Motor examples. Certain motors are very popular and we keep getting asked about them, this section gives our findings on a few of them. We are not the manufacturers and our opinions are just that and should not be relied upon as accurate specification. For accurate information please consult the motor manufacturer.
Bosch 750w motor
The Bosch motor is a good motor at a good price (available in small quantities from Bosch’s distributors). However Bosch make these in huge numbers and know accurately what they can do! The 750w rating is therefore accurate, rather than conservative! It applies strictly at full speed (maximum cooling) and the motor will still get pretty hot! 750w at 24v is 32 amps.
Because of this, do not expect the motor to be able to take a large overload percentage, or a long slow overload. In particular, if you stall the motor without a motor speed controller in circuit, the motor will probably burn out inside a few seconds. All 4QD motor speed controllers are protected and will limit the motor current to a level that is safe (for the controller).
The Bosch will take the output from controllers like the DNO-5, but should be used carefully with the DNO-10, Pro-120 / 150 or larger controllers – unless you only use the peak current for very short durations. The Pro-120 / 150 will supply quite enough current to get the Bosch uncomfortably hot, and if the stall is maintained for more than a few seconds, the motors will fry and smoke. Of course, for a robot, this may be what you want but for general use we can hardly advocate the use of a controller that has the capability of burning out motors!
Don’t ask us for how long the Pro-120 / 150 will deliver full current into a stalled motor before it (the controller) overheats. We have never tried it as we did not want to fry the Bosch! But into an Ohio motor it takes the best part of a minute to cause the Pro-120 / 150 to cut out. We do not think the Bosch would survive that long!
The Bosch motor is available in 3 versions. Two of these have Offset Brushes. These are therefore less efficient in reverse. It is also probable that, even on the reversible motor, there are slight offsets due to manufacturing tolerances. So, on a robot, where one motor is left side and the other right, one motor will always be in reverse. The effect is that you may get a steering bias in one direction going forward and in the opposite direction in reverse. If you adjust out the imbalance in one direction, you will increase the reverse imbalance! Very difficult to set up properly, unless you fit tacho generator feedback to both controllers.
So, check the matching of the motor speeds. If there is imbalance, either use tank style steering, when you can probably compensate manually. Or fit an additional lay shaft to reverse the rotation of one motor. Then both will be rotating clockwise in one direction and anticlockwise in the other direction.
The three Bosch 750w motors are:
- 0 130 302 001 for left hand rotation
- 0 130 302 013 for right hand rotation
- 0 130 302 014 which is bidirectional.
The first two have threaded shafts (one RH thread, one LH thread) and the difference is not just the direction of the screw thread on the motor shaft!
The moral is: beware when using motors with threaded shafts… these almost certainly will have offset brushes!
EMD are probably the world’s best seller of low voltage PM DC motors for small electric vehicles, though they have never made a significant impact on the US market. EMD make variations on all their motors so their motor numbers are ‘families’ rather than individual motors. They do three diameters of motors: PM44, PM 50 and PM63. PM stands, as you might expect, for Permanent Magnet. The 44, 50 and 63 are the armature diameters, in millimetres. The armatures are made in various lengths, so you get PM 44/25, /38 and /50. The PM50 comes in /25, /38, /50 and /70 whilst the PM63 comes in /50, and /100 mm armature lengths. Many of these sizes are uncommon!
EMD’s ratings are reasonably conservative and they will all stand a good short-term overload, so a 24v PM 50/63, rated at 250w (12a) may stand 50 amps for nearly a minute.
Probably their commonest motor, 12v versions are used on golf caddies whilst 24v versions are used on mobility aids (pavement scooters) and smaller golf buggies. Motor rating around 200w. PM63 is happy with 75-80 amps for short periods, mainly limited by the brushgear!
Also very common, used on larger golf buggies. (25v versions). Motor rating is commonly around 300-400 watts.
This is a 1HP motor with a C56 size frame. It is one of our favourite motors for test purposes. Although ‘rated’ at 41 amps, 24v, we regularly use it to test our controllers and several US customers use it with our 4QD-200 controllers. However it is an extremely conservatively rated motor. If Ohio’s other motors are equally conservatively rated then they are to be thoroughly recommended.
This motor was designed by Cedric Lynch who now works with Saietta Engineering.
The motor has been licensed to various companies so is available as Etek, Manta, Lynch Electric Motor and Agni.
It is available in various sizes/ratings. It is highly efficient and has a very low resistance compared with other motors, so it can sustain high currents for long times. It requires a controller that can sustain high continuous currents e.g. the 4QD-300.
This was once very popular but stocks are now low. It is name-plate rated at 29 amps – a continuous rating. However the motor has a d.c. resistance of 0.1 ohms, so stalled, you could expect the motor to draw up to 120 amps from a 12v battery. The motor, with gearbox but no mechanical loading, takes about 1/2 volt to overcome static friction. Off load it takes about 4 amps (with its own gearbox) so under actual working it will draw between 4 and 120 amps depending on the mechanical loading. For this reason we’ve found that the Porter 10XX is the most reliable controller for this motor. We have also tested the motor on 24v and it is quite happy (although the gear box is little noisy).
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