, I haven't figured out how to post photos in a post, there is a photo of the rig in my album. The motor is the stock unit that came with the old Cushman Golfster. It is a General Electric 36V and it looks like it says 55 Amps. The cables are the same gage welding cable I use in my shop on my small shop welder. The controller is a Golframa refurb. of a Curtis 1204- 275 Amp. no high pedal disable. The controller had just been refurbed when I bought it. I made the rig weigh less than half of what the Golfster weighed and I expected it to handle these hills around here a lot better than it does. The batteries are 3 Optima yellow top deep cycle rated 750 CCA wired in series. They are in excellent shape so I don't think that is the problem. Maybe I expect too much but with 2 people on it it will shut down and quit going up my very steep driveway unless I get a real good run at it. I thought maybe the controller just limited out when in a bind so a bypass would prevent the controller from limiting the amperage the motor could get. Thanks.

[sonicj]

sounds like you need to gear it down or rewind the motor with more turns. either way, you'll lose top speed but will gain torque. cool project!
-sj

heres your pic for ya:

[dougmcp]

Unless the controller is truly shutting down or going into thermal overload, that may not be your problem.
The optima yellow tops are a deep cycle battery but have around 1/3 of the reserve power of a true deep cycle lead acid battery and they may be part of your problem with the torque issue. Maybe you're not getting a full charge on these, after a charge and rest they should be in the 12.7v range (38.2v total).
I would clip your meter to the 36v pack and take the cart for a ride when you hit the steep driveway see how low the voltage goes when you're asking for the torque. I would say anything less than 32.5v (a 15% drop [38.2v x 0.85]) and you have a battery problem.
If the voltage holds then look at the connections and/or cables.
You can also put a meter on the controller and see if it is limiting your voltage to the motor.

[kuntrywelder]

Thanks to the guy that posted the pic for me. Guess I'm "computer challenged" as well as electrically challenged. I enjoy building these projects but usually stay with gas engines. The batteries will stay above 39V for days after a full charge. I put the rig against my truck and twisted the throttle and it stayed above 34V. I will try to meter the voltage from the controller in the same way when I get a chance. I don't have any way to check how much amperage is going through the controller but it never even gets very warm even after a trip to town (15 miles round trip with a rest while I eat lunch there) and the pack will still be above 35V when I get home. The motor will be a little bit hot but not in the danger zone. Thanks for the help guys.

[dougmcp]

Sounds like the battery bank is fine and if the controller is stying really cool, I doubt that is an issue.
Just guessing here but some of the really old Cushman's had a 1 HP 24v motor which was also rated at 1.5 HP at 36v and maybe the motor just doesn't have the guts to do what you want.
Do you have a Forward/Reverse? Are all the cables associated with power the same gauge?
Maybe a motor teardown and new brushes and a good cleanup might do it.

[kuntrywelder]

The motor tag is all but unreadable, it set for a long time at an old golf course shoved back into the bushes. I didn't wire up the old F/R switch because the rig is so light you just pick up the front end and spin it around. The cables are all welding cable. The only thing I can read on the label very well is 36V with no other listing. Maybe I just expect too much from this old motor. I did locate some aftermarket brushes but haven't put them in because I read somewhere you should run the OEM brushes as long as possible because the aftermarket ones were not as good. Maybe I should just look around for another motor. Thanks.

[sonicj]

i can't think of a reason to hang on to the old brushes. if you have a lathe you can turn down the commutator to make it smooth again. if not, your local motor rebuilder or machine shop can likely turn down the comm for a few $$.

this is a example of a worn commutator. the upper area is what the comm should look like. the lower portion is obviously worn. torque is a function of current; fresh brushes on a freshly turned comm will make better contact and allow for more current to pass through the motor. ie: more torque. another thing to look for is to make sure the brushes are fully seated on the commutator. if the armature isn't pushed deep enough into the motor can, the brushes won't make full contact with the comm (since they are hanging off the end) and you will lose torque. ymmv.

i would like to see how you coupled the motor to the transmission/freewheel/cassette/whatever. is shifting gears out of the question?
-sj

[kuntrywelder]

Thanks for info. I have a lathe but am not sure about taking the motor apart and working on it, I am much more comfortable in a machine shop. Actually, the motor is still coupled up to the differential just the way Cushman left it. I just removed the whole bicycle drivetrain and welded the golf cart "swingarm", motor, differential, disc brake and all in its place. I left the pedals for footrests and left the chain on to confuse the local constabulary. Someone suggested it might be a 1 1/2HP motor but it says 53 Amps on the tag so I think it is the later 3 HP motor. They also suggested I check the voltage coming out of the controller and I did that today. I put the rig against my truck and twisted the throttle full on and measured the voltage from the positive terminal to M- and it said between 5 and 6 volts. I then checked it with the rig jacked up and no load and full throttle voltage was 37 volts., I think the controller is shutting down under a load. It hasn't been run 20 hours since it was refurbed. I might have gotten a lemon-wish there was a good shop around here to check it for me. Fabrication, welding, and machine work is my experience. Thanks.